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Neutral-ground bonding for wall receptacles
|
|
| Amos Kariuki 2008-01-07, 8:25 pm |
| Have a bonding question,
For old houses that may be missing an available grounding wire (from
the distribution panel) at the wall receptacle, the NEC forbids
bonding the ground terminal of a three plug receptacle to the neutral--
for purposes of providing a ground fault current path. What is the
reason that this is forbidden and what is the specific hazard posed?
The main reason one would want to do this is to provide a three plug
wall receptacle having an available ground terminal--for old houses
that may not have an available ground fault path. I'm aware that you
can use a three plug GFCI with the ground terminal floating but I'm
curious as to what hazard is posed by the neutral-ground bonding.
Amos Kariuki
| |
| Dave22 2008-01-07, 8:25 pm |
| On Jan 7, 3:49 pm, Amos Kariuki <amoskah...@gmail.com> wrote:
> Have a bonding question,
for many appliances and devices the grounding pin is connected to the
equipment chassis that could be touched by someone.
If the grounding pin in the outlet is connected directly to the
neutral conductor an overload from another component plugged into the
same circuit could cause a dangerous voltage to appear on that
grounding pin due to the voltage drop from the current in the neutral.
Since a true grounding conductor does not carry anything but fault
currents this condition is less likly to occur with correct wiring.
Dave 22
>
> For old houses that may be missing an available grounding wire (from
> the distribution panel) at the wall receptacle, the NEC forbids
> bonding the ground terminal of a three plug receptacle to the neutral--
> for purposes of providing a ground fault current path. What is the
> reason that this is forbidden and what is the specific hazard posed?
>
> The main reason one would want to do this is to provide a three plug
> wall receptacle having an available ground terminal--for old houses
> that may not have an available ground fault path. I'm aware that you
> can use a three plug GFCI with the ground terminal floating but I'm
> curious as to what hazard is posed by the neutral-ground bonding.
>
> Amos Kariuki
| |
| Michael A. Terrell 2008-01-07, 8:25 pm |
| Dave22 wrote:
>
> On Jan 7, 3:49 pm, Amos Kariuki <amoskah...@gmail.com> wrote:
> for many appliances and devices the grounding pin is connected to the
> equipment chassis that could be touched by someone.
>
> If the grounding pin in the outlet is connected directly to the
> neutral conductor an overload from another component plugged into the
> same circuit could cause a dangerous voltage to appear on that
> grounding pin due to the voltage drop from the current in the neutral.
>
> Since a true grounding conductor does not carry anything but fault
> currents this condition is less likly to occur with correct wiring.
If the two are bonded at the outlet and the neutral opens, the case
can be at full line potential.
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
| |
|
| On Mon, 7 Jan 2008 16:11:09 -0800 (PST), Dave22
<dsquier1@earthlink.net> wrote:
[color=darkred]
>On Jan 7, 3:49 pm, Amos Kariuki <amoskah...@gmail.com> wrote:
>for many appliances and devices the grounding pin is connected to the
>equipment chassis that could be touched by someone.
>
>If the grounding pin in the outlet is connected directly to the
>neutral conductor an overload from another component plugged into the
>same circuit could cause a dangerous voltage to appear on that
>grounding pin due to the voltage drop from the current in the neutral.
>
>Since a true grounding conductor does not carry anything but fault
>currents this condition is less likly to occur with correct wiring.
>
>Dave 22
>
Another way to look at the problem is to see that without the
grounding conductor, a "ground fault" would allow return current to
flow through the ground, pipes, etc., all of which would be in
parallel with the neutral.
With the grounding conductor, fault current sees a low impedance path
back to the service ground.
An important consideration is that ground fault currents may be tens
of amperes but be insufficient to trip protective devices and clear
the fault, even for long periods of time. Meanwhile, a portion of that
current would be travelling through the ground (earth, pipes, etc.) in
parallel with the neutral.
Chuck
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| |
| Amos Kariuki 2008-01-07, 8:25 pm |
| On Jan 7, 6:11 pm, Dave22 <dsqui...@earthlink.net> wrote:
> On Jan 7, 3:49 pm, Amos Kariuki <amoskah...@gmail.com> wrote:> Have a bonding question,
>
> If the grounding pin in the outlet is connected directly to the
> neutral conductor an overload from another component plugged into the
> same circuit could cause a dangerous voltage to appear on that
> grounding pin due to the voltage drop from the current in the neutral.
>
Doesn't the same argument apply whether the neutral-ground bonding is
done at the wall receptacle or at the distribution panel, i.e. a
voltage drop in the neutral will be seen at the ground terminal for
both cases?
| |
| Amos Kariuki 2008-01-07, 8:25 pm |
| On Jan 7, 6:32 pm, "Michael A. Terrell" <mike.terr...@earthlink.net>
wrote:
> If the two are bonded at the outlet and the neutral opens, the case
> can be at full line potential.
Agreed.
I was assuming that failure of the neutral inside the building wiring
would be an unlikely event. In a similar case, it seems strange that
neutral-ground bonding at the service distribution panel is allowed by
the NEC, since the neutral conductor connection could fail at the
(outside) transformer.
For this case, it seems like it would be safer to always require a
separate ground wire, that is bonded only at the transformer.
Amos Kariuki
| |
|
| Amos Kariuki wrote:
> Have a bonding question,
>
> For old houses that may be missing an available grounding wire (from
> the distribution panel) at the wall receptacle, the NEC forbids
> bonding the ground terminal of a three plug receptacle to the neutral--
> for purposes of providing a ground fault current path. What is the
> reason that this is forbidden and what is the specific hazard posed?
>
> The main reason one would want to do this is to provide a three plug
> wall receptacle having an available ground terminal--for old houses
> that may not have an available ground fault path. I'm aware that you
> can use a three plug GFCI with the ground terminal floating but I'm
> curious as to what hazard is posed by the neutral-ground bonding.
>
> Amos Kariuki
If wired correctly, the neutral, which is a current
carrying conductor, cannot come in contact with a human
under normal circumstances. The ground, which is
_not_ a current carrying conductor, is regularly
in contact with humans at many metal case appliances
and tools.
It is obvoius that you do *not* want a human to come
into contact with a current carrying conductor. You
want to keep the current away from the human. Here's
a "picture" of what can happen.
-------
Hot------------------|Recept |---Appliance---+
| | |
Neutral--- Defect ---|Nuetral|---+-----------+
| | | | <Illegal
| |Ground |---+ Connection
| ------- |
| |
Ground-------You-----------------+
Because of the illegal connection, a defect in the
neutral can expose you to danger. Current could flow
through the appliance, the illegal connection and you
back to ground. If the illegal connection was not there,
the defect in the neutral would not expose you to the
danger illustrated.
Ed
| |
| gfretwell@aol.com 2008-01-08, 3:25 am |
| On Mon, 7 Jan 2008 15:49:21 -0800 (PST), Amos Kariuki
<amoskahiga@gmail.com> wrote:
>Have a bonding question,
>
>For old houses that may be missing an available grounding wire (from
>the distribution panel) at the wall receptacle, the NEC forbids
>bonding the ground terminal of a three plug receptacle to the neutral--
>for purposes of providing a ground fault current path. What is the
>reason that this is forbidden and what is the specific hazard posed?
>
>The main reason one would want to do this is to provide a three plug
>wall receptacle having an available ground terminal--for old houses
>that may not have an available ground fault path. I'm aware that you
>can use a three plug GFCI with the ground terminal floating but I'm
>curious as to what hazard is posed by the neutral-ground bonding.
