|
Home > Archive > Electrical Engineering > June 2006 > 10 metres audio cable going into PC = too long?
You are viewing an archived Text-only version of the thread.
To view this thread in it's original format and/or if you want to reply to
this thread please [click here]
| Author |
10 metres audio cable going into PC = too long?
|
|
|
| I am in the UK.
I would like to take a stereo signal from the line-out of my stereo
(or TV) to the line-in of my PC.
The equipment is in different rooms and the audio cable would be 10
metres. It will be this type:
http://www.maplin.co.uk/images/full/130i0.jpg
I don't understand the technical side but is 10 metres so long that
it might cause audio problems with things like frequency response or
voltage/current levels and so on?
Will I need to get some higher specification audio cable to cover
that distance? I want to keep cost down.
| |
| Palindr☻me 2006-04-18, 7:21 pm |
| Andy wrote:
> I am in the UK.
>
> I would like to take a stereo signal from the line-out of my stereo
> (or TV) to the line-in of my PC.
>
> The equipment is in different rooms and the audio cable would be 10
> metres. It will be this type:
> http://www.maplin.co.uk/images/full/130i0.jpg
>
> I don't understand the technical side but is 10 metres so long that
> it might cause audio problems with things like frequency response or
> voltage/current levels and so on?
>
> Will I need to get some higher specification audio cable to cover
> that distance? I want to keep cost down.
I have used similar cable for a similar purpose over longer distances
with no problems, for general purpose "listening" quality. Buying a
higher spec cable is only going to give a very marginal improvement - if
you really are interested in quality, you would link digital ports using
an optical cable and not use analogue, anyway.
--
Sue
| |
| Laurence Payne 2006-04-18, 8:21 pm |
| On Tue, 18 Apr 2006 22:35:53 +0100, Andy <nomail@nomail.com> wrote:
>I would like to take a stereo signal from the line-out of my stereo
>(or TV) to the line-in of my PC.
>
>The equipment is in different rooms and the audio cable would be 10
>metres. It will be this type:
>http://www.maplin.co.uk/images/full/130i0.jpg
>
>I don't understand the technical side but is 10 metres so long that
>it might cause audio problems with things like frequency response or
>voltage/current levels and so on?
>
>Will I need to get some higher specification audio cable to cover
>that distance? I want to keep cost down.
You might get unacceptable noise pickup, you might not. Try. You
might also get hum. Sometimes it responds to simply lifting the
screen connection at one end, sometimes you need an isolating
transformer. Or rather a pair of them.
What's the link for?
| |
| Richard Crowley 2006-04-18, 10:21 pm |
| "Andy" wrote ...
>I am in the UK.
>
> I would like to take a stereo signal from the line-out of my stereo
> (or TV) to the line-in of my PC.
>
> The equipment is in different rooms and the audio cable would be 10
> metres. It will be this type:
> http://www.maplin.co.uk/images/full/130i0.jpg
>
> I don't understand the technical side but is 10 metres so long that
> it might cause audio problems with things like frequency response or
> voltage/current levels and so on?
>
> Will I need to get some higher specification audio cable to cover
> that distance? I want to keep cost down.
The cable is most likely just fine. However beware of
ground loops and other hazards of running audio over
long distances. These have little to do with the cable.
| |
|
| >> Will I need to get some higher specification audio cable to cover that
>
> The cable is most likely just fine. However beware of
> ground loops and other hazards of running audio over
> long distances. These have little to do with the cable.
Expanding on that a little:
My "trans-workshop cable" is about 8 metres long and works perfectly. It's
cheap audio cable (shielded of course).
The equipment on both ends is powered from the same electrical circuit and I
don't have ground loop problems. You would have ground loop problems if the
equipment were powered from different circuits. I gather that you are in
the UK (hence "ring" wiring structure, which I like, instead of the American
daisychain) and that everything is in the same room. It should work fine.
| |
| David Nebenzahl 2006-04-19, 3:21 am |
| mc spake thus:
> I gather that you are in the UK (hence "ring" wiring structure, which
> I like, instead of the American daisychain) and that everything is
> in the same room. It should work fine.
So how does house wiring work in the UK? Is there more than one
grounding ("earthing") point? And how is this better?
(Here, the Merkin practice is to ground the "service panel"--the box
where the big wires come into the house--to a single ground rod, with
everything running downstream from that.)
By the way, this brings up a strange experience I had recently doing
some wiring. I was working for a guy who owns two houses right next to
each other, and he wanted to run a cable TV connection from one house to
the other. I was about to connect the cable in the attic of the house
that was the source of the signal when I got a little tingle. After
grabbing a VOM, it turned out that there was about a 20 volt difference
between the two cable grounds.
Was this due to power line potential differences, or to cable signal
potential differences, or something else? The cable guys do their own
grounding outside, and I don't think they put in any bonds to the
electric service ground. In any case, the whole project was abandoned
then and there as a bad idea. (It occurred to me that a cable
transformer could have solved the problem, but then so could doing the
thing the right way: just getting both houses wired for cable.)
--
Pierre, mon ami. Jetez encore un Scientologiste
dans le baquet d'acide.
- from a posting in alt.religion.scientology titled
"France recommends dissolving Scientologists"
| |
|
| David Nebenzahl wrote:
> mc spake thus:
>
>
>
> So how does house wiring work in the UK? Is there more than one
> grounding ("earthing") point? And how is this better?
>
> (Here, the Merkin practice is to ground the "service panel"--the box
> where the big wires come into the house--to a single ground rod, with
> everything running downstream from that.)
>
> By the way, this brings up a strange experience I had recently doing
> some wiring. I was working for a guy who owns two houses right next to
> each other, and he wanted to run a cable TV connection from one house to
> the other. I was about to connect the cable in the attic of the house
> that was the source of the signal when I got a little tingle. After
> grabbing a VOM, it turned out that there was about a 20 volt difference
> between the two cable grounds.
Mc doesn't understand ground loops. You can get them between two boxes
plugged into the same double socket.
Your tingle was because your equipment is not grounded, and is perfectly normal.
--
Eiron
No good deed ever goes unpunished.
| |
| David Nebenzahl 2006-04-19, 4:21 am |
| Eiron spake thus:
> David Nebenzahl wrote:
>
>
> Mc doesn't understand ground loops. You can get them between two boxes
> plugged into the same double socket.
>
> Your tingle was because your equipment is not grounded, and is perfectly
> normal.
No, my tingle was because I was holding two cables strung between two
different houses, each grounded at its end. Doesn't seem normal at all
to me.
--
Pierre, mon ami. Jetez encore un Scientologiste
dans le baquet d'acide.
- from a posting in alt.religion.scientology titled
"France recommends dissolving Scientologists"
| |
| Don Pearce 2006-04-19, 4:21 am |
| On Tue, 18 Apr 2006 23:32:56 -0700, David Nebenzahl
<nobody@but.us.chickens> wrote:
>Eiron spake thus:
>
>
>No, my tingle was because I was holding two cables strung between two
>different houses, each grounded at its end. Doesn't seem normal at all
>to me.
Most likely the two houses weren't on the same phase of the three
phase supply to the street. Their two grounds could have been doing
very different things voltage-wise. You should always have an
isolation transformer in a connection like this.
d
--
Pearce Consulting
http://www.pearce.uk.com
| |
| David Nebenzahl 2006-04-19, 4:21 am |
| Don Pearce spake thus:
> On Tue, 18 Apr 2006 23:32:56 -0700, David Nebenzahl
> <nobody@but.us.chickens> wrote:
>
>
> Most likely the two houses weren't on the same phase of the three
> phase supply to the street. Their two grounds could have been doing
> very different things voltage-wise. You should always have an
> isolation transformer in a connection like this.
I seriously doubt that, because then the potential would have been more
like 120 volts, right? I think that's grasping at straws: so far as I
know, PG&E (local electricity dealer) doesn't even supply 3-phase to
residential customers. In fact, not even in come commercial districts. I
owned a small business in Berkeley (print shop) until last year, and I
remember the previous owner telling me about all the headaches he had in
having PG&E put in a 3-phase converter (in an underground vault below
the sidewalk outside). So I know that utility lines don't usually carry
3-phase power, except to large industrial customers.
--
Pierre, mon ami. Jetez encore un Scientologiste
dans le baquet d'acide.
- from a posting in alt.religion.scientology titled
"France recommends dissolving Scientologists"
| |
| Don Pearce 2006-04-19, 4:21 am |
| On Tue, 18 Apr 2006 23:49:28 -0700, David Nebenzahl
<nobody@but.us.chickens> wrote:
>Don Pearce spake thus:
>
>
>I seriously doubt that, because then the potential would have been more
>like 120 volts, right? I think that's grasping at straws: so far as I
>know, PG&E (local electricity dealer) doesn't even supply 3-phase to
>residential customers. In fact, not even in come commercial districts. I
>owned a small business in Berkeley (print shop) until last year, and I
>remember the previous owner telling me about all the headaches he had in
>having PG&E put in a 3-phase converter (in an underground vault below
>the sidewalk outside). So I know that utility lines don't usually carry
>3-phase power, except to large industrial customers.
