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| Bill Davis Jr 2005-07-24, 9:08 pm |
| Recently moving into an old house one of my main concerns was the
electrical system.
One question I have is there a required size of cable for a 100 amp
service?
When we first moved in I was looking at the service panel. I did not
see a grounding cable to the outside. Which I know meant no grounding
rod. What scared me the most is the grounding wire that was run went
to the gas line. That for now was changed to the water line.
I would like to install the grounding rod myself but would like to
know if it matters as to what size grounding cable to run for a 100
amp service.
Thanks,
Bill
| |
|
| #6 copper for 100 amp service and two rods are required unless you have a
ground meger to test a single rod
"Bill Davis Jr" <me@home.com> wrote in message
news:on50e190o9gjf1u6neauuhout943so9a4f@4ax.com...
> Recently moving into an old house one of my main concerns was the
> electrical system.
>
> One question I have is there a required size of cable for a 100 amp
> service?
>
> When we first moved in I was looking at the service panel. I did not
> see a grounding cable to the outside. Which I know meant no grounding
> rod. What scared me the most is the grounding wire that was run went
> to the gas line. That for now was changed to the water line.
>
> I would like to install the grounding rod myself but would like to
> know if it matters as to what size grounding cable to run for a 100
> amp service.
>
> Thanks,
>
> Bill
| |
| John Hines 2005-07-24, 9:08 pm |
| Bill Davis Jr <me@home.com> wrote:
>I would like to install the grounding rod myself but would like to
>know if it matters as to what size grounding cable to run for a 100
>amp service.
#6 will work.
| |
|
|
"RBM" <rbm2(remove this)@optonline.net> wrote in
message news:DaVDe.320$mf5.64@fe12.lga...
> #6 copper for 100 amp service and two rods are
> required unless you have a ground meger to test a
> single rod
I assume you mean a rod for each phase? Why? And what
good would a "ground meger" be? I assume again the you
meant "megger"?
Just curious; I have NEVER seen more than one rod used
for any entrance on any house.
Pop
| |
|
| So I can't spell!! You are correct that only one is required but it must
have a specific ground resistance, which you need the megger to test. If you
don't have one, you must install a second rod six feet apart
"Pop" <nobody@devnull.spamcop.net> wrote in message
news:3P2dnbH7VdMt3X3fRVn-jQ@usadatanet.net...
>
> "RBM" <rbm2(remove this)@optonline.net> wrote in message
> news:DaVDe.320$mf5.64@fe12.lga...
>
> I assume you mean a rod for each phase? Why? And what good would a
> "ground meger" be? I assume again the you meant "megger"?
>
> Just curious; I have NEVER seen more than one rod used for any entrance on
> any house.
>
> Pop
>
>
| |
|
| If the house is old it probably has copper water line coming into it. This
is a better ground than ground rods so one isn't required. Also, put the
ground wire back on the gas line...it should be bonded to ground.
Fred
"Bill Davis Jr" <me@home.com> wrote in message
news:on50e190o9gjf1u6neauuhout943so9a4f@4ax.com...
> Recently moving into an old house one of my main concerns was the
> electrical system.
>
> One question I have is there a required size of cable for a 100 amp
> service?
>
> When we first moved in I was looking at the service panel. I did not
> see a grounding cable to the outside. Which I know meant no grounding
> rod. What scared me the most is the grounding wire that was run went
> to the gas line. That for now was changed to the water line.
>
> I would like to install the grounding rod myself but would like to
> know if it matters as to what size grounding cable to run for a 100
> amp service.
>
> Thanks,
>
> Bill
| |
|
| The gas line should be grounded, but not serve as the ground. Most gas
companies will insulate the inside metal gas pipe at the meter connection
from the underground metal gas pipe to reduce electrolytic caused corrosion.
"Fred" <fxallen@shawnews.ca> wrote in message
news:NgYDe.9796$s54.9149@pd7tw2no...
> If the house is old it probably has copper water line coming into it.
This
> is a better ground than ground rods so one isn't required. Also, put the
> ground wire back on the gas line...it should be bonded to ground.
>
> Fred
>
> "Bill Davis Jr" <me@home.com> wrote in message
> news:on50e190o9gjf1u6neauuhout943so9a4f@4ax.com...
>
>
| |
| PrecisionMachinisT 2005-07-24, 9:09 pm |
|
"Pop" <nobody@devnull.spamcop.net> wrote in message
news:3P2dnbH7VdMt3X3fRVn-jQ@usadatanet.net...
>
> "RBM" <rbm2(remove this)@optonline.net> wrote in
> message news:DaVDe.320$mf5.64@fe12.lga...
>
> I assume you mean a rod for each phase?
I would have to assume you are just plain ignorant when it comes to
electricity then.......
> Why? And what
> good would a "ground meger" be? I assume again the you
> meant "megger"?