>
>Amos Kariuki
How do you know the white wire is really grounded? Somebody night have
swapped them on an upstream receptacle. Then what do you think you
would have?
| |
| Gerald Newton 2008-01-08, 9:25 am |
| On Jan 7, 2:49=A0pm, Amos Kariuki <amoskah...@gmail.com> wrote:
> Have a bonding question,
>
> For old houses that may be missing an available grounding wire (from
> the distribution panel) at the wall receptacle, the NEC forbids
> bonding the ground terminal of a three plug receptacle to the neutral--
> for purposes of providing a ground fault current path. =A0What is the
> reason that this is forbidden and what is the specific hazard posed?
>
> The main reason one would want to do this is to provide a three plug
> wall receptacle having an available ground terminal--for old houses
> that may not have an available ground fault path. =A0I'm aware that you
> can use a three plug GFCI with the ground terminal floating but I'm
> curious as to what hazard is posed by the neutral-ground bonding.
>
> Amos Kariuki
We grounded ranges, cooktops, ovens, and laundry dryers for about 60
years using the neutral. They claim this practice was adopted during
WWII to save on copper.
Today in many older homes this practice remains in place. Although
the NEC forbids this practice for 120 volt 15 and 20 ampere
receptacles, I think it might be an acceptacle practice as it has
proven to be safe for the ranges and dryers for many years.
| |
|
| On Tue, 08 Jan 2008 01:17:34 -0500, gfretwell@aol.com wrote:
>On Mon, 7 Jan 2008 15:49:21 -0800 (PST), Amos Kariuki
><amoskahiga@gmail.com> wrote:
>
>
>
>How do you know the white wire is really grounded? Somebody night have
>swapped them on an upstream receptacle. Then what do you think you
>would have?
How do you know the green wire is really grounded?
Chuck
----== Posted via droptable.com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.droptable.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----
| |
| phil-news-nospam@ipal.net 2008-01-08, 1:25 pm |
| On Mon, 7 Jan 2008 17:12:31 -0800 (PST) Amos Kariuki <amoskahiga@gmail.com> wrote:
| On Jan 7, 6:32 pm, "Michael A. Terrell" <mike.terr...@earthlink.net>
| wrote:
|> If the two are bonded at the outlet and the neutral opens, the case
|> can be at full line potential.
|
| Agreed.
|
| I was assuming that failure of the neutral inside the building wiring
| would be an unlikely event. In a similar case, it seems strange that
| neutral-ground bonding at the service distribution panel is allowed by
| the NEC, since the neutral conductor connection could fail at the
| (outside) transformer.
While it might be an unlikely event, when it might happen it can be a
very serious event ... killing people.
And in the more common scenarios, problems can happen with the voltage
drop of the neutral being applied to the appliance case.
| For this case, it seems like it would be safer to always require a
| separate ground wire, that is bonded only at the transformer.
Or at least at a common point at the entrance where it is also earthed,
which is exactly what the NEC requires.
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
| gfretwell@aol.com 2008-01-08, 1:25 pm |
| On Tue, 08 Jan 2008 08:51:15 -0500, Chuck <nospam@nospam.at.all>
wrote:
>
>How do you know the green wire is really grounded?
>
>Chuck
It is very common to find white and black swapped in receptacles.
| |
|
| Gerald Newton wrote:
> On Jan 7, 2:49 pm, Amos Kariuki <amoskah...@gmail.com> wrote:
>
> We grounded ranges, cooktops, ovens, and laundry dryers for about 60
> years using the neutral. They claim this practice was adopted during
> WWII to save on copper.
> Today in many older homes this practice remains in place. Although
> the NEC forbids this practice for 120 volt 15 and 20 ampere
> receptacles, I think it might be an acceptacle practice as it has
> proven to be safe for the ranges and dryers for many years.
Range and drier circuits had to originate in the service panel and IIRC
had to be connected with service entrance cable.
If you are talking about 15/20A circuits, there can be many splices back
to the panel where the neutral can open or black and white be swapped.
If wired correctly now, the black and white can be swapped when a
receptacle is replaced.
--
bud--
| |
| Gerald Newton 2008-01-08, 5:25 pm |
| On Jan 8, 8:20=A0am, bud-- <remove.budn...@isp.com> wrote:
> Gerald Newton wrote:
>
[color=darkred]
>
[color=darkred]
>
>
>
> Range and drier circuits had to originate in the service panel and IIRC
> had to be connected with service entrance cable.
>
> If you are talking about 15/20A circuits, there can be many splices back
> to the panel where the neutral can open or black and white be swapped.
> If wired correctly now, the black and white can be swapped when a
> receptacle is replaced.
>
> --
> bud--- Hide quoted text -
>
> - Show quoted text -
I beg your pardon; "originate at the service" for dryer and range
circuits was not a NEC requirement for many years. I wired many four
plexes where the circuits originated at the subpanel and that was to
code.
I also read that in some European countries they use the neutral for
grounding. To me it makes more sense to use the neutral for grounding
since if you lose it the circuit stops working. There is no way of
knowing if you lose the grounding conductor or not unless you test for
it.
| |
| Amos Kariuki 2008-01-08, 8:25 pm |
| On Jan 8, 9:27 am, phil-news-nos...@ipal.net wrote:
> | For this case, it seems like it would be safer to always require a
> | separate ground wire, that is bonded only at the transformer.
>
> Or at least at a common point at the entrance where it is also earthed,
> which is exactly what the NEC requires.
If the neutral fails at the transformer, you'd still have the same
safety hazard since the earth bonding at the service entrance doesn't
provide you any significant safeguards against electrocution (for this
case). Furthermore, it's likely that you'd also have a brownout
condition (equipment hazard) since the ground resistance would now be
in series with your building load (from the utility transformer's
perspective).
| |
| Michael A. Terrell 2008-01-08, 8:25 pm |
| Amos Kariuki wrote:
>
> On Jan 8, 9:27 am, phil-news-nos...@ipal.net wrote:
>
> If the neutral fails at the transformer, you'd still have the same
> safety hazard since the earth bonding at the service entrance doesn't
> provide you any significant safeguards against electrocution (for this
> case). Furthermore, it's likely that you'd also have a brownout
> condition (equipment hazard) since the ground resistance would now be
> in series with your building load (from the utility transformer's
> perspective).
In the US, a seperate ground is used at the main disconnect.
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
| |
| Michael A. Terrell 2008-01-08, 8:25 pm |
| Amos Kariuki wrote:
>
> On Jan 7, 6:32 pm, "Michael A. Terrell" <mike.terr...@earthlink.net>
> wrote:
>
> Agreed.
>
> I was assuming that failure of the neutral inside the building wiring
> would be an unlikely event. In a similar case, it seems strange that
> neutral-ground bonding at the service distribution panel is allowed by
> the NEC, since the neutral conductor connection could fail at the
> (outside) transformer.
It might be an 'unlikely event' to develop an open neutral, but I've
seen more than a few in the last 40+ years.
> For this case, it seems like it would be safer to always require a
> separate ground wire, that is bonded only at the transformer.
>
> Amos Kariuki
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
| |
| Michael A. Terrell 2008-01-08, 8:25 pm |
| gfretwell@aol.com wrote:
>
> On Tue, 08 Jan 2008 08:51:15 -0500, Chuck <nospam@nospam.at.all>
> wrote:
>
>
> It is very common to find white and black swapped in receptacles.
I've run into several places where the wire is spliced to another
color, and pulled through conduit. One was pink at on end, and yellow
at the other end.  It was between floor outlets in a school office,
and the janitor had removed the screw in covers before using a floor
scrubber. Then he put them back, without the rubber seals. The conduit
was full of dirty water and floor wax. The power for the school's
intercom system ran through the same conduit, and it had opened, due to
electrolysis. I though I was going to need a blasting cap and new
conduit, but after a couple hours of work, I managed to open the conduit
enough to run new wire. Needless to say, it was an expensive repair,
and they fired that janitor, before they found other stupid things that
he'd done.