Why would it be 120V? The voltage would depend on how stiff the ground
is round your way. As for three phase supply, no, individual domestic
properties generally don't get that, but streets certainly do - that
is the efficient way to deliver power.
Could be different where you are,of course.
d
--
Pearce Consulting
http://www.pearce.uk.com
| |
| Laurence Payne 2006-04-19, 7:21 am |
| On Tue, 18 Apr 2006 23:49:28 -0700, David Nebenzahl
<nobody@but.us.chickens> wrote:
>I seriously doubt that, because then the potential would have been more
>like 120 volts, right? I think that's grasping at straws: so far as I
>know, PG&E (local electricity dealer) doesn't even supply 3-phase to
>residential customers. In fact, not even in come commercial districts. I
>owned a small business in Berkeley (print shop) until last year, and I
>remember the previous owner telling me about all the headaches he had in
>having PG&E put in a 3-phase converter (in an underground vault below
>the sidewalk outside). So I know that utility lines don't usually carry
>3-phase power, except to large industrial customers.
There'll probably be 3 phases in the street. houses, or groups of
houses will be allocated a single phase.
| |
| tony sayer 2006-04-19, 7:21 am |
| I
>I seriously doubt that, because then the potential would have been more
>like 120 volts, right? I think that's grasping at straws: so far as I
>know, PG&E (local electricity dealer) doesn't even supply 3-phase to
>residential customers. In fact, not even in come commercial districts. I
>owned a small business in Berkeley (print shop) until last year, and I
>remember the previous owner telling me about all the headaches he had in
>having PG&E put in a 3-phase converter (in an underground vault below
>the sidewalk outside). So I know that utility lines don't usually carry
>3-phase power, except to large industrial customers.
>
>
What they tend to do is supply the area with a three phase line at
around 11Kv and transform that down and then supply house number one
with phase one, house two with phase two, three with phase three, four
with phase one, five with phase two, house six with phase three and so
on. Its called load balancing between the phases...
--
Tony Sayer
| |
| Richard Crowley 2006-04-19, 12:21 pm |
| "David Nebenzahl" wrote ...
> No, my tingle was because I was holding two cables strung between two
> different houses, each grounded at its end. Doesn't seem normal at all
> to me.
If they were each properly "grounded", you would NOT
have seen any voltage differential. BY DEFINITION.
(Or else the two houses were on differen planets. :-)
| |
| Richard Crowley 2006-04-19, 12:21 pm |
| "Laurence Payne" wrote...
> There'll probably be 3 phases in the street. houses, or
> groups of houses will be allocated a single phase.
Not in the parts of the USA where I have lived (up and down
the west coast). They break up the 3 phases back at the main
road and supply only one of the phases to each street (or 2-3
streets depending on the load) It is not economical to run all
3 phases along residential (or even small business) areas.
| |
|
| "Richard Crowley" <rcrowley@xpr7t.net> wrote in message
news:124chtja0mkc515@corp.supernews.com...
> "David Nebenzahl" wrote ...
>
> If they were each properly "grounded", you would NOT
> have seen any voltage differential. BY DEFINITION.
I would almost bet that at least one of them wasn't really grounded (to the
earth).
Second choice is that high voltage is being conducted directly into the
earth from some kind of unintended connection. A bad thing.
| |
|
|
"David Nebenzahl" <nobody@but.us.chickens> wrote in message
news:4445d237$0$3693$822641b3@news.adtechcomputers.com...
> mc spake thus:
>
>
> So how does house wiring work in the UK? Is there more than one grounding
> ("earthing") point? And how is this better?
As I understand it, the British ring system is to wire the outlets in a room
in a ring so that each of them has two parallel paths to the point where
power enters the room. As a result, a single high-resistance connection
anywhere in the ring will have almost no effect. That should do a more
reliable job of tying together all the ground connections for the different
pieces of equipment.
| |
|
| "Eiron" <e1ron@hotmail.com> wrote in message
news:4am2f9Fu10fsU1@individual.net...
> Mc doesn't understand ground loops. You can get them between two boxes
> plugged into the same double socket.
Two boxes with 3-wire plugs?
Could you elaborate? I thought a ground loop was due to difference in
potential of the ground connections of 2 different pieces of equipment.
| |
| Don Pearce 2006-04-19, 12:21 pm |
| On Wed, 19 Apr 2006 07:26:25 -0700, "Richard Crowley"
<rcrowley@xpr7t.net> wrote:
>"Laurence Payne" wrote...
>
>Not in the parts of the USA where I have lived (up and down
>the west coast). They break up the 3 phases back at the main
>road and supply only one of the phases to each street (or 2-3
>streets depending on the load) It is not economical to run all
>3 phases along residential (or even small business) areas.
So what do they do when somebody asks for three phase supply? Even a
reasonably small business here in the UK might well do that if their
power needs are significant. The power companies here actually prefer
to supply businesses that way, particularly if they are also careful
about their power factor correction.
Or are zoning laws in the States such that it is not possible to set
up a business in an otherwise residential area?
d
--
Pearce Consulting
http://www.pearce.uk.com
| |
| Don Pearce 2006-04-19, 12:21 pm |
| On Wed, 19 Apr 2006 10:33:13 -0400, "mc"
<look@www.ai.uga.edu.for.address> wrote:
>
>"David Nebenzahl" <nobody@but.us.chickens> wrote in message
>news:4445d237$0$3693$822641b3@news.adtechcomputers.com...
>
>As I understand it, the British ring system is to wire the outlets in a room
>in a ring so that each of them has two parallel paths to the point where
>power enters the room. As a result, a single high-resistance connection
>anywhere in the ring will have almost no effect. That should do a more
>reliable job of tying together all the ground connections for the different
>pieces of equipment.
>
Almost right. The ring actually goes right back to the breaker box,
which is always located where the power enters the house. But the
effect is the same.
d
--
Pearce Consulting
http://www.pearce.uk.com
| |
|
| On 19 Apr 2006, Eiron<e1ron@hotmail.com> wrote:
>
> Mc doesn't understand ground loops. You can get them between two
> boxes plugged into the same double socket.
>
> Your tingle was because your equipment is not grounded, and is
> perfectly normal.
Does your "perfectly normal" mean:
"there is no fault and no danger (until the ground is
actually needed and then will be a danger)"
| |
|
| On 19 Apr 2006, sQuick<squickdrill@hotmail.com> wrote:
> "Andy" <nomail@nomail.com> wrote in message
> news:Xns97A9E5E17D3EE74C1H4@127.0.0.1...
>
> I am using the exact same cable from Maplin, this is to go from
> my computer to my stereo amp.
>
> I would estimate it to be 10m-15m in length and I've had no
> problems with noise.
>
> sQuick..
>
>
Thanks to you and everyone else for the feedback. Seems it is
less of a problem than i was anticipating.
Actually my cable is not exactly the Maplin one I illustarted but
a very similar one.
| |
| gfretwell@aol.com 2006-04-19, 1:21 pm |
| On Wed, 19 Apr 2006 07:22:42 -0700, "Richard Crowley"
<rcrowley@xpr7t.net> wrote:
>"David Nebenzahl" wrote ...
>
>If they were each properly "grounded", you would NOT
>have seen any voltage differential. BY DEFINITION.
>
>(Or else the two houses were on differen planets. :-)
"Ground" is not all created equal. Dirt sucks as a conductor and you
can see significant voltage differences between two grounding
electrode systems. If you are connecting signal lines between two
buildings be sure you also bond the grounding systems together.
| |
| Floyd L. Davidson 2006-04-19, 2:21 pm |
| "mc" <look@www.ai.uga.edu.for.address> wrote:
>"Eiron" <e1ron@hotmail.com> wrote in message
>news:4am2f9Fu10fsU1@individual.net...
>
>
>Two boxes with 3-wire plugs?
>
>Could you elaborate? I thought a ground loop was due to difference in
>potential of the ground connections of 2 different pieces of equipment.
A "ground loop" is caused by having a common ground path for two
different signals. Current from each signal causes a voltage
drop, due to Ohmic losses, across the ground path for both
circuits. The effect is that each circuit affects the signal of
the other. Typically if one of those signals is 60 Hz power and
the other is something in the audio range, the audio signal will
then have a 60 Hz "buzz" on it.
Obviously, if the only ground path is through a common 3-wire
socket, yes it is possible for two boxes to have a ground loop.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
| |
| Floyd L. Davidson 2006-04-19, 2:21 pm |
| "Richard Crowley" <rcrowley@xpr7t.net> wrote:
>"David Nebenzahl" wrote ...
>
>If they were each properly "grounded", you would NOT
>have seen any voltage differential. BY DEFINITION.
>
>(Or else the two houses were on differen planets. :-)
That is not true. Granted that the 20 Volt differential he
mentions in another article is high (for a residential area), it
is not at all uncommon.