>
Yes, readily apparent that's what he had meant....
Curious...got any clues as to how a megger might work ???
( this oughta be good )
> Just curious; I have NEVER seen more than one rod used
> for any entrance on any house.
>
In my area, with any new service two ground rods are required, and so far as
I know there are no exceptions allowed whatsoever.
--
SVL
| |
|
| The ground rods are required in addition to a metallic water pipe
"Fred" <fxallen@shawnews.ca> wrote in message
news:NgYDe.9796$s54.9149@pd7tw2no...
> If the house is old it probably has copper water line coming into it.
> This is a better ground than ground rods so one isn't required. Also, put
> the ground wire back on the gas line...it should be bonded to ground.
>
> Fred
>
> "Bill Davis Jr" <me@home.com> wrote in message
> news:on50e190o9gjf1u6neauuhout943so9a4f@4ax.com...
>
>
| |
| Oscar_Lives 2005-07-24, 9:09 pm |
|
"Pop" <nobody@devnull.spamcop.net> wrote in message
news:3P2dnbH7VdMt3X3fRVn-jQ@usadatanet.net...
>
> "RBM" <rbm2(remove this)@optonline.net> wrote in message
> news:DaVDe.320$mf5.64@fe12.lga...
>
> I assume you mean a rod for each phase? Why? And what good would a
> "ground meger" be? I assume again the you meant "megger"?
>
> Just curious; I have NEVER seen more than one rod used for any entrance on
> any house.
>
> Pop
Hey Poop, lighten up!
| |
|
| My 100 amp service required 2 ground rods, 8' apart on a continuous #6
conductor. But only because I do not have a metal water main going out that
could also be grounded, mine is pvc.
Ed
"Oscar_Lives" <nospam@nospam.net> wrote in message
news:bRZDe.194362$xm3.13735@attbi_s21...
>
> "Pop" <nobody@devnull.spamcop.net> wrote in message
> news:3P2dnbH7VdMt3X3fRVn-jQ@usadatanet.net...
>
>
> Hey Poop, lighten up!
>
| |
| George E. Cawthon 2005-07-24, 9:09 pm |
| Oscar_Lives wrote:
> "Pop" <nobody@devnull.spamcop.net> wrote in message
> news:3P2dnbH7VdMt3X3fRVn-jQ@usadatanet.net...
>
>
>
>
> Hey Poop, lighten up!
>
>
Why? I have a 200 amp service and a single rod.
The critical factor, at least here, is the length
of the rod and depth the rod is driven down.
And, what the hell is a ground meger? Did he mean
a ground meter? If so, what is a ground meter?
Did he mean measure the ground with an Ohm meter?
And the response is equally crazy. "A rod on
each phase" means the questioner doesn't know
anything about electricity or the correct terms.
And he things meger might be megger, but what the
heck is megger?
| |
|
| Let me splain it: NEC rules change constantly. There was a time when, if you
had a metal water pipe, it was sufficient for grounding. Next it was
required to back the water pipe up with a ground rod. If you had a well with
pvc you needed two ground rods. The latest change is that you must determine
how well connected to the earth your ground rod is, which is done using an
expensive measuring device called a megger. If you don't have one many
jurisdictions require you to add an additional rod. IMHO it makes sense. If
you drove an eight foot ground rod into dry sand it probably isn't going to
have any connection electrically with earth
"George E. Cawthon" <GeorgeC-Boise@worldnet.att.net> wrote in message
news:5w_De.21352$5N3.1069@bgtnsc05-news.ops.worldnet.att.net...
> Oscar_Lives wrote:
> Why? I have a 200 amp service and a single rod. The critical factor, at
> least here, is the length of the rod and depth the rod is driven down.
>
> And, what the hell is a ground meger? Did he mean a ground meter? If so,
> what is a ground meter? Did he mean measure the ground with an Ohm meter?
>
>
> And the response is equally crazy. "A rod on each phase" means the
> questioner doesn't know anything about electricity or the correct terms.
> And he things meger might be megger, but what the heck is megger?
| |
|
|
"RBM" <rbm2(remove this)@optonline.net> wrote in message
news:de4Ee.649$mf5.309@fe12.lga...
> Let me splain it: NEC rules change constantly. There was a time when, if
> you had a metal water pipe, it was sufficient for grounding. Next it was
> required to back the water pipe up with a ground rod. If you had a well
> with pvc you needed two ground rods. The latest change is that you must
> determine how well connected to the earth your ground rod is, which is
> done using an expensive measuring device called a megger. If you don't
> have one many jurisdictions require you to add an additional rod. IMHO it
> makes sense. If you drove an eight foot ground rod into dry sand it
> probably isn't going to have any connection electrically with earth
So having two buried in sand makes sense?