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
| |
| Beachcomber 2008-01-08, 8:25 pm |
|
>I beg your pardon; "originate at the service" for dryer and range
>circuits was not a NEC requirement for many years. I wired many four
>plexes where the circuits originated at the subpanel and that was to
>code.
>I also read that in some European countries they use the neutral for
>grounding. To me it makes more sense to use the neutral for grounding
>since if you lose it the circuit stops working. There is no way of
>knowing if you lose the grounding conductor or not unless you test for
>it.
A lot of code rulings are partially based on probability. The
probability of a ground/neutral connection opening up on a range or
dryer (assuming it was installed correctly in the first place) is
very, very low. These conductors are typically larger than other
wiring and make a home run to the disconnect panel with few or no
splices. This is why the neutral was also allowed to function as a
ground for so many years.
Even though a very small (probably insignificant) number of
"engergized dryer or range frame" accidents have been reported over
the years, it is safer still to isolate the frame with a separate
ground and keep the neutral separate, as well.
There is an added cost for doing this (running an extra wire to the
junction box - using a four conductor instead of a three conductor
hookup cord and plug, but apparently the authorities in charge think
that it is worth it.
The new 2008 code is going to require arc-fault protectors in many new
home spaces (instead of just bedrooms). Once again... this will be
at added cost to electricians, new homebuilders, and new home
purchasers. Once again, the code authorities believe that this will
prevent a few fires from happening that might otherwise burn down your
house.
Beachcomber
| |
| phil-news-nospam@ipal.net 2008-01-08, 9:25 pm |
| On Mon, 7 Jan 2008 17:05:38 -0800 (PST) Amos Kariuki <amoskahiga@gmail.com> wrote:
| On Jan 7, 6:11 pm, Dave22 <dsqui...@earthlink.net> wrote:
|> On Jan 7, 3:49 pm, Amos Kariuki <amoskah...@gmail.com> wrote:> Have a bonding question,
|>
|> If the grounding pin in the outlet is connected directly to the
|> neutral conductor an overload from another component plugged into the
|> same circuit could cause a dangerous voltage to appear on that
|> grounding pin due to the voltage drop from the current in the neutral.
|>
|
| Doesn't the same argument apply whether the neutral-ground bonding is
| done at the wall receptacle or at the distribution panel, i.e. a
| voltage drop in the neutral will be seen at the ground terminal for
| both cases?
If the bonding is at the entrance panel, and earthed there, then any neutral
voltages will be held near ground potential by the low impedance path to
ground at that panel. No current will flow over any of the grounding wires
with the exception of one where a ground fault might happen. In the case
of bonding at the receptacle with no grounding wire, and no earthing, you
get the neutral voltage on the case of the appliance through its grounded
case.
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
| gfretwell@aol.com 2008-01-09, 3:25 am |
| On Tue, 8 Jan 2008 12:15:09 -0800 (PST), Gerald Newton
<electrician@electrician2.com> wrote:
>
>I beg your pardon; "originate at the service" for dryer and range
>circuits was not a NEC requirement for many years
I am not sure when/if it changed but the 75 says it has to originate
at the service. (The oldest book I have handy)
| |
| phil-news-nospam@ipal.net 2008-01-09, 3:25 am |
| On Tue, 08 Jan 2008 20:13:55 -0500 Michael A. Terrell <mike.terrell@earthlink.net> wrote:
| Amos Kariuki wrote:
|>
|> On Jan 7, 6:32 pm, "Michael A. Terrell" <mike.terr...@earthlink.net>
|> wrote:
|> > If the two are bonded at the outlet and the neutral opens, the case
|> > can be at full line potential.
|>
|> Agreed.
|>
|> I was assuming that failure of the neutral inside the building wiring
|> would be an unlikely event. In a similar case, it seems strange that
|> neutral-ground bonding at the service distribution panel is allowed by
|> the NEC, since the neutral conductor connection could fail at the
|> (outside) transformer.
|
|
| It might be an 'unlikely event' to develop an open neutral, but I've
| seen more than a few in the last 40+ years.
In about as many years I have seen 3 of these without being an electrician
one might be called to investigate. The first was in my own home when I
was in junior high. My mother was quizzing me on why some of the lights
would get dimmer while others would get brighter when she turned on the
stove elements and adjusted their heat level. I immediately knew what the
problem was, but didn't have the worse to explain it other than to say the
wiring was bad. My parents at first were not willing to accept that since
the lights were all on. I eventually convinced them the electrician needed
to be called right now. Given there had been a couple other issues with
the electrical wiring in the house before (one we rented), they finally
agreed to do so. He found the loose neutral in the panel, as well as some
exposed wiring for the stove itself. The 2nd incident with a neighbor down
the street. Her stove was smoking, especially in and around the clock it
contained (so it was using 120 volts and getting toasty from well above
that). Some arcing happened behind it. The loose neutral turned out to
be in the socket. The stove was replaced due to damage. The 3rd incident
was a loose neutral in a large room of cubicles. And this was three phase.
Maybe it was a burned out neutral due to harmonics from so many computers?
There were an average of about 2 per person (I had 4). There were about
60 programmers in the room. Lights and computers were acting funny and
things changed as people turned stuff off. Shortly, with someone else's
help who knew where it was, we got to the breaker panel. After we did
some pondering about where the cubicles were wired in, since it did not
identify things specific enough, I just grabbed the main and flipped it
off. We lost a half day of work instead of a room full of computers and
other stuff to fire.
Does this mean loose/broken neutral are rare? I certainly don't go around
hunting for them. But maybe they hunt for me?
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
| Tom Horne 2008-01-09, 3:25 am |
| Amos Kariuki wrote:
> On Jan 7, 6:11 pm, Dave22 <dsqui...@earthlink.net> wrote:
>
> Doesn't the same argument apply whether the neutral-ground bonding is
> done at the wall receptacle or at the distribution panel, i.e. a
> voltage drop in the neutral will be seen at the ground terminal for
> both cases?
Use your common sense and compare the nature of the connections at the
neutral buss, meter enclosure, demarcation point (the splices that
connect your service entry conductors to the utility's supply
conductors), with those that are made in an outlet box. The ones at and
before your Service Disconnecting Means (SDM) are tightened by the most
experienced wireman on the job, using torque measuring tools, with anti
corrosion paste applied. They are then closely inspected by the
electrical inspector and checked by the utility company's outside
wiremen prior to power being applied. Which of the two do you think is
more likely to suffer a failure? That doesn't mean that they cannot
fail because they can and do but that is a far less frequent fault then
an open neutral on a back stab receptacle in one of dozens of outlet
boxes most of which were made up by the least experienced helpers who
are being pushed for production. Just as importantly the bonding that
is done during the construction that keeps all of the conductive
surfaces at the same voltage reduces the likelihood of a fatal shock and
the malfunctioning of the served loads in the entire home provides the
impetus for the occupants to report the trouble and have it cleared. If
just one circuit is affected the occupants are more likely to try to
muddle through and the other conductive surfaces in the building are not
at the same elevated potential as the bonding pins of the faulted
circuit. The 120 volt difference between various surfaces in the home
makes a fatal shock far more likely.
--
Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison
| |
| Tom Horne 2008-01-09, 3:25 am |
| phil-news-nospam@ipal.net wrote:
> On Mon, 7 Jan 2008 17:05:38 -0800 (PST) Amos Kariuki <amoskahiga@gmail.com> wrote:
> | On Jan 7, 6:11 pm, Dave22 <dsqui...@earthlink.net> wrote:
> |> On Jan 7, 3:49 pm, Amos Kariuki <amoskah...@gmail.com> wrote:> Have a bonding question,
> |>
> |> If the grounding pin in the outlet is connected directly to the
> |> neutral conductor an overload from another component plugged into the
> |> same circuit could cause a dangerous voltage to appear on that
> |> grounding pin due to the voltage drop from the current in the neutral.