What is uncommon though, is a person who can actually feel 20
Volts!
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
| |
| Floyd L. Davidson 2006-04-19, 2:21 pm |
| "mc" <look@www.ai.uga.edu.for.address> wrote:
>"Richard Crowley" <rcrowley@xpr7t.net> wrote in message
>news:124chtja0mkc515@corp.supernews.com...
>
>I would almost bet that at least one of them wasn't really grounded (to the
>earth).
Then there would have been no differential, and hence no voltage and no
tingling... ;-)
>Second choice is that high voltage is being conducted directly into the
>earth from some kind of unintended connection. A bad thing.
Not a bad thing, just a rather common thing in many industrial areas.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
| |
| Floyd L. Davidson 2006-04-19, 2:21 pm |
| donald@pearce.uk.com (Don Pearce) wrote:
>On Wed, 19 Apr 2006 07:26:25 -0700, "Richard Crowley"
><rcrowley@xpr7t.net> wrote:
>
>
>So what do they do when somebody asks for three phase supply? Even a
The above does describe typical residential power distributionn.
However, anywhere that industrial power (i.e., 3 phase) is
available, there will in fact be all three phases available...
>reasonably small business here in the UK might well do that if their
>power needs are significant. The power companies here actually prefer
>to supply businesses that way, particularly if they are also careful
>about their power factor correction.
Same in the US.
>Or are zoning laws in the States such that it is not possible to set
>up a business in an otherwise residential area?
That might be, might not be... it would depend on local laws.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
| |
| Don Pearce 2006-04-19, 2:21 pm |
| On Wed, 19 Apr 2006 09:03:21 -0800, floyd@apaflo.com (Floyd L.
Davidson) wrote:
>"mc" <look@www.ai.uga.edu.for.address> wrote:
>
>A "ground loop" is caused by having a common ground path for two
>different signals. Current from each signal causes a voltage
>drop, due to Ohmic losses, across the ground path for both
>circuits. The effect is that each circuit affects the signal of
>the other. Typically if one of those signals is 60 Hz power and
>the other is something in the audio range, the audio signal will
>then have a 60 Hz "buzz" on it.
>
>Obviously, if the only ground path is through a common 3-wire
>socket, yes it is possible for two boxes to have a ground loop.
You got this backwards. A ground loop is caused by having two ground
paths for a single signal wire. A hum signal is induced into the
signal wire by means of a hum current flowing round that ground loop.
That current can be generated in either of two ways - a simple
potential difference between the two grounds, or alternatively
magnetic induction into the loop; generally the first will generate
the bigger signal.
d
--
Pearce Consulting
http://www.pearce.uk.com
| |
| David Nebenzahl 2006-04-19, 4:21 pm |
| Don Pearce spake thus:
> On Wed, 19 Apr 2006 07:26:25 -0700, "Richard Crowley"
> <rcrowley@xpr7t.net> wrote:
>
>
> So what do they do when somebody asks for three phase supply? Even a
> reasonably small business here in the UK might well do that if their
> power needs are significant. The power companies here actually prefer
> to supply businesses that way, particularly if they are also careful
> about their power factor correction.
Reread my earlier post above. In it I described the situation where a
business I once owned needed to have a power converter installed for
3-phase. This was in Berkeley, in a commercial district, not a
residential one, and I think it's pretty typical of the Bay Area in
general, probably the urban U.S for that matter. The power companies
don't supply 3-phase power even to commercial areas; if someone needs
it, they put in a converter. (We had a printing press that required it.)
Most commercial businesses don't need 3-phase power. Large industrial
customers do.
I think the converters can be shared, so if a couple or a few
neighboring businesses need 3-phase power, they can all use the one
converter.
--
Pierre, mon ami. Jetez encore un Scientologiste
dans le baquet d'acide.
- from a posting in alt.religion.scientology titled
"France recommends dissolving Scientologists"
| |
| Don Pearce 2006-04-19, 4:21 pm |
| On Wed, 19 Apr 2006 11:34:12 -0700, David Nebenzahl
<nobody@but.us.chickens> wrote:
>Don Pearce spake thus:
>
>
>Reread my earlier post above. In it I described the situation where a
>business I once owned needed to have a power converter installed for
>3-phase. This was in Berkeley, in a commercial district, not a
>residential one, and I think it's pretty typical of the Bay Area in
>general, probably the urban U.S for that matter. The power companies
>don't supply 3-phase power even to commercial areas; if someone needs
>it, they put in a converter. (We had a printing press that required it.)
>Most commercial businesses don't need 3-phase power. Large industrial
>customers do.
>
>I think the converters can be shared, so if a couple or a few
>neighboring businesses need 3-phase power, they can all use the one
>converter.
I'm surprised. Just down the road from me there is a small engineering
company - they have a couple of mills, a few lathes and assorted other
machine tools. The power company didn't even ask - they just got three
phase, straight from the street outside.
d
--
Pearce Consulting
http://www.pearce.uk.com
| |
| Floyd L. Davidson 2006-04-19, 5:21 pm |
| donald@pearce.uk.com (Don Pearce) wrote:
>On Wed, 19 Apr 2006 09:03:21 -0800, floyd@apaflo.com (Floyd L.
>Davidson) wrote:
>
>
>You got this backwards.
Actually, what I said was *precisely* correct.
>A ground loop is caused by having two ground
>paths for a single signal wire.
Your language is a mess, but what you just said is *exactly* the
same thing. One wire is a common path...
>A hum signal is induced into the
>signal wire by means of a hum current flowing round that ground loop.
Wrong. There is no loop involved. It is current flowing on the
*common* portion that causes interaction.
>That current can be generated in either of two ways - a simple
>potential difference between the two grounds, or alternatively
>magnetic induction into the loop; generally the first will generate
>the bigger signal.
Get a book or two... and study what happens. Try drawing a diagram
of what you think is happening!
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
| |
| Don Pearce 2006-04-19, 5:21 pm |
| On Wed, 19 Apr 2006 11:23:24 -0800, floyd@apaflo.com (Floyd L.
Davidson) wrote:
>donald@pearce.uk.com (Don Pearce) wrote:
>
>Actually, what I said was *precisely* correct.
>
Nonsense - you claim one ground path and two signals. It is one signal
and two ground paths - it is those two ground paths that form the
ground loop.
>
>Your language is a mess, but what you just said is *exactly* the
>same thing. One wire is a common path...
>
No, my language is just fine, and it is the exact opposite of what you
said.
>
>Wrong. There is no loop involved. It is current flowing on the
>*common* portion that causes interaction.
>
There is a loop involved. That is why it is called a ground loop. The
loop is necessary for the current to flow round and generate the emf
that appears on the signal wire.
>
>Get a book or two... and study what happens. Try drawing a diagram
>of what you think is happening!
Thank you, I have designed a great deal of high precision measuring
equipment and I know exactly what signal paths are present in a ground
loop. And they aren't what you claim.
d
--
Pearce Consulting
http://www.pearce.uk.com
| |
| Floyd L. Davidson 2006-04-19, 5:21 pm |
| David Nebenzahl <nobody@but.us.chickens> wrote:
>Don Pearce spake thus:
>
>
>Reread my earlier post above. In it I described the situation
>where a business I once owned needed to have a power converter
>installed for 3-phase. This was in Berkeley, in a commercial
>district, not a residential one, and I think it's pretty typical
>of the Bay Area in general, probably the urban U.S for that
>matter. The power companies don't supply 3-phase power even to
>commercial areas; if someone needs it, they put in a
>converter. (We had a printing press that required it.) Most
>commercial businesses don't need 3-phase power. Large industrial
>customers do.
>
>I think the converters can be shared, so if a couple or a few
>neighboring businesses need 3-phase power, they can all use the
>one converter.
What is a "converter"? I've never heard of anything described
that way.
Virtually all power is generated as 3-phase...
What you actually get merely depends on what the transformer
arrangement is. Single phase residential power is nothing other
than one phase from a 3 phase distribution system. All that is
required to have 3 phase power is *more wires*!
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
| |
| Floyd L. Davidson 2006-04-19, 5:21 pm |
| donald@pearce.uk.com (Don Pearce) wrote:
>On Wed, 19 Apr 2006 11:23:24 -0800, floyd@apaflo.com (Floyd L.
>Davidson) wrote:
>Nonsense - you claim one ground path and two signals. It is one signal
>and two ground paths - it is those two ground paths that form the
>ground loop.
And I have it *precisely* correct. (Hint: I'm not guessing.)
If there were only one signal... what problem would there be????
The trouble is that one signal causes interference with another.
It does that because they share a common path. Ohmic losses across
that conductor affect *both* signals, even when caused by only one
of them. Bingo, that *is* the problem.
>No, my language is just fine, and it is the exact opposite of what you
>said.
Two ground paths and one wire... does *not* make sense.
Signals have paths. Those paths can be wires. You can't have
two paths in one wire...
But the common "ground loop" is indeed caused by grounding a
single conductor at two points. That provides a common path
through the single wire... for *two* signals. One is the
"desired" signal, and the other is a current between the two
ground points.