>
>
>
> "George E. Cawthon" <GeorgeC-Boise@worldnet.att.net> wrote in message
> news:5w_De.21352$5N3.1069@bgtnsc05-news.ops.worldnet.att.net...
>
>
| |
|
| "FDR" <_remove_spam_block_rzitka@hotmail.com> wrote in message
news:hP5Ee.58897$0i3.19534@twister.nyroc.rr.com...
it[color=darkred]
>
> So having two buried in sand makes sense?
FDR, did your mother have any normal children?
| |
|
|
"Milos" <dufka@ppt.invalid> wrote in message
news:4ea01$42e118c0$400474df$1028@NAXS.COM...
> "FDR" <_remove_spam_block_rzitka@hotmail.com> wrote in message
> news:hP5Ee.58897$0i3.19534@twister.nyroc.rr.com...
> it
>
> FDR, did your mother have any normal children?
>
Well, looks like your mother didn't rear any smart children.
| |
| TURTLE 2005-07-24, 9:09 pm |
|
"Bill Davis Jr" <me@home.com> wrote in message
news:on50e190o9gjf1u6neauuhout943so9a4f@4ax.com...
> Recently moving into an old house one of my main concerns was the
> electrical system.
>
> One question I have is there a required size of cable for a 100 amp
> service?
>
> When we first moved in I was looking at the service panel. I did not
> see a grounding cable to the outside. Which I know meant no grounding
> rod. What scared me the most is the grounding wire that was run went
> to the gas line. That for now was changed to the water line.
>
> I would like to install the grounding rod myself but would like to
> know if it matters as to what size grounding cable to run for a 100
> amp service.
>
> Thanks,
>
> Bill
This is Turtle.
i have a rule to go by on what size wire to use on ground rods replacements.
I get the grounding clam that will attach the wire to the clamp then to the rod.
i look at the hole of the clamp where the wire attaches to the clamp and get a
wire that will fill the hole completely. That is the size i use and sometimes
called Big Wire. It will not hurt a think over sizing this wire.
TURTLE
| |
|
| RBM is providing straight answers. This will expand on what
he had posted.
Post 1990 codes says at least one ground rod (or equivalent
and dedicated device such as earthing plate, Ufer ground, etc)
close to breaker box must be installed. This earth ground
(called a GEC in the code book), to earth AC electric, serves
multiple electrical purposes. Its human safety purpose is
defined by the National Electrical Code (NEC).
Two rods may be installed because, well, the NEC does not
even properly define what is sufficient conductive earth.
They provide a number (25 ohms) and don't even state how that
conductivity should be measured. So many electricians just
install two rods that also meet other NEC criteria such as
separation between rods. Even if two rods don't make soil
conductive enough, the code says an electrician need not do
anything more.
The water pipe was once considered a sufficient earth
ground. For numerous reasons, a water pipe is no longer
sufficient as an earth ground. But water pipe must be bonded
to breaker box to remove any electricity from those pipes.
Electricity could be from inside the building OR electricity
that could be coming from utility water pipes. The pipe must
be 'bonded' to the breaker box to remove electricity. This
water pipe bonding may also end up supplementing the earth
ground. But code no longer views water pipe as sufficient
earth ground (except in some rare cases that are irrelevant
here).
Some jurisdictions require that a gas pipe also be bonded
(not to be confused with earthing). That bonding requirement
would be uniquely defined by the local gas company. In one
example, the home had no earth ground. When a utility's
street transformer failed internally, electricity used the gas
pipe as an electrical conductor (because water pipe ground was
compromised and dedicated earth ground was never installed).
Fortunately no one was home when gas meter gaskets finally
failed and the house exploded. Just one rare example of why
proper earthing and proper bonding are important.
Absolute minimum since 1990 means a direct connection from
breaker box to cold water pipe where pipe enters building AND
a short connection from breaker box to single eight foot
ground rod. This is minimum to meet code requirements
(assuming the electrician had a meter such (as from
http://www.leminstruments.com/cgi-l....html?E+scstore
or
http://tinyurl.com/89dty ).
Numerous and very good reasons why minimal earthing is
enhanced. A number one reason - transistor safety. Earthing
defines transistor protection.
Meanwhile, volts500 in the newsgroup alt.home.repair
entitled "Grounding Rod Info" on 12 July 2003 wrote a
description of how a house should be bonded. Earthing defined
only to meet post 1990 NEC requirements; only for human
safety. Even pre-1990 homes should be upgraded to meet these
simple requirements. So simple that any homeowner can install
after a trip to Home Depot or Lowes:
http://tinyurl.com/hkjq
Bill Davis Jr wrote:
> Recently moving into an old house one of my main concerns was the
> electrical system.
>
> One question I have is there a required size of cable for a 100 amp
> service?