> |>
> |
> | Doesn't the same argument apply whether the neutral-ground bonding is
> | done at the wall receptacle or at the distribution panel, i.e. a
> | voltage drop in the neutral will be seen at the ground terminal for
> | both cases?
>
> If the bonding is at the entrance panel, and earthed there, then any neutral
> voltages will be held near ground potential by the low impedance path to
> ground at that panel. No current will flow over any of the grounding wires
> with the exception of one where a ground fault might happen. In the case
> of bonding at the receptacle with no grounding wire, and no earthing, you
> get the neutral voltage on the case of the appliance through its grounded
> case.
>
Phil
In most cases the impedance of the Grounding Electrode System GES is too
high to actually keep the Equipment Grounding Conductors at or close to
earth ground potential. But since all of the conductive surfaces of the
building will rise to the voltage that is being dropped across the
building's GES and the transformers Grounding Electrode in series the
voltage of the conductive surfaces in the building will be the same.
Persons coming in contact with the voltage will get a very unpleasant
shock but it is less likely to be a fatal one. IN homes on public water
systems no such voltage rise occurs because the neutral current is
distributed across all the GESs of the buildings that are served by that
transformer and across the remaining intact neutral connections if any.
Even in the unlikely event that the utility neutral is open at the
transformer their combined parallel resistance is usually low enough to
prevent any substantial rise.
One of the reasons that service equipment installed to serve
manufactured buildings post production cannot be mounted in or on the
building is that too much of such a building is likely to be both
conductive and poorly grounded making the exterior of such a structure
uniquely dangerous if an open neutral occurs in its supply conductors if
that neutral was bonded to the frame of the manufactured building. Such
services must be mounted off of the structure and a separate Equipment
Grounding Conductor must be run with the supply feeder to the structure.
This assures that there is a low likelihood of an open neutral
energizing the entire building because the utility neutral is usually
run underground to those services reducing the likelihood of physical
damage. The arrangements spelled out in the NEC for recreational
vehicles and mobile equipment are similar.
--
Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison
| |
| Tom Horne 2008-01-09, 3:25 am |
| Gerald Newton wrote:
> On Jan 7, 2:49 pm, Amos Kariuki <amoskah...@gmail.com> wrote:
>
> We grounded ranges, cook tops, ovens, and laundry dryers for about 60
> years using the neutral. They claim this practice was adopted during
> WWII to save on copper.
> Today in many older homes this practice remains in place. Although
> the NEC forbids this practice for 120 volt 15 and 20 ampere
> receptacles, I think it might be an acceptable practice as it has
> proven to be safe for the ranges and dryers for many years.
Gerald
Once again, as I opined in another answer on this question, the
difference is in the nature of the connections themselves. The circuit
must originate in the Service Equipment enclosure, the conductors are
heavier, invariably multi stranded, and the connections are made using
single conductor terminals designed for the purpose. The rate of
failures was perceived to be low enough to be acceptable. It was
actually the advent of better data collection and analysis that was the
three wire 120/240 volt circuits undoing. The NEC code making panel
became aware that failures were far more common then was believed
previously.
--
Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison
| |
| phil-news-nospam@ipal.net 2008-01-09, 3:25 am |
| On Tue, 08 Jan 2008 11:54:32 -0500 gfretwell@aol.com wrote:
| On Tue, 08 Jan 2008 08:51:15 -0500, Chuck <nospam@nospam.at.all>
| wrote:
|
|>>How do you know the white wire is really grounded? Somebody night have
|>>swapped them on an upstream receptacle. Then what do you think you
|>>would have?
|>
|>How do you know the green wire is really grounded?
|>
|>Chuck
|
|
| It is very common to find white and black swapped in receptacles.
And no one, trying combinations to see what works, would ever hook up a
receptacle between black and green?
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
| phil-news-nospam@ipal.net 2008-01-09, 3:25 am |
| On Tue, 8 Jan 2008 02:04:21 -0800 (PST) Gerald Newton <electrician@electrician2.com> wrote:
| We grounded ranges, cooktops, ovens, and laundry dryers for about 60
| years using the neutral. They claim this practice was adopted during
| WWII to save on copper.
You mean there was a separate grounding wire before WWII?
| Today in many older homes this practice remains in place. Although
| the NEC forbids this practice for 120 volt 15 and 20 ampere
| receptacles, I think it might be an acceptacle practice as it has
| proven to be safe for the ranges and dryers for many years.
They should be quite safe with a neutral in place of ground when:
1. All the loads in the appliance are wired L-L, e.g. 240 volts
2. The appliance is on its own dedicated circuit
3. The circuit is sourced from the main panel that has the N-G bond
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
| Beachcomber 2008-01-09, 3:25 am |
|
>
>| Today in many older homes this practice remains in place. Although
>| the NEC forbids this practice for 120 volt 15 and 20 ampere
>| receptacles, I think it might be an acceptacle practice as it has
>| proven to be safe for the ranges and dryers for many years.
>
>They should be quite safe with a neutral in place of ground when:
>
>1. All the loads in the appliance are wired L-L, e.g. 240 volts
>2. The appliance is on its own dedicated circuit
>3. The circuit is sourced from the main panel that has the N-G bond
>
>--
Most dryers in the US have 120V motors, and lamps. Many ranges also
have 120 V. oven lights, and clocks, and sometimes blowers and, as I
remember from my childhood, often there was a two prong convenience
outlets mounted near the clock.
..... This means that there will be at least some neutral current. So
maybe it isn't so safe if the neutral is connected to the frame?
Phil had a good question. Assuming that they had 220V appliances
before WWII, did they actually run a separate conductor to ground
these things? (and a neutral?)
A related interesting side note from Wikepedia:
Philip F. Labre invents the grounded outlet in Milwaukee (1928)
http://en.wikipedia.org/wiki/Domest...#Earth.2FGround
| |
|
| Gerald Newton wrote:
> On Jan 8, 8:20 am, bud-- <remove.budn...@isp.com> wrote:
>
> I beg your pardon; "originate at the service" for dryer and range
> circuits was not a NEC requirement for many years. I wired many four
> plexes where the circuits originated at the subpanel and that was to
> code.
For the code I just looked at the requirement was
- insulated ground wire
or
- service entrance cable originating in the service panel.
That eliminates Romex unless it has an insulated ground wire but some
methods could use a subpanel.
--
bud--
| |
| gfretwell@aol.com 2008-01-09, 5:25 pm |
| On Wed, 09 Jan 2008 09:13:23 -0600, bud-- <remove.budnews@isp.com>
wrote:
>For the code I just looked at the requirement was
>- insulated ground wire
>or
>- service entrance cable originating in the service panel.
When they do use Romex you will typically see the bare ground wire
going to the box or backstrap of a surface mount receptacle. The
insulated white wire goes to the center pin of a 3 terminal
receptacle.
That is why I always have people look before they assume they can't
convert to 4 pin receptacles.
| |
| Gerald Newton 2008-01-09, 5:25 pm |
| On Jan 8, 7:47=A0pm, Tom Horne <horn...@veriqrmzon.net> wrote:
> Gerald Newton wrote:
>
[color=darkred]
>
[color=darkred]
>
>
>
> Gerald
> Once again, as I opined in another answer on this question, the
> difference is in the nature of the connections themselves. =A0The circuit
> must originate in the Service Equipment enclosure, the conductors are
> heavier, invariably multi stranded, and the connections are made using
> single conductor terminals designed for the purpose. =A0The rate of
> failures was perceived to be low enough to be acceptable. =A0It was
> actually the advent of better data collection and analysis that was the
> three wire 120/240 volt circuits undoing. =A0The NEC code making panel
> became aware that failures were far more common then was believed
> previously.