>There is a loop involved. That is why it is called a ground loop. The
>loop is necessary for the current to flow round and generate the emf
>that appears on the signal wire.
Try drawing a diagram of what you are describing.
>
>Thank you, I have designed a great deal of high precision measuring
>equipment and I know exactly what signal paths are present in a ground
>loop. And they aren't what you claim.
If you do know what it is, you certainly have a problem
describing it in terms that make sense. I'll vote for you
don't know...
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
| |
|
| mc wrote:
> "Eiron" <e1ron@hotmail.com> wrote in message
> news:4am2f9Fu10fsU1@individual.net...
>
>
>
>
> Two boxes with 3-wire plugs?
>
> Could you elaborate? I thought a ground loop was due to difference in
> potential of the ground connections of 2 different pieces of equipment.
Remember the good old days when everything had a 3-core mains cable?
You could get a ground loop just plugging a tape recorder into an amp.
The bodger's solution was to disconnect the earth in the mains plug
and remember always to connect the audio cable to the amp before connecting
the power. Now everything has 2-core power leads so you get tingles.
--
Eiron
No good deed ever goes unpunished.
| |
| Don Pearce 2006-04-19, 6:21 pm |
| On Wed, 19 Apr 2006 11:46:44 -0800, floyd@apaflo.com (Floyd L.
Davidson) wrote:
>donald@pearce.uk.com (Don Pearce) wrote:
>
>And I have it *precisely* correct. (Hint: I'm not guessing.)
>
>If there were only one signal... what problem would there be????
>The trouble is that one signal causes interference with another.
>It does that because they share a common path. Ohmic losses across
>that conductor affect *both* signals, even when caused by only one
>of them. Bingo, that *is* the problem.
>
So what are you saying here - that a mono signal can't suffer a ground
loop? Stereo is the minimum that can show the problem?
You only need one signal. Here's a hint as to where you may be going
wrong. Signal is the term used to describe the wanted stuff. The rest
isn't signal - it is hum.
>
>Two ground paths and one wire... does *not* make sense.
>Signals have paths. Those paths can be wires. You can't have
>two paths in one wire...
>
Of course it makes sense. The commonest scenario for two ground paths
is that one is the outer of the coax, and the other is a pair of
ground wires in the mains leads, meeting at the mains ground. The
single signal wire is the inner of the coax. This just isn't that hard
to understand.
>But the common "ground loop" is indeed caused by grounding a
>single conductor at two points. That provides a common path
>through the single wire... for *two* signals. One is the
>"desired" signal, and the other is a current between the two
>ground points.
>
No it doesn't. It means that the ground is connected via two separate
paths - you need those two separate paths to form the loop.
>
>Try drawing a diagram of what you are describing.
>
Done. You can find it here http://81.174.169.10/
>
>If you do know what it is, you certainly have a problem
>describing it in terms that make sense. I'll vote for you
>don't know...
No, I think I have described what is going on perfectly - I suspect
the confusion is at your end. It may be simply a semantic confusion
over what constitutes the signal.
d
--
Pearce Consulting
http://www.pearce.uk.com
| |
|
| Andy wrote:
> On 19 Apr 2006, Eiron<e1ron@hotmail.com> wrote:
>
>
>
>
> Does your "perfectly normal" mean:
>
> "there is no fault and no danger (until the ground is
> actually needed and then will be a danger)"
No. It's normal and legal to have a load of double-insulated equipment
connected together so the signal ground is floating at roughly half
mains voltage and can deliver several mA. It's dangerous, in my opinion.
In the UK, with 240v mains, and adjacent houses on different phases,
you might have 220v between the two cables in the attic.
And you can't feel 20v AC unless one end is on your tongue. I just tried it. :-)
--
Eiron
No good deed ever goes unpunished.
| |
| David Nebenzahl 2006-04-19, 6:21 pm |
| Floyd L. Davidson spake thus:
> David Nebenzahl <nobody@but.us.chickens> wrote:
>
>
> What is a "converter"? I've never heard of anything described
> that way.
It's a device--a big, honking piece of electromagnetic equipment--that
generates 3-phase power from 2-phase power. In this case, it sits in an
underground vault beneath the sidewalk, covered by one of them metal plates.
> Virtually all power is generated as 3-phase...
Nope.
> What you actually get merely depends on what the transformer
> arrangement is. Single phase residential power is nothing other
> than one phase from a 3 phase distribution system. All that is
> required to have 3 phase power is *more wires*!
Apparently not. If you don't believe me, ask PG&E (Pacific Greed and
Extortion, as they're known around here). They don't run all 3 wires as
part of their normal power distribution.
I know this thing exists, because I saw the crews working on the damn
thing in front of my shop when it malfunctioned and the press stopped
working.
--
Pierre, mon ami. Jetez encore un Scientologiste
dans le baquet d'acide.
- from a posting in alt.religion.scientology titled
"France recommends dissolving Scientologists"
| |
| David Nebenzahl 2006-04-19, 6:21 pm |
| Eiron spake thus:
> And you can't feel 20v AC unless one end is on your tongue. I just tried
> it. :-)
Some of us may be more sensitive than others. It's a subjective thing,
after all. Believe me, I felt *something*. Being the paranoid
electrician type, I let go of that sucker in a hurry! VOM showed ~20v.
(Dunno whether AC or DC; I'm assuming AC.)
--
Pierre, mon ami. Jetez encore un Scientologiste
dans le baquet d'acide.
- from a posting in alt.religion.scientology titled
"France recommends dissolving Scientologists"
| |
| Don Pearce 2006-04-19, 6:21 pm |
| On Wed, 19 Apr 2006 13:44:48 -0700, David Nebenzahl
<nobody@but.us.chickens> wrote:
>
>Nope.
>
>
>Apparently not. If you don't believe me, ask PG&E (Pacific Greed and
>Extortion, as they're known around here). They don't run all 3 wires as
>part of their normal power distribution.
>
>I know this thing exists, because I saw the crews working on the damn
>thing in front of my shop when it malfunctioned and the press stopped
>working.
>
I'm stunned. This is the first time I've ever heard of power being
generated as anything other than three phase. Apart from anything
else, single phase is mega wasteful of copper.
d
--
Pearce Consulting
http://www.pearce.uk.com
| |
| Arny Krueger 2006-04-19, 6:21 pm |
| "David Nebenzahl" <nobody@but.us.chickens> wrote in message
news:4446a096$0$3692$822641b3@news.adtechcomputers.com
> Floyd L. Davidson spake thus:
>
>
> It's a device--a big, honking piece of electromagnetic
> equipment--that generates 3-phase power from 2-phase
> power. In this case, it sits in an underground vault
> beneath the sidewalk, covered by one of them metal
> plates.
>
> Nope.
>
http://www.kayind.com/basics/why.htm
[color=darkred]
> Apparently not. If you don't believe me, ask PG&E
> (Pacific Greed and Extortion, as they're known around
> here). They don't run all 3 wires as part of their normal
> power distribution.
True for Detroit Edison, as well.
> I know this thing exists, because I saw the crews working
> on the damn thing in front of my shop when it malfunctioned and the
> press stopped working.
http://www.homemetalshopclub.org/pr...onv/phconv.html
| |
| tony sayer 2006-04-19, 7:21 pm |
| In article <444fa13f.393694781@text.usenet.plus.net>, Don Pearce
<donald@pearce.uk.com> writes
>On Wed, 19 Apr 2006 13:44:48 -0700, David Nebenzahl
><nobody@but.us.chickens> wrote:
>
>
>I'm stunned. This is the first time I've ever heard of power being
>generated as anything other than three phase. Apart from anything
>else, single phase is mega wasteful of copper.
>
>d
>
Me too!, virtually every bit of wire string the electricity grid
together in the UK is Three phase. Only in some remote places will you
see overhead High voltage in Single phase, and that only is likely to
serve a signal customer!..
Can't believe the USA is that different?. I know or hear that they have
split centre tapped supplies for 115 and 240 volt domestic supplies...
--
Tony Sayer
| |
| Laurence Payne 2006-04-19, 8:21 pm |
| On Wed, 19 Apr 2006 10:33:13 -0400, "mc"
<look@www.ai.uga.edu.for.address> wrote:
>
>As I understand it, the British ring system is to wire the outlets in a room
>in a ring so that each of them has two parallel paths to the point where
>power enters the room. As a result, a single high-resistance connection
>anywhere in the ring will have almost no effect. That should do a more
>reliable job of tying together all the ground connections for the different
>pieces of equipment.
The electrician re-wiring my house 25 years ago told me ring-mains
were originally developed on battleships. Less chance of localised
damage taking out a load of equipment.
The main advantage in domestic installations was that smaller cable
could be installed for a given power load. With the demise of
electric fires and 15 amp outlets, spur wiring was permissible and
becoming more common.