>
> When we first moved in I was looking at the service panel. I did
> not see a grounding cable to the outside. Which I know meant no
> grounding rod. What scared me the most is the grounding wire that
> was run went to the gas line. That for now was changed to the
> water line.
>
> I would like to install the grounding rod myself but would like to
> know if it matters as to what size grounding cable to run for a 100
> amp service.
>
> Thanks,
>
> Bill
| |
|
| RBM wrote:
> #6 copper for 100 amp service and two rods are required unless you have a
> ground meger to test a single rod
> "Bill Davis Jr" <me@home.com> wrote in message
> news:on50e190o9gjf1u6neauuhout943so9a4f@4ax.com...
>
A megger is actually used to measure very high (insulation) resistance.
To check for the required 25 ohms ground resistance you could connect
the ground rod to a hot through a lightbulb and measure the current to
the ground rod and the voltage from the ground rod to a metal burried
water pipe.
Ground rods are not noted for being a good ground which is why #6 Cu is
the wire size used to connect them. Burried metal water pipe is good.
Ground rods are a hedge for conversion of metal water service pipe to
plastic.
Bud--
| |
| George E. Cawthon 2005-07-24, 9:09 pm |
| Ok it is called a megger. Bet that is just slang
for the name--megger is probably a corruption of
the brand or megohm something. What is the real name?
RBM wrote:
> Let me splain it: NEC rules change constantly. There was a time when, if you
> had a metal water pipe, it was sufficient for grounding. Next it was
> required to back the water pipe up with a ground rod. If you had a well with
> pvc you needed two ground rods. The latest change is that you must determine
> how well connected to the earth your ground rod is, which is done using an
> expensive measuring device called a megger. If you don't have one many
> jurisdictions require you to add an additional rod. IMHO it makes sense. If
> you drove an eight foot ground rod into dry sand it probably isn't going to
> have any connection electrically with earth
>
>
>
> "George E. Cawthon" <GeorgeC-Boise@worldnet.att.net> wrote in message
> news:5w_De.21352$5N3.1069@bgtnsc05-news.ops.worldnet.att.net...
>
>
>
>
| |
|
| George E. Cawthon wrote:
[color=darkred]
> Ok it is called a megger. Bet that is just slang for the name--megger
> is probably a corruption of the brand or megohm something. What is the
> real name?
>
> RBM wrote:
>
http://www.tpub.com/doeelecsciehttp...science2172.htm
| |
|
|
|
|
"George E. Cawthon" <GeorgeC-Boise@worldnet.att.net>
wrote in message
news:qadEe.23571$5N3.9037@bgtnsc05-news.ops.worldnet.att.net...
> Ok it is called a megger. Bet that is just slang for
> the name--megger is probably a corruption of the
> brand or megohm something. What is the real name?
>
....
I think the name actually dates back to WWII or maybe
even earlier. A "Megger" measures Meghohms, and thus
the name for its use as in "megging a line". I used
them a lot in the service to look for insulation
breakdowns in aircraft wiring. You apply the megger,
which was basically a high voltage generator, crank it
up, and measure the voltage at which current flows, and
then the current, and the readout would in meghohms.
It was a tiny scale, very hard to read, and you usually
got to use it in the mid day tropical sun, inside a
hell hole somwhere in one of the aircraft fuselage.
Just for grins, I jumped onto Google and the first
place I tried turned up one very similar to the ones we
had:
http://physics.kenyon.edu/EarlyAppa...ger/Megger.html
Megger is the actual name of the instrument: try a
search on Google and you'll find lots of hits for
"megger".
They've taken a much more modern design and
application of course, but the concept of all of them
seems to be the same: measuring current flow at
specified voltages and reading out the reults, in
resistance or impedance, whichever the case may be.
It was a surprise to me to see a megger used for ground
rod testing, but I did see a couple of links for that
purpose too, though I didn't open them. I would have
thought it more of a high current test, but apparently
not, which I can sort of see, because the two opposing
phases coming into a building each add or subtract for
total current, depending on the phase, but I can't
argue with facts, eh?
Earth grounds are "interesting' to say the least.
HTH,
Pop
| |
| ~^Johnny^~ 2005-07-24, 9:10 pm |
| -----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
On Fri, 22 Jul 2005 18:35:12 -0400, "Pop"
<nobody@devnull.spamcop.net> wrote:
>A "Megger" measures Meghohms
I'd hate to think of terror measures
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=/OWX
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--
-john
wide-open at throttle dot info
| |
| deans@wdeans.com 2005-07-24, 9:10 pm |
| Greetings,
Everyone here says that #6 is the size ground that you need. I think
that it is important to point out that you actually only need a #8.
The problem is that #8 wire is so small that if you use it you must
protect it from physical damage by placing it into a proper conduit or
by purchasing an armored grounding cable. I often use a #8 ground when
there is no lug which can accept a #6 ground. Please