> --
> Tom Horne
>
> "This alternating current stuff is just a fad. =A0It is much too dangerous=
> for general use." =A0Thomas Alva Edison- Hide quoted text -
>
> - Show quoted text -
As I recall from reading the original Soares book on grounding where
he devoted a whole chapter on the history of grounding, at one time in
the early 1900's there was an international debate on whether grounded
systems were better than ungrounded systems. As I recall at one time
all the grounding was removed from the services in New York City
because they thought ungrounded systems were the way to go.
Eventually they decided that grounded systems provided superior
protection for humans while ungrounded systems were better for not
acting as a source of ignition for fires. But I still maintain that
if the ranges and dryers could be grounded using a neutral for 60
years that this is a viable alternative that could work throughout the
electrical system. Just because the code says it can't be done does
not necessarily mean it is not a safe option. I for one am convinced
there is a great deal of lobbying by the copper industry to use more
copper in our electrical systems and that not all options are given
equal opportunity when decisions are made.
| |
|
| On Wed, 9 Jan 2008 12:49:00 -0800 (PST), Gerald Newton
<electrician@electrician2.com> wrote:
>
>As I recall from reading the original Soares book on grounding where
>he devoted a whole chapter on the history of grounding, at one time in
>the early 1900's there was an international debate on whether grounded
>systems were better than ungrounded systems. As I recall at one time
>all the grounding was removed from the services in New York City
>because they thought ungrounded systems were the way to go.
>Eventually they decided that grounded systems provided superior
>protection for humans while ungrounded systems were better for not
>acting as a source of ignition for fires. But I still maintain that
>if the ranges and dryers could be grounded using a neutral for 60
>years that this is a viable alternative that could work throughout the
>electrical system. Just because the code says it can't be done does
>not necessarily mean it is not a safe option. I for one am convinced
>there is a great deal of lobbying by the copper industry to use more
>copper in our electrical systems and that not all options are given
>equal opportunity when decisions are made.
A bit of a red herring.
Appliance cases grounded through the neutral were definitely safer
than those not grounded at all. That's why it was done. The question
you need to address is whether grounding through the grounding wire is
more or less safe than through the neutral.
The US Navy uses no grounded conductors at all on its ships, which is
really not intended as a safety measure, but rather to prevent
disruption of critical functions in the event of a (first) line to
ground fault. Also to avoid currents flowing in the hull, esp. through
welded joints.
Even with no grounded conductors, lethal voltages can and do arise
between ungrounded conductors and the hull due to the capacitance
effects of miles of wiring.
Ungrounded 3 phase delta systems are often found in industrial
installatiions and in many cases permitted by the code.
Chuck
----== Posted via droptable.com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.droptable.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----
| |
|
| In article <47841F71.FDE8D34A@earthlink.net>,
alt.engineering.electrical, mike.terrell@earthlink.net says...
> Amos Kariuki wrote:
>
>
> In the US, a seperate ground is used at the main disconnect.
Define "main disconnect". My last house had the entrance panel
located about 30' from the meter. There was a disconnect switch at
the meter (and of course the main breaker in the panel). I thought
the separate ground was connected back to the grounding point
(usually the entrance panel).
--
Keith
| |
|
| In article <fm1mtf0dfg@news1.newsguy.com>,
alt.engineering.electrical, phil-news-nospam@ipal.net says...
> On Tue, 08 Jan 2008 11:54:32 -0500 gfretwell@aol.com wrote:
> | On Tue, 08 Jan 2008 08:51:15 -0500, Chuck <nospam@nospam.at.all>
> | wrote:
> |
> |>>How do you know the white wire is really grounded? Somebody night have
> |>>swapped them on an upstream receptacle. Then what do you think you
> |>>would have?
> |>
> |>How do you know the green wire is really grounded?
> |>
> |>Chuck
> |
> |
> | It is very common to find white and black swapped in receptacles.
>
> And no one, trying combinations to see what works, would ever hook up a
> receptacle between black and green?
Not nearly as likely, I suspect. The "green" terminal on most
fixtures is, well, green. Many people don't know there is a
difference between the other two or that outlets are polarized. At
one time there wasn't and they weren't.
--
Keith
| |
| Tom Horne 2008-01-09, 9:25 pm |
| krw wrote:
> In article <47841F71.FDE8D34A@earthlink.net>,
> alt.engineering.electrical, mike.terrell@earthlink.net says...
>
> Define "main disconnect". My last house had the entrance panel
> located about 30' from the meter. There was a disconnect switch at
> the meter (and of course the main breaker in the panel). I thought
> the separate ground was connected back to the grounding point
> (usually the entrance panel).
>
"Service Equipment. The necessary equipment, usually consisting of a
circuit breaker(s) or switch(es) and fuse(s) and their accessories,
connected to the load end of service conductors to a building or other
structure, or an otherwise designated area, and intended to constitute
the main control and cutoff of the supply."
IOW it is the first place that the supply to the premise wiring system
can be readily opened or disconnected.
--
Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison
| |
| Tom Horne 2008-01-09, 9:25 pm |
| phil-news-nospam@ipal.net wrote:
> On Tue, 08 Jan 2008 11:54:32 -0500 gfretwell@aol.com wrote:
> | On Tue, 08 Jan 2008 08:51:15 -0500, Chuck <nospam@nospam.at.all>
> | wrote:
> |
> |>>How do you know the white wire is really grounded? Somebody night have
> |>>swapped them on an upstream receptacle. Then what do you think you
> |>>would have?
> |>
> |>How do you know the green wire is really grounded?
> |>
> |>Chuck
> |
> |
> | It is very common to find white and black swapped in receptacles.
>
> And no one, trying combinations to see what works, would ever hook up a
> receptacle between black and green?
>
It is at least less likely because the ground screw is usually painted
with green metallic paint. It is somehow beyond some people to match
the black to the brass colored screw and the white to the silver colored
screw. Then you add in the conductors that the painters spray gun made
the same color as the room's finish, the ones that are so old that the
original color coding is gone...
--
Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison
| |
| Tom Horne 2008-01-09, 9:25 pm |
| Gerald Newton wrote:
> On Jan 8, 7:47 pm, Tom Horne <horn...@veriqrmzon.net> wrote:
>
> As I recall from reading the original Soares book on grounding where
> he devoted a whole chapter on the history of grounding, at one time in
> the early 1900's there was an international debate on whether grounded
> systems were better than ungrounded systems. As I recall at one time
> all the grounding was removed from the services in New York City
> because they thought ungrounded systems were the way to go.
> Eventually they decided that grounded systems provided superior
> protection for humans while ungrounded systems were better for not
> acting as a source of ignition for fires. But I still maintain that
> if the ranges and dryers could be grounded using a neutral for 60
> years that this is a viable alternative that could work throughout the
> electrical system. Just because the code says it can't be done does
> not necessarily mean it is not a safe option. I for one am convinced
> there is a great deal of lobbying by the copper industry to use more
> copper in our electrical systems and that not all options are given
> equal opportunity when decisions are made.
Well you're convinced so there's an end to all discussion with you on
that subject.
Now for the benefit of those who are willing to read on I'll recap.
Individual conductor terminations made to listed terminal lugs using
anti corrosion paste as necessary have a far lower rate of failure then
production receptacle installations. This is especially true were push
in spring loaded receptacle terminals are used.
If I had my way we would have a separate bonding conductor all the way
back to the utility's neutral connection at the transformer so that the
hazards of an open neutral would be reduced even further. Modern
services in Europe are equipped with service ground fault protection so
that if the neutral goes open so does the main breaker.