Earthing seems to be almost as much a black art as is car electrics
:-) I don't pretend to understand it, but apparently changes in the
UK system have introduced stringent new requirements for cross-bonding
all kinds of things that weren't necessary before. Anyone know more
about this?
| |
| Laurence Payne 2006-04-19, 8:21 pm |
| On Wed, 19 Apr 2006 10:33:59 -0400, "mc"
<look@www.ai.uga.edu.for.address> wrote:
>
>Two boxes with 3-wire plugs?
>
>Could you elaborate? I thought a ground loop was due to difference in
>potential of the ground connections of 2 different pieces of equipment.
Different resistance/impendence between different parts of the
equipment and "ground". Whatever that is.
| |
| Roy L. Fuchs 2006-04-20, 1:21 am |
| On Tue, 18 Apr 2006 23:07:30 +0100, Palindr?me <me9@privacy.net> Gave
us:
>Andy wrote:
>
>I have used similar cable for a similar purpose over longer distances
>with no problems, for general purpose "listening" quality. Buying a
>higher spec cable is only going to give a very marginal improvement - if
>you really are interested in quality, you would link digital ports using
>an optical cable and not use analogue, anyway.
Excellent response!
The optical also reduces the number of elements in the run to one
(TOS), or two in the case of speaker feeds.
Heck, there are even speakers that have their amps integrated into
them that take optical feeds. In fact, that is the best manner to
reproduce sound is an amp right next to the acoustical transducer.
One doesn't need crossover networks in one's speaker if each driver
has its own amplifier. Just massage the corners a bit.
| |
| Roy L. Fuchs 2006-04-20, 1:21 am |
| On Wed, 19 Apr 2006 10:34:58 +0100, tony sayer <tony@bancom.co.uk>
Gave us:
>I
>
>What they tend to do is supply the area with a three phase line at
>around 11Kv and transform that down and then supply house number one
>with phase one, house two with phase two, three with phase three, four
>with phase one, five with phase two, house six with phase three and so
>on. Its called load balancing between the phases...
Here, the pole transformer secondary (service side) is a center
tapped 240 volt output (there are buck and boost taps on some).
Homes here get the full 240 with the centertap (neutral), and within
the home, it is routed about as a single side hot-to-centertap, 120
volt run. The oven, furnace, dryer, inline hot water, etc (high power
devices) typically gets the full center tapped 240 feed. The center
tap is ground at the service panel with a ground rod, and all fault
returns (third wire) also come back to this grounded terminal bus.
All the 240 volt branches get dual breakers and all the 120 volt runs
get a breaker installed on that side of the service panel it will be
drawing from.
That makes any single run in the house 120 volts from ground (or
neutral).
Anyway, the pole transformer feeds several (4?) houses, then another
transformer is used for the next quad of houses The HV feed at the
top of the power distribution poles in Ohio was like 11kV IIRC (not
sure), and I don't know if it was 3 phase or not. I do know that our
3 phase is not like California's. They are Delta. I think Ohio is
Wye.
They may balance their consumption by sending a different phase to
an entire neighborhood, and another to the next neighborhood down the
way. Seems costly to do it house by house by house as you say is the
case where you are.
| |
| Roy L. Fuchs 2006-04-20, 1:21 am |
| On Wed, 19 Apr 2006 10:33:59 -0400, "mc"
<look@www.ai.uga.edu.for.address> Gave us:
>"Eiron" <e1ron@hotmail.com> wrote in message
>news:4am2f9Fu10fsU1@individual.net...
>
>
>Two boxes with 3-wire plugs?
>
>Could you elaborate? I thought a ground loop was due to difference in
>potential of the ground connections of 2 different pieces of equipment.
>
If it were two separate circuits, would it not make sense to think
that there would be a small chaotic potential to be read across them?
| |
| Roy L. Fuchs 2006-04-20, 1:21 am |
| On Wed, 19 Apr 2006 17:02:04 +0100, Andy <nomail@nomail.com> Gave us:
>On 19 Apr 2006, sQuick<squickdrill@hotmail.com> wrote:
>
>
>Thanks to you and everyone else for the feedback. Seems it is
>less of a problem than i was anticipating.
>
>Actually my cable is not exactly the Maplin one I illustarted but
>a very similar one.
Uh oh... all bets are off... ;-]
Till we see that new photo posted.
| |
| Roy L. Fuchs 2006-04-20, 1:21 am |
| On Wed, 19 Apr 2006 12:12:25 -0400, gfretwell@aol.com Gave us:
>On Wed, 19 Apr 2006 07:22:42 -0700, "Richard Crowley"
><rcrowley@xpr7t.net> wrote:
>
>
>"Ground" is not all created equal. Dirt sucks as a conductor and you
>can see significant voltage differences between two grounding
>electrode systems. If you are connecting signal lines between two
>buildings be sure you also bond the grounding systems together.
Reminds me of an ESD fiasco I had at one place I fixed up while I
worked there.
We drove a ground rod in the shop, into the earth at a little
breakout point in the slab of our floor.
The potential between the grounded benches and the AC system
grounded SMD reflow bench was 90 volts. Enough that I could feel the
tinge in my arms if I rested them on the mat for that bench. That
shop was in sad shape.
| |
| Roy L. Fuchs 2006-04-20, 1:21 am |
| On Wed, 19 Apr 2006 11:46:44 -0800, floyd@apaflo.com (Floyd L.
Davidson) Gave us:
>But the common "ground loop" is indeed caused by grounding a
>single conductor at two points. That provides a common path
>through the single wire... for *two* signals. One is the
>"desired" signal, and the other is a current between the two
>ground points.
His eyes should begin to open right about here.
| |
| Don Pearce 2006-04-20, 3:21 am |
| On Wed, 19 Apr 2006 23:48:39 +0100, Laurence Payne
<lpayneNOSPAM@dslDOTpipexDOTcom> wrote:
>On Wed, 19 Apr 2006 10:33:13 -0400, "mc"
><look@www.ai.uga.edu.for.address> wrote:
>
>
>The electrician re-wiring my house 25 years ago told me ring-mains
>were originally developed on battleships. Less chance of localised
>damage taking out a load of equipment.
>
>The main advantage in domestic installations was that smaller cable
>could be installed for a given power load. With the demise of
>electric fires and 15 amp outlets, spur wiring was permissible and
>becoming more common.
>
>Earthing seems to be almost as much a black art as is car electrics
>:-) I don't pretend to understand it, but apparently changes in the
>UK system have introduced stringent new requirements for cross-bonding
>all kinds of things that weren't necessary before. Anyone know more
>about this?
Essentially everything metallic that is a fixture within a house must
be bonded to mains ground. This includes everything in the plumbing
system - sinks, bathtub etc.
The ground wires for the ring mains just follow along with the power
wires and ground all the metal outlet and switch boxes,
d
--
Pearce Consulting
http://www.pearce.uk.com
| |
| David Nebenzahl 2006-04-20, 4:21 am |
| tony sayer spake thus:
> In article <444fa13f.393694781@text.usenet.plus.net>, Don Pearce
> <donald@pearce.uk.com> writes
>
>
> Me too!, virtually every bit of wire string the electricity grid
> together in the UK is Three phase. Only in some remote places will you
> see overhead High voltage in Single phase, and that only is likely to
> serve a signal customer!..
>
> Can't believe the USA is that different?. I know or hear that they have
> split centre tapped supplies for 115 and 240 volt domestic supplies...
Yes, what's so strange about that? We get three wires coming into our
houses: one neutral and two hots. The hots are each 120 (nominally) with
respect to the neutral, with 240 between the hots.
--
Pierre, mon ami. Jetez encore un Scientologiste
dans le baquet d'acide.
- from a posting in alt.religion.scientology titled
"France recommends dissolving Scientologists"
| |
| Floyd L. Davidson 2006-04-20, 5:21 am |
| donald@pearce.uk.com (Don Pearce) wrote:
>On Wed, 19 Apr 2006 11:46:44 -0800, floyd@apaflo.com (Floyd L.
>Davidson) wrote:
>Done. You can find it here http://81.174.169.10/
I meant a diagram that *explained* what a ground loop is. Your
diagram does nothing, and isn't even a electrical diagram, much
less one of a ground loop circuit. Here is the electrical
equivalent diagram for your "ground loop",
Desired
Signal Source
o o
| |
| +-------+
| | Rload |
| +-------+
| |
| +-------> connection =======//======= <------+
| | to cable (Induced Signal) |
| +-------+ shield |
| | Rgrnd | |
| +-------+ |
| | |
+------+ <--------- Ground Differential ----------> |
| (Signal Source) |
----- Earth Earth -----
--- Ground Ground ---
- -
There are two resistors (Rload and Rgrnd) with one desired
signal source and two others that affect the voltage drop
across the resistors.
It is easier to see what happens if we assume the "desired
signal" is a current limited (i.e., high impedance) source.
In addition to the "desired signal" sources, there would also
be currents induced into the cable shield by external fields,
and currents induced by ground differential voltages.
All currents contribute to the voltage across Rgrnd. The
voltage across Rload is affected by the voltage across Rgrnd,
and thus the voltage drop across Rload.
Current through the shield affecting the voltage across Rload is
noise. If that is significant, it is commonly said to be a
"ground loop".
Lifting the ground from one side of the cable shield will stop
the current flow, and thus "cure" the problem. However,
reducing the resistance of Rgrnd, the common ground wire would
have the same effect.
Hence you have two choices. One is very easy and has no
detrimental effects for short cables inside a building that
has both ends on the same AC power distribution and a common
ground or very low potential difference between two earth
grounds.
Note that long runs of comm cable do not fit that description,
and therefore use the technique allowing only *very* *low*
*impedance* common ground connections. (The only common part
has to be a large, low impedance, cable that is preferably
short.)
What does that mean in practice? Here is another version of
your "diagram", except of course this one actually *is*
an electrical diagram.
+-------+ +-------+
| | | |
| EQUIP | <------- signal wire/pair -------< | EQUIP |
| | ========= cable shield ========= | |
+-------+ | | +-------+
| | | | | |
| +---+ +---+ |
| |
| |
----- Earth ----- Earth
--- Ground --- Ground
- -
This typically results in a ground loop *if* the size of the
two wires from the EQUIP to Earth Ground is not large enough to
provide a very low impedance (which is difficult to do if the
wires are any length at all, such as if the path to Earth Ground
is provided by AC power wiring for the building).
As noted, there are two solutions, the most well known is to
simply remove the ground connection to one side of the shielded
cable.
But the expedient of removing the ground at one end accomplishes
several things in addition to eliminating the ground loop. It
also removes common mode DC equalization, and it eliminates
induced current flow in the cable shield thus preventing that
current from reducing common mode noise induction in the signal
wires for balanced circuits.
Note that this is appropriate for use with cable existing
within a single building. The benefit is the same, but the
negatives are of negligible effect.
+-------+ +-------+
| | | |
| EQUIP | <------- signal wire/pair -------< | EQUIP |
| | ========= cable shield ========= | |
+-------+ | +-------+
| | | |
| +---+ <-- Single ground for shield |
| |
| |
----- Earth ----- Earth
--- Ground --- Ground
- -
However, if the cable is a long run, and particularly if there
is exposure to power lines, if the ground potential is different
at the two ends, or if there are any other sources of induced
noise in the cable, this arrangement has the best effect:
+-------+ +-------+
| | | |
| EQUIP | <------- signal wire/pair -------< | EQUIP |
| | ========= cable shield ========= | |
+-------+ | | +-------+
| | | |
| | <-- separate grounds --> | |
o------+ +------o
* *
* <-- low impedance ground connections --> *
* *
----- Earth ----- Earth
--- Ground --- Ground
- -
Note the minimum common path to ground. If correctly sized
there will be no significant voltage drop across that small
section. (Which is to say, that conductor should probably be
copper strap between a copper terminal plate and the actual
ground system connection.)
Hence, there is no "ground loop" effect. However, the two
grounds are connected electrically and the voltage is equalized
between then. The second benefit is that voltages induced into
the cable by exposure to external fields will have a low
impedance circuit path, and therefore will conduct current.
>No, I think I have described what is going on perfectly - I suspect
>the confusion is at your end. It may be simply a semantic confusion
>over what constitutes the signal.
I highly suspect that you will have a number of questions about
the above. Note that it is not semantic confusion, and that this
is a topic I've taught before. Please feel free to ask "What the
Hellll does that mean?" about any part of it you like.
Just keep in mind that it is *precisely* *correct*. I may not
have gone into enough detail, or used words that clearly paint
the right picture in the mind of any given reader though, so
questions that cause the description to be restated in different
ways are guaranteed to be helpful.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
| |
| tony sayer 2006-04-20, 5:21 am |
| In article <44472ec1$0$3686$822641b3@news.adtechcomputers.com>, David
Nebenzahl <nobody@but.us.chickens> writes
>tony sayer spake thus:
>
>
>Yes, what's so strange about that? We get three wires coming into our
>houses: one neutral and two hots. The hots are each 120 (nominally) with
>respect to the neutral, with 240 between the hots.
>
>
Thats not strange as such, just the general lack of 3 phase
distribution.
Why do you still use 115-120 supplies what with the extra current
demands, or is there still a perceived electric shock issue?.....
--
Tony Sayer
| |
| tony sayer 2006-04-20, 5:21 am |
| In article <b70e42h1s2chs6q9bn5vl52rtghco3r05t@4ax.com>, Roy L. Fuchs
<roylfuchs@urfargingicehole.org> writes
>On Wed, 19 Apr 2006 10:34:58 +0100, tony sayer <tony@bancom.co.uk>
>Gave us:
>
>
>
> Here, the pole transformer secondary (service side) is a center
>tapped 240 volt output (there are buck and boost taps on some).
>
> Homes here get the full 240 with the centertap (neutral), and within
>the home, it is routed about as a single side hot-to-centertap, 120
>volt run. The oven, furnace, dryer, inline hot water, etc (high power
>devices) typically gets the full center tapped 240 feed. The center
>tap is ground at the service panel with a ground rod, and all fault
>returns (third wire) also come back to this grounded terminal bus.
>
>All the 240 volt branches get dual breakers and all the 120 volt runs
>get a breaker installed on that side of the service panel it will be
>drawing from.
>
>That makes any single run in the house 120 volts from ground (or
>neutral).
>
> Anyway, the pole transformer feeds several (4?) houses, then another
>transformer is used for the next quad of houses The HV feed at the
>top of the power distribution poles in Ohio was like 11kV IIRC (not
>sure), and I don't know if it was 3 phase or not. I do know that our
>3 phase is not like California's. They are Delta. I think Ohio is
>Wye.
>
> They may balance their consumption by sending a different phase to
>an entire neighborhood, and another to the next neighborhood down the
>way. Seems costly to do it house by house by house as you say is the
>case where you are.
Thanks for that enlightening post. It may well be that we don't have the
centre tapped supply arrangement. In the local substation Y arranged,
the centre is earth connected and referred to as the Neutral return and
each phase is then carried on a three conductor cable with the wire
armouring used as the neutral return and its also connected as the
safety earth.
as strange as that may seem;).....
--
Tony Sayer
| |
| Don Pearce 2006-04-20, 5:21 am |
| On Wed, 19 Apr 2006 23:30:25 -0800, floyd@apaflo.com (Floyd L.
Davidson) wrote:
>donald@pearce.uk.com (Don Pearce) wrote:
>
>I meant a diagram that *explained* what a ground loop is. Your
>diagram does nothing, and isn't even a electrical diagram, much
>less one of a ground loop circuit. Here is the electrical
>equivalent diagram for your "ground loop",
>
> Desired
> Signal Source
>
> o o
> | |
> | +-------+
> | | Rload |
> | +-------+
> | |
> | +-------> connection =======//======= <------+
> | | to cable (Induced Signal) |
> | +-------+ shield |
> | | Rgrnd | |
> | +-------+ |
> | | |
> +------+ <--------- Ground Differential ----------> |
> | (Signal Source) |
> ----- Earth Earth -----
> --- Ground Ground ---
> - -
>
Mine isn't even an electrical diagram? At least it had the load at the
right end of the cable. You have put it at the same end as the source.
This is just nonsense.
>There are two resistors (Rload and Rgrnd) with one desired
>signal source and two others that affect the voltage drop
>across the resistors.
>
>It is easier to see what happens if we assume the "desired
>signal" is a current limited (i.e., high impedance) source.
>
>In addition to the "desired signal" sources, there would also
>be currents induced into the cable shield by external fields,
>and currents induced by ground differential voltages.
>
>All currents contribute to the voltage across Rgrnd. The
>voltage across Rload is affected by the voltage across Rgrnd,
>and thus the voltage drop across Rload.
>
>Current through the shield affecting the voltage across Rload is
>noise. If that is significant, it is commonly said to be a
>"ground loop".
>
>Lifting the ground from one side of the cable shield will stop
>the current flow, and thus "cure" the problem. However,
>reducing the resistance of Rgrnd, the common ground wire would
>have the same effect.
>
>Hence you have two choices. One is very easy and has no
>detrimental effects for short cables inside a building that
>has both ends on the same AC power distribution and a common
>ground or very low potential difference between two earth
>grounds.
>
>Note that long runs of comm cable do not fit that description,
>and therefore use the technique allowing only *very* *low*
>*impedance* common ground connections. (The only common part
>has to be a large, low impedance, cable that is preferably
>short.)
>
Why are you telling me this?
>What does that mean in practice? Here is another version of
>your "diagram", except of course this one actually *is*
>an electrical diagram.
>
> +-------+ +-------+
> | | | |
> | EQUIP | <------- signal wire/pair -------< | EQUIP |
> | | ========= cable shield ========= | |
> +-------+ | | +-------+
> | | | | | |
> | +---+ +---+ |
> | |
> | |
> ----- Earth ----- Earth
> --- Ground --- Ground
> - -
>
No more so than mine.