--
Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison
| |
| Michael A. Terrell 2008-01-10, 1:29 pm |
| krw wrote:
>
> Define "main disconnect". My last house had the entrance panel
> located about 30' from the meter. There was a disconnect switch at
> the meter (and of course the main breaker in the panel). I thought
> the separate ground was connected back to the grounding point
> (usually the entrance panel).
I consider the 'Main Disconnect' as the first breaker in any
building, intended to shut off all electrical service.
A breaker, fuse or switch at the meter location, if separate from the
building's wiring would be a 'Master Disconnect'.
By this logic I have one 'Master Disconnect' at the meter, and four
buildings with a 'Main Disconnect' on my property. At one time there
were two meters on the property. The electric company made the previous
owner remove one pole that crossed the driveway. A line was run under
the driveway, and an outdoor breaker box was installed on the stump,
because that pole had supplied power to three of the buildings. What do
you call that box? It has no main breaker, yet it feeds three
additional breaker boxes?
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
| |
|
| In article <hxfhj.11480$qV.6687@trnddc03>,
alt.engineering.electrical, hornetd@veriqrmzon.net says...
> krw wrote:
>
>
> "Service Equipment. The necessary equipment, usually consisting of a
> circuit breaker(s) or switch(es) and fuse(s) and their accessories,
> connected to the load end of service conductors to a building or other
> structure, or an otherwise designated area, and intended to constitute
> the main control and cutoff of the supply."
>
> IOW it is the first place that the supply to the premise wiring system
> can be readily opened or disconnected.
Like I said, the above doesn't seem to be true then. The service
in my previous house could be "disconnected" at the meter, some
30' (across the garage, on the front porch, with great-circle
routing) from the entrance panel.
--
Keith
| |
|
| In article <47866817.75897795@earthlink.net>,
alt.engineering.electrical, mike.terrell@earthlink.net says...
> krw wrote:
>
>
> I consider the 'Main Disconnect' as the first breaker in any
> building, intended to shut off all electrical service.
Ok, we still have the same problem. ;-)
> A breaker, fuse or switch at the meter location, if separate from the
> building's wiring would be a 'Master Disconnect'.
As opposed to the "Main Disconnect"?
> By this logic I have one 'Master Disconnect' at the meter, and four
> buildings with a 'Main Disconnect' on my property.
Sure, I would expect every building to have an "entrance panel" and
"main disconnect". I don't think it's legal to have a separate
building with only a sub-panel off the entrance, is it?
> At one time there
> were two meters on the property. The electric company made the previous
> owner remove one pole that crossed the driveway.
I'd remove the pole crossing my driveway without the power company
telling me to. ;-)
> A line was run under
> the driveway, and an outdoor breaker box was installed on the stump,
> because that pole had supplied power to three of the buildings. What do
> you call that box?
Drop box? Power drop?
> It has no main breaker, yet it feeds three
> additional breaker boxes?
Oh, it has no outlets, just a junction box? I'd call it a
"junction box". ;-)
--
Keith
| |
| Michael A. Terrell 2008-01-10, 9:25 pm |
| krw wrote:
>
> In article <47866817.75897795@earthlink.net>,
> alt.engineering.electrical, mike.terrell@earthlink.net says...
>
> Ok, we still have the same problem. ;-)
>
>
> As opposed to the "Main Disconnect"?
>
>
> Sure, I would expect every building to have an "entrance panel" and
> "main disconnect". I don't think it's legal to have a separate
> building with only a sub-panel off the entrance, is it?
>
>
> I'd remove the pole crossing my driveway without the power company
> telling me to. ;-)
>
>
> Drop box? Power drop?
>
>
> Oh, it has no outlets, just a junction box? I'd call it a
> "junction box". ;-)
Woth breakers?
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
| |
| Tom Horne 2008-01-12, 3:25 am |
| Michael A. Terrell wrote:
> krw wrote:
>
>
> I consider the 'Main Disconnect' as the first breaker in any
> building, intended to shut off all electrical service.
>
> A breaker, fuse or switch at the meter location, if separate from the
> building's wiring would be a 'Master Disconnect'.
>
A breaker of switch located at the meter is just another form of Service
Equipment. The conductors from a meter enclosure that is equipped with
Service Disconnecting Means to the panel or panels they supply are
feeders rather than Service Entry Conductors. If they serve a panel
located in the same structure then the feeder has to have a separate
Equipment Grounding Conductor (EGC) and all of the EGCs from those
panels would be kept separate from the Grounded Current Carrying
Conductors [neutrals]. All of the "neutrals" would be bonded to ground
at the Service Equipment Enclosure older installations may have three
wire feeders with the "neutrals" bonded at the Building Disconnecting
Means (BDM). If a building has six or fewer circuits then the
individual breakers mounted in a main lug only (MLO) panel may serve as
the BDM.
> By this logic I have one 'Master Disconnect' at the meter, and four
> buildings with a 'Main Disconnect' on my property. At one time there
> were two meters on the property. The electric company made the previous
> owner remove one pole that crossed the driveway. A line was run under
> the driveway, and an outdoor breaker box was installed on the stump,
> because that pole had supplied power to three of the buildings. What do
> you call that box? It has no main breaker, yet it feeds three
> additional breaker boxes?
What it is called would depend on whether or not it contains breakers,
switches, or fuse pull outs. If it has no controls it is a meter
enclosure or "meter pan". If it has controls that can shut off the
current flowing to the four buildings then it is the Service Equipment
and it contains the Service Disconnecting Means.
As a rather important aside it should also contain the only Over Current
Protective Device for the water pump for that property regardless of
whether that takes the form of a breaker, fused switch, or fused
pullout. The reason that the farm bureau and other rural property
interest prefer this is it allows cutting off the power to any building
without shutting down the pump that provides the water for first aid
fire fighting efforts.
--
Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison
| |
| phil-news-nospam@ipal.net 2008-01-12, 3:25 am |
| On Thu, 10 Jan 2008 02:46:39 GMT Tom Horne <hornetd@veriqrmzon.net> wrote:
| It is at least less likely because the ground screw is usually painted
| with green metallic paint. It is somehow beyond some people to match
| the black to the brass colored screw and the white to the silver colored
| screw. Then you add in the conductors that the painters spray gun made
| the same color as the room's finish, the ones that are so old that the
| original color coding is gone...
So I guess we need to paint the other screws for them?
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
| phil-news-nospam@ipal.net 2008-01-12, 3:25 am |
| On Wed, 09 Jan 2008 07:41:07 GMT Beachcomber <invalid@notreal.none> wrote:
|
|>
|>| Today in many older homes this practice remains in place. Although
|>| the NEC forbids this practice for 120 volt 15 and 20 ampere
|>| receptacles, I think it might be an acceptacle practice as it has
|>| proven to be safe for the ranges and dryers for many years.
|>
|>They should be quite safe with a neutral in place of ground when:
|>
|>1. All the loads in the appliance are wired L-L, e.g. 240 volts
|>2. The appliance is on its own dedicated circuit
|>3. The circuit is sourced from the main panel that has the N-G bond
|>
|>--
|
| Most dryers in the US have 120V motors, and lamps. Many ranges also
| have 120 V. oven lights, and clocks, and sometimes blowers and, as I
| remember from my childhood, often there was a two prong convenience
| outlets mounted near the clock.
|
| .... This means that there will be at least some neutral current. So
| maybe it isn't so safe if the neutral is connected to the frame?
Aside from the convenience outlet (which decades ago was treated as more
of a necessity ... my grandmother frequently used it due to not enough
outlets in the kitchen), all the rest could be redesigned for 240 volts.