>
>This typically results in a ground loop *if* the size of the
>two wires from the EQUIP to Earth Ground is not large enough to
>provide a very low impedance (which is difficult to do if the
>wires are any length at all, such as if the path to Earth Ground
>is provided by AC power wiring for the building).
>
>As noted, there are two solutions, the most well known is to
>simply remove the ground connection to one side of the shielded
>cable.
>
>But the expedient of removing the ground at one end accomplishes
>several things in addition to eliminating the ground loop. It
>also removes common mode DC equalization, and it eliminates
>induced current flow in the cable shield thus preventing that
>current from reducing common mode noise induction in the signal
>wires for balanced circuits.
>
Common mode DC equalization? What has DC to do with any of this, and
what do you mean by equalization.
Are you still insisting that in a ground loop there are two signal
connections and one ground connection?
>Note that this is appropriate for use with cable existing
>within a single building. The benefit is the same, but the
>negatives are of negligible effect.
>
> +-------+ +-------+
> | | | |
> | EQUIP | <------- signal wire/pair -------< | EQUIP |
> | | ========= cable shield ========= | |
> +-------+ | +-------+
> | | | |
> | +---+ <-- Single ground for shield |
> | |
> | |
> ----- Earth ----- Earth
> --- Ground --- Ground
> - -
>
>However, if the cable is a long run, and particularly if there
>is exposure to power lines, if the ground potential is different
>at the two ends, or if there are any other sources of induced
>noise in the cable, this arrangement has the best effect:
>
> +-------+ +-------+
> | | | |
> | EQUIP | <------- signal wire/pair -------< | EQUIP |
> | | ========= cable shield ========= | |
> +-------+ | | +-------+
> | | | |
> | | <-- separate grounds --> | |
> o------+ +------o
> * *
> * <-- low impedance ground connections --> *
> * *
> ----- Earth ----- Earth
> --- Ground --- Ground
> - -
>
What do you mean by separate grounds? Separate from what? You have
grounded the equipment at each end, and also connected them by the
cable shield. This forms a ground loop and cures nothing.
>Note the minimum common path to ground. If correctly sized
>there will be no significant voltage drop across that small
>section. (Which is to say, that conductor should probably be
>copper strap between a copper terminal plate and the actual
>ground system connection.)
>
>Hence, there is no "ground loop" effect. However, the two
>grounds are connected electrically and the voltage is equalized
>between then. The second benefit is that voltages induced into
>the cable by exposure to external fields will have a low
>impedance circuit path, and therefore will conduct current.
>
>
>I highly suspect that you will have a number of questions about
>the above. Note that it is not semantic confusion, and that this
>is a topic I've taught before. Please feel free to ask "What the
>Hellll does that mean?" about any part of it you like.
>
>Just keep in mind that it is *precisely* *correct*. I may not
>have gone into enough detail, or used words that clearly paint
>the right picture in the mind of any given reader though, so
>questions that cause the description to be restated in different
>ways are guaranteed to be helpful.
No, the thread has effectively been killed by your diagrams that won't
survive the threading process, and are hence not discussable in any
meaningful way.
If you want to carry on believing that a ground loop needs two signal
paths and one ground path, I am happy to leave you to it.
d
--
Pearce Consulting
http://www.pearce.uk.com
| |
| Jim Lesurf 2006-04-20, 10:21 am |
| In article <Xns97A9E5E17D3EE74C1H4@127.0.0.1>, Andy
<nomail@nomail.com>
wrote:
> I am in the UK.
> I would like to take a stereo signal from the line-out of my stereo (or
> TV) to the line-in of my PC.
> The equipment is in different rooms and the audio cable would be 10
> metres. It will be this type:
> http://www.maplin.co.uk/images/full/130i0.jpg
> I don't understand the technical side but is 10 metres so long that it
> might cause audio problems with things like frequency response or
> voltage/current levels and so on?
> Will I need to get some higher specification audio cable to cover that
> distance? I want to keep cost down.
To be able to give a complete answer we would need to know the output
impedance values for your stereo and TV.
The output impedance (resistance) will tend to combine with the cable
capacitance to make an RC low-pass filter. This may or may not matter, but
to estimate the effect we'd need to relevant values.
Slainte,
Jim
--
Electronics http://www.st-and.ac.uk/~www_pa/Sco...ro/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html
| |
| Arny Krueger 2006-04-20, 10:21 am |
| "tony sayer" <tony@bancom.co.uk> wrote in message
news:cU50b9BY8qREFwBA@bancom.co.uk
> In article <444fa13f.393694781@text.usenet.plus.net>, Don
> Pearce <donald@pearce.uk.com> writes
> Me too!, virtually every bit of wire string the
> electricity grid together in the UK is Three phase. Only
> in some remote places will you see overhead High voltage
> in Single phase, and that only is likely to serve a
> signal customer!..
>
> Can't believe the USA is that different?. I know or hear
> that they have split centre tapped supplies for 115 and
> 240 volt domestic supplies...
All true. It's called "legacy technology". Unlike Europe, the US missed
out on the cleansing benefits of being the site of a world war.
| |
| Arny Krueger 2006-04-20, 10:21 am |
| "tony sayer" <tony@bancom.co.uk> wrote in message
news:7NGtt2CkpzREFw1a@bancom.co.uk
> Why do you still use 115-120 supplies what with the extra
> current demands, or is there still a perceived electric
> shock issue?.....
Most US factories that use substantial amounts of power use 3 phase. It's
mostly just the residential areas and isolated light industrial areas that
lack it.
Electric power use per capita in the US is closer to being uniform or
decreasing, as opposed to there being extra current demands.
http://www.eia.doe.gov/emeu/25opec/sld020.htm
http://www.aceee.org/energy/effact.htm
"Total primary energy use per capita in the United States in 2000 was almost
identical to that in 1973. Over the same 27-year period economic output
(GDP) per capita increased 74 percent"
Since 2001 or so, there has been a major conversion of existing residential
lighting to compact fluorescent bulbs which produce about 3 times as much
light per watt.
| |
| Palindr☻me 2006-04-20, 10:21 am |
| Jim Lesurf wrote:
> In article <Xns97A9E5E17D3EE74C1H4@127.0.0.1>, Andy
> <nomail@nomail.com>
> wrote:
>
>
>
>
>
>
>
>
>
>
>
>
> To be able to give a complete answer we would need to know the output
> impedance values for your stereo and TV.
>
> The output impedance (resistance) will tend to combine with the cable
> capacitance to make an RC low-pass filter. This may or may not matter, but
> to estimate the effect we'd need to relevant values.
>
A quick bit of mental arithmetic, with the sort of distances and cables
mentioned by the OP, gives me an estimate of around 5k output impedance,
or greater, before it should give a noticeable effect (OK, a bit lower
if you can hear and are concerned about getting >10kHz stuff). I haven't
come across a line out with a higher impedance than 5k, so I don't think
it is going to be a problem.
Even so, this can be compensated for by a tweak of the tone controls on
the PC.
--
Sue
| |
|
| > Why do you still use 115-120 supplies what with the extra current
> demands, or is there still a perceived electric shock issue?.....
At this point, changing voltages would be prohibitively expensive. We do
have 240-volt outlets for major appliances.
It's a trade-off. 120 V is safer from the electric shock standpoint, but
240 V greatly reduces the risk of starting a fire when a connection develops
high resistance, since there will be only half as much current and thus 1/4
as much heat output. British ring wiring further reduces that risk. I
wonder if ring wiring is legal in the US... if so, I might request it the
next time I have something wired.
| |
|
| >> To be able to give a complete answer we would need to know the output
>
> A quick bit of mental arithmetic, with the sort of distances and cables
> mentioned by the OP, gives me an estimate of around 5k output impedance,
> or greater, before it should give a noticeable effect (OK, a bit lower if
> you can hear and are concerned about getting >10kHz stuff). I haven't come
> across a line out with a higher impedance than 5k, so I don't think it is
> going to be a problem.
The output impedance of any modern IC-based audio equipment is probably
going to be quite low (under 100 ohms) because the output impedance of an
op-amp is inherently low. This includes line-level outputs that are
intended to drive high-impedance inputs.
| |
| Floyd L. Davidson 2006-04-20, 1:21 pm |
| Laurence Payne <lpayneNOSPAM@dslDOTpipexDOTcom> wrote:
>On Wed, 19 Apr 2006 10:33:59 -0400, "mc"
><look@www.ai.uga.edu.for.address> wrote:
>
>
>Different resistance/impendence between different parts of the
>equipment and "ground". Whatever that is.
Differing impedances is harmless. The problem is *common* impedances.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
| |
| Floyd L. Davidson 2006-04-20, 1:21 pm |
| donald@pearce.uk.com (Don Pearce) wrote:
>On Wed, 19 Apr 2006 23:30:25 -0800, floyd@apaflo.com (Floyd L.
>Davidson) wrote:
>Mine isn't even an electrical diagram? At least it had the load at the
>right end of the cable. You have put it at the same end as the source.
>This is just nonsense.
My appologies, I didn't mean to go that far over your head.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
| |
| Roy L. Fuchs 2006-04-21, 1:21 am |
| On Thu, 20 Apr 2006 07:54:57 GMT, donald@pearce.uk.com (Don Pearce)
Gave us:
>No, the thread has effectively been killed by your diagrams that won't
>survive the threading process, and are hence not discussable in any
>meaningful way.
You just proved that you are even more of an idiot than he proved
you are.
His diagrams didn't kill the thread, and no, you do NOT quote
everything over and over again, dolt boy.
| |
| Don Pearce 2006-04-21, 4:21 am |
| On Fri, 21 Apr 2006 03:46:32 GMT, Roy L. Fuchs
<roylfuchs@urfargingicehole.org> wrote:
>On Thu, 20 Apr 2006 07:54:57 GMT, donald@pearce.uk.com (Don Pearce)
>Gave us:
>
>
> You just proved that you are even more of an idiot than he proved
>you are.
>
> His diagrams didn't kill the thread, and no, you do NOT quote
>everything over and over again, dolt boy.
I quote what I want to quote. I produced a simple diagram that showed
the essentials of a ground loop - two ground connections and a single
signal connection. This was the opposite of what he claimed. He then
went on to produce a slew of poor ascii diagrams, none of which
demonstrated his contention. It was clear at that point that the
thread was going nowhere.
So, are you saying he is right, and I am wrong? Do you believe that
for a ground loop you need two signal connections and one ground
connection?
Go ahead - make my day.
d
--
Pearce Consulting
http://www.pearce.uk.com
| |
| Floyd L. Davidson 2006-04-21, 6:21 am |
| donald@pearce.uk.com (Don Pearce) wrote:
>On Fri, 21 Apr 2006 03:46:32 GMT, Roy L. Fuchs
><roylfuchs@urfargingicehole.org> wrote:
>
>
>I quote what I want to quote. I produced a simple diagram that showed
>the essentials of a ground loop - two ground connections and a single
>signal connection. This was the opposite of what he claimed. He then
>went on to produce a slew of poor ascii diagrams, none of which
>demonstrated his contention. It was clear at that point that the
>thread was going nowhere.
You produced a _block_ diagram, not a circuit diagram. You did
not demonstrate that it even produced a ground loop, and in fact
what you showed does *not* necessarily constitute a ground loop.
>So, are you saying he is right, and I am wrong? Do you believe that
>for a ground loop you need two signal connections and one ground
>connection?
>
>Go ahead - make my day.
You still can't get the right quote. Two signals, one common path.
There need not be a ground, and there need not be a loop.
And you can trust that everyone who actually does understand what
happens is indeed saying you are wrong.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
| |
| Don Pearce 2006-04-21, 6:21 am |
| On Fri, 21 Apr 2006 00:33:35 -0800, floyd@apaflo.com (Floyd L.
Davidson) wrote:
>donald@pearce.uk.com (Don Pearce) wrote:
>
>You produced a _block_ diagram, not a circuit diagram. You did
>not demonstrate that it even produced a ground loop, and in fact
>what you showed does *not* necessarily constitute a ground loop.
>
The diagram demonstrated exactly what it needed to demonstrate - no
more and no less. To get a ground loop, you need to make a loop from
the ground. To make a loop, you need the ground from one piece of kit
to another by two separate paths. This can be a problem in two ways.
Either, if the loop is physically large it can intercept magnetic hum
fields and generate a casement flowing around the loop, or if other
equipment is using the circuit, those currents flowing through the
main ground path will do the job for you.
The mechanism that turns these currents into emfs that actually couple
into the input was irrelevant to the point I was making. I was showing
that for a ground loop, you actually need to make a loop from the
ground.
You diagrams, on the other hand were actually wrong. You were putting
Earth symbols at locations where there is no Earth connection. In a
house there is only one Earth connection, and that is on the company
side of the consumer unit. All ground connections within the house are
as I showed - simple wire connections between pieces of kit. In fact,
the Earth connection is irrelevant to the phenomenon - ground loops
would still happen if the whole lot were floating.
Maybe I'm wrong of course - in your house does each mains socket have
an individual ground which is actually a stake driven into the Earth?
No? Didn't think so.
>
>You still can't get the right quote. Two signals, one common path.
>There need not be a ground, and there need not be a loop.
>
Wrong - as wrong as you can get. Let me tell you this again. You can
have ground loops producing hum in a mono system. That is just one
signal in case counting is a problem. What you need is the two ground
connections. (Two is one more than one).
>And you can trust that everyone who actually does understand what
>happens is indeed saying you are wrong.
I leave them to judge.
d
--
Pearce Consulting
http://www.pearce.uk.com
| |
| Stacia 2006-04-21, 7:21 am |
| floyd@apaflo.com (Floyd L. Davidson) writes:
>A "ground loop" is caused by having a common ground path for two
>different signals. Current from each signal causes a voltage
>drop, due to Ohmic losses, across the ground path for both
>circuits. The effect is that each circuit affects the signal of
>the other. Typically if one of those signals is 60 Hz power and
>the other is something in the audio range, the audio signal will
>then have a 60 Hz "buzz" on it.
I'm a complete newbie when it comes to this stuff, so I'm jumping in
with a question and hoping I'm in the right place.
We have always hooked up our computer (in one room) to our stereo (in
another) so we can play audio from the computer through the stereo
speakers. We recently moved and in this new house we're getting a hum
or buzz on the line when we play music from the computer. The cable
from computer to stereo is 30 feet and there was no hum in the audio
when we did this in our previous house.
What can we do to get rid of the hum? We've tried physically moving
the cable but that hasn't changed anything.
Thanks,
Stacia
| |
| Palindr☻me 2006-04-21, 7:21 am |
| Stacia wrote:
> floyd@apaflo.com (Floyd L. Davidson) writes:
>
>
>
>
> I'm a complete newbie when it comes to this stuff, so I'm jumping in
> with a question and hoping I'm in the right place.
> We have always hooked up our computer (in one room) to our stereo (in
> another) so we can play audio from the computer through the stereo
> speakers. We recently moved and in this new house we're getting a hum
> or buzz on the line when we play music from the computer. The cable
> from computer to stereo is 30 feet and there was no hum in the audio
> when we did this in our previous house.
> What can we do to get rid of the hum? We've tried physically moving
> the cable but that hasn't changed anything.
>
Use Toslink optical cable to link the two, assuming that the two have
suitable ports.
--
Sue
| |
| Floyd L. Davidson 2006-04-21, 7:21 am |
| donald@pearce.uk.com (Don Pearce) wrote:
>The diagram demonstrated exactly what it needed to demonstrate - no
>more and no less. To get a ground loop, you need to make a loop from
>the ground. To make a loop, you need the ground from one piece of kit
>to another by two separate paths. This can be a problem in two ways.
>Either, if the loop is physically large it can intercept magnetic hum
>fields and generate a casement flowing around the loop, or if other
>equipment is using the circuit, those currents flowing through the
>main ground path will do the job for you.
Virtually *every* outside plant telephone cable is wired up
exactly like that. There is a ground at both ends of each and
every section (3000 or 6000 feet), and the shields from each
coupled section are bonded to the other and to ground.
A three mile long section of cable might look just like this:
6000' 6000' 6000'
<-----------o----------o-----------> signal pair
<-----------o----------o----------->
+==//==+ +==//==+ +==//==+ shield
| | | | | |
| +-+-+ +-+-+ |
| | | |
----- ----- ----- -----
--- --- --- ---
- - - -
Yet there is no ground loop, ever. Your description says that would
virtually *always* cause a ground loop.
The problem is that you description does *NOT* describe the essence of
a "ground loop". You have not shown where the coupling takes place, nor
have you describe why it happens.
You apparently were unable to read the equivalent electrical diagram
that I posted showing exactly what the mechanism is. Here is is again,
though this time I've rearranged it slightly to meet your requirement
that the load resister be to the right of the input. I hope the irony
of the difference is not lost on you...
o---------+
|
+-------+
| Rload |
+-------+
Signal |
Source +-------> connection =======//======= <------+
| to cable (Induced Signal) |
+-------+ shield |
| Rgrnd | |
+-------+ |
| |
o---------+ <--------- Ground Differential ----------> |
| (Signal Source) |
----- Earth Earth -----
--- Ground Ground ---
- -
>The mechanism that turns these currents into emfs that actually couple
>into the input was irrelevant to the point I was making. I was showing
>that for a ground loop, you actually need to make a loop from the
>ground.
You do *not* need a loop, and the "mechanism ... that actually
couple" them *is* the only point that actually matters. If
there is no interference, then there is no "ground loop". When
there is interference, that mechanism is what causes it.
The mechanism is having a single common path for two different
signals. (It often involves a ground system and that might well
have a loop, but in fact is there is no requirement for it to
be a ground system and no loop is required other than the normal
closed circuit required by *every* signal path.)
>You diagrams, on the other hand were actually wrong. You were putting
>Earth symbols at l | | |