The light would have to have a different kind of socket to prevent contact
with either conductor as well avoiding any wrong voltage bulb. Today, we
don't need that convenience outlet, thanks to the NEC requiring plenty of
outlets in the kitchen. I'd rather see the big appliances run on NEMA 6-30,
6-50, etc. Eliminate a wire; copper is getting expensive.
BTW, have you ever compared a NEMA 6-15P to a NEMA 14-15R :-)
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
| phil-news-nospam@ipal.net 2008-01-12, 1:25 pm |
| On Wed, 9 Jan 2008 12:49:00 -0800 (PST) Gerald Newton <electrician@electrician2.com> wrote:
| As I recall from reading the original Soares book on grounding where
| he devoted a whole chapter on the history of grounding, at one time in
| the early 1900's there was an international debate on whether grounded
| systems were better than ungrounded systems. As I recall at one time
| all the grounding was removed from the services in New York City
| because they thought ungrounded systems were the way to go.
| Eventually they decided that grounded systems provided superior
| protection for humans while ungrounded systems were better for not
| acting as a source of ignition for fires. But I still maintain that
| if the ranges and dryers could be grounded using a neutral for 60
| years that this is a viable alternative that could work throughout the
| electrical system. Just because the code says it can't be done does
| not necessarily mean it is not a safe option. I for one am convinced
| there is a great deal of lobbying by the copper industry to use more
| copper in our electrical systems and that not all options are given
| equal opportunity when decisions are made.
As long as the ciruit originates from the main panel, and assuming things
are installed right at that panel, the electrical potential on the appliance
frame should not be contributed to by other circuits any more so that would
be the case with a separate EGC. There would be more potential in the frame
due to the imbalance in the appliance itself. As long as the heavy loads,
e.g. the heating elements, are connected L-L at 240 volts (not all are),
then the imbalance is limited to little things like the light and clock and
that convenience outlet.
I personally still believe that with the EGC it is safe_R_ enough that I
wouldn't even think of doing it differently even of the NEC changed and
went back to allowing imbalanced loads and "EGC" to share the same wire.
That's not where I would want to "save copper". Although it is one of
those "impossible battles", I'd much prefer eliminating any load connected
to the neutral and not have the neutral (at least for the 240 volt loads).
We have 3-wire (with or without separate EGC) utilization devices, and thus
circuits, IMHO, strictly for legacy reasons. Today we don't need the 120
volt outlet on the stove (I've not seen one on a new one in decades). Today
we can run all the components of a stove or dryer directly on 240 volts via
a L-L connection and have the third wire strictly for EGC. Motors can be
made with dual windings that can be strapped for 120 or 240 volt operation
so they can be the same motor in a 240 volt electric dryer and a 120 volt
fossil fuel dryer. Electronics control can be operated from a switching
power supply that easily operates on the 100 to 240 volt range. Lights
can be operated from that 12 volt DC output of that electronic PSU and be
more reliable that way (thicker filaments). There is no longer any big
_economic_ need for a neutral. I would contend that it would also, in a
tiny way, contribute to saving a small amount of energy. The remaining
issue is whether such appliances would need a NEMA 14-XX plug to fit the
outlets of older homes or a NEMA 6-XX plug to fit the outlets of homes
that are wired without the neutral to these dedicated receptacles. It
would have to be a choice made at purchase for self-installed or by the
installer if installed by the tech.
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
| phil-news-nospam@ipal.net 2008-01-12, 1:25 pm |
| On Wed, 09 Jan 2008 16:18:55 -0500 Chuck <nospam@nospam.at.all> wrote:
| Ungrounded 3 phase delta systems are often found in industrial
| installatiions and in many cases permitted by the code.
These are under supervision of appropriately trained personnel who are
supposed to be able to handle the exceptional conditions. They are
"relatively" safe because most of the time they are just as safe as
grounded systems. The times they are not would not get ignored since
there would be alarms in the right places alerting the right people.
You wouldn't have one of these in your home (even if you could get
three phase power there at any voltage and configuration you wanted
and had stuff that would be happy to use it).
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
| phil-news-nospam@ipal.net 2008-01-12, 1:25 pm |
| On Thu, 10 Jan 2008 03:02:11 GMT Tom Horne <hornetd@veriqrmzon.net> wrote:
| If I had my way we would have a separate bonding conductor all the way
| back to the utility's neutral connection at the transformer so that the
| hazards of an open neutral would be reduced even further. Modern
| services in Europe are equipped with service ground fault protection so
| that if the neutral goes open so does the main breaker.
Where would you bond the neutral to ground with a "bonding conductor"
(I don't know if you mean "grounding conductor" by that term)? I see
three or four possible scenarios:
1. What we have now, which is that the neutral is earthed at the entrance
as well as at the transformer by the utility.
2. The neutral is earthed at the entrance only.
3. The neutral is earthed at the transformer only.
4. The neutral is not earthed.
I'll rule out #4 immediately with no discussion.
I would not accept #3 at all. That puts the inspection and maintenance of
a critical element of the electrical system outside my scope of control.
If it came to this, I'd get a big dry-type transformer and derive my own
120/240 system out of the 240 L-L coming in and earth my own neutral.
FYI, I have seen several cases of broken ground wires on utility poles.
Since those were not getting maintained, and what I could see was only a
subset of possible places they could fail, I would not want to ever depend
on the utility to get things right.
So #2 is essentially equivalent to what exists in many places already.
I'll stick with having my own grounding electrodes, whatever the utility
does.
| "This alternating current stuff is just a fad. It is much too dangerous
| for general use." Thomas Alva Edison
Mr. Edison was a patent monger who didn't like that Mr. Westinghouse had a
bunch of them for AC. His electrical system sucked. His light bulb filament
sucked. His phonograph sucked. I can't think of anything he invented that
didn't need some major improvements before they become practically usable.
He did just enough to get enough of a patent to be sure he got money even if
someone else fixed his ideas. I'd bet that if he had never been around, most
of the things he "invented" would have been invented, anyway, by the time
they were actually used on a wide scale, according to our history.
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
|
| On 12 Jan 2008 17:09:20 GMT, phil-news-nospam@ipal.net wrote:
>On Wed, 09 Jan 2008 16:18:55 -0500 Chuck <nospam@nospam.at.all> wrote:
>
>| Ungrounded 3 phase delta systems are often found in industrial
>| installatiions and in many cases permitted by the code.
>
>These are under supervision of appropriately trained personnel who are
>supposed to be able to handle the exceptional conditions. They are
>"relatively" safe because most of the time they are just as safe as
>grounded systems. The times they are not would not get ignored since
>there would be alarms in the right places alerting the right people.
>You wouldn't have one of these in your home (even if you could get
>three phase power there at any voltage and configuration you wanted
>and had stuff that would be happy to use it).
Hello Phil,
I think an argument could even be made that 3 phase ungrounded systems
are always at least as safe as grounded systems in the following
sense.
Considering the line-to-ground capacitance, there is always some line
to ground voltage, but it could be less lethal than the line-to-ground
voltage of a grounded neutral system. Difficult to generalize, but
even more difficult to imagine a grounded neutral system being less
lethal at the same system voltage levels.
In the event of a line-to-ground short, the line-to-ground voltage of
an ungrounded system would be no higher than with a grounded neutral
system.
The ground fault indicators you mention are used to indicate a fault
while allowing essential systems to continue functioning until it is
economical or safe to undertake repairs. When a second ground fault
occurs, it will clear both faults. While a ground fault indication
suggests reduced safety levels for personnel coming into contact with
an ungrounded line, this is a questionable function since voltage
levels may have been lethal even prior to the ground fault. The
trained supervisors have other objectives in their sights.
None of this is intended to question the wisdom of NEC grounding
requirements for grounded systems.
Chuck
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| |
| phil-news-nospam@ipal.net 2008-01-12, 1:25 pm |
| On Sat, 12 Jan 2008 12:38:11 -0500 Chuck <nospam@nospam.at.all> wrote:
| On 12 Jan 2008 17:09:20 GMT, phil-news-nospam@ipal.net wrote:
|
|>On Wed, 09 Jan 2008 16:18:55 -0500 Chuck <nospam@nospam.at.all> wrote:
|>
|>| Ungrounded 3 phase delta systems are often found in industrial
|>| installatiions and in many cases permitted by the code.
|>
|>These are under supervision of appropriately trained personnel who are
|>supposed to be able to handle the exceptional conditions. They are
|>"relatively" safe because most of the time they are just as safe as
|>grounded systems. The times they are not would not get ignored since
|>there would be alarms in the right places alerting the right people.
|>You wouldn't have one of these in your home (even if you could get
|>three phase power there at any voltage and configuration you wanted
|>and had stuff that would be happy to use it).
|
| Hello Phil,
|
| I think an argument could even be made that 3 phase ungrounded systems
| are always at least as safe as grounded systems in the following
| sense.
|
| Considering the line-to-ground capacitance, there is always some line
| to ground voltage, but it could be less lethal than the line-to-ground
| voltage of a grounded neutral system. Difficult to generalize, but
| even more difficult to imagine a grounded neutral system being less
| lethal at the same system voltage levels.
In the absence of a line-to-ground short, I don't see a significant
issue with an ungrounded system.
| In the event of a line-to-ground short, the line-to-ground voltage of
| an ungrounded system would be no higher than with a grounded neutral
| system.
How so? The neutral would be at the mid point. If a line were grounded,
we're talking about (for example) 480 volts L-G, vs. 277 volts L-G. If
there was a L-G fault in an ungrounded system, that becomes the same as
a grounded corner delta.
| The ground fault indicators you mention are used to indicate a fault
| while allowing essential systems to continue functioning until it is
| economical or safe to undertake repairs. When a second ground fault
| occurs, it will clear both faults. While a ground fault indication
| suggests reduced safety levels for personnel coming into contact with
| an ungrounded line, this is a questionable function since voltage
| levels may have been lethal even prior to the ground fault. The
| trained supervisors have other objectives in their sights.
I don't agree that a second fault is assured to clear both faults. The
two faults may be in separate places. If at least one of them is not a
fault relative to the EGC (for example a damaged line wire on the shop
floor behind the equipment that just ran over it), you could see a low
enough current level that would not clear the fault, but could still be
a substantial fault current.
| None of this is intended to question the wisdom of NEC grounding
| requirements for grounded systems.
There are valid industrial needs for various ungrounded, or unusually
grounded, electrical systems. Those need to be handled in special ways
and in some cases electricans always on site, or at least procedures
for handling them (who to call, steps to isolate, etc).
I'm just saying, these things are not so maintenance free we could use
them in our homes.
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
|
| On 12 Jan 2008 18:05:55 GMT, phil-news-nospam@ipal.net wrote:
>snip
>| In the event of a line-to-ground short, the line-to-ground voltage of
>| an ungrounded system would be no higher than with a grounded neutral
>| system.
>
>How so? The neutral would be at the mid point. If a line were grounded,
>we're talking about (for example) 480 volts L-G, vs. 277 volts L-G. If
>there was a L-G fault in an ungrounded system, that becomes the same as
>a grounded corner delta.
>
>
I should have said that differently. Ignoring capacitance and leakage,
someone who is grounded could touch any of the hot lines without
suffering injury. Not the case with grounded systems. The full L-G
voltage at low impedance is always present.
Worst case for an ungrounded system is a L-G short which (keeping the
voltage the same) is no worse than the normal case for a grounded
system. I wanted to focus on the topology rather than specific voltage
levels.
>| The ground fault indicators you mention are used to indicate a fault
>| while allowing essential systems to continue functioning until it is
>| economical or safe to undertake repairs. When a second ground fault
>| occurs, it will clear both faults. While a ground fault indication
>| suggests reduced safety levels for personnel coming into contact with
>| an ungrounded line, this is a questionable function since voltage
>| levels may have been lethal even prior to the ground fault. The
>| trained supervisors have other objectives in their sights.
>
>I don't agree that a second fault is assured to clear both faults. The
>two faults may be in separate places. If at least one of them is not a
>fault relative to the EGC (for example a damaged line wire on the shop
>floor behind the equipment that just ran over it), you could see a low
>enough current level that would not clear the fault, but could still be
>a substantial fault current.
>
Here I was thinking of a L-G short mentioned earlier as the fault. Two
concurrent L-G shorts becomes a L-L short and obviously will trip
breakers. My mind is on naval vessels where "ground" is an extremely
low resistance steel hull. You're correct that a high resistance
ground fault might not be cleared. In a grounded system there might
be a better chance of clearing the fault given the presence of the
grounding conductor.
>
>| None of this is intended to question the wisdom of NEC grounding
>| requirements for grounded systems.
>
>There are valid industrial needs for various ungrounded, or unusually
>grounded, electrical systems. Those need to be handled in special ways
>and in some cases electricans always on site, or at least procedures
>for handling them (who to call, steps to isolate, etc).
>
>I'm just saying, these things are not so maintenance free we could use
>them in our homes.
You may be correct. The systems are certainly different. Nonetheless,
I don't think a case has been made in this thread that for residential
installations grounded systems are inherently safer than ungrounded
systems.
Chuck
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| |
|
| In article <fm9srs127h7@news4.newsguy.com>,
alt.engineering.electrical, phil-news-nospam@ipal.net says...
> On Thu, 10 Jan 2008 02:46:39 GMT Tom Horne <hornetd@veriqrmzon.net> wrote:
>
> | It is at least less likely because the ground screw is usually painted
> | with green metallic paint. It is somehow beyond some people to match
> | the black to the brass colored screw and the white to the silver colored
> | screw. Then you add in the conductors that the painters spray gun made
> | the same color as the room's finish, the ones that are so old that the
> | original color coding is gone...
>
> So I guess we need to paint the other screws for them?
It wouldn't be a bad idea. It would get the point across.
--
Keith
| |
| Ben Miller 2008-01-13, 8:25 pm |
| "Gerald Newton" <electrician@electrician2.com> wrote in message
news:3ba2d237-85c6-4e19-a169-We grounded ranges, cooktops, ovens, and
laundry dryers for about 60
years using the neutral. They claim this practice was adopted during
WWII to save on copper.
Today in many older homes this practice remains in place. Although
the NEC forbids this practice for 120 volt 15 and 20 ampere
receptacles, I think it might be an acceptacle practice as it has
proven to be safe for the ranges and dryers for many years.
That is a single appliance with no other connections on the branch circuit,
fed directly from the service panel. In the case of driers, they are often
within a few feet of the panel. That is why we have gotten away with it.
Don't extrapolate from that to the conclusion that it is a safe practice
universally
--
Benjamin D Miller, PE
www.bmillerengineering.com. As many others have pointed out, it is not.
| |
| phil-news-nospam@ipal.net 2008-01-14, 3:25 am |
| On Sun, 13 Jan 2008 19:23:26 -0600 Ben Miller <contact1@bmillerengineering.com> wrote:
| That is a single appliance with no other connections on the branch circuit,
| fed directly from the service panel. In the case of driers, they are often
| within a few feet of the panel. That is why we have gotten away with it.
| Don't extrapolate from that to the conclusion that it is a safe practice
| universally
Specifically the main service entrance panel and not a subpanel. And don't
forget that the bulk of the load is L-L leaving a relatively small neutral
current to worry about. You can't say that for other kinds of things that
someone might try to avoid a ground wire with.
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
|
|
|
|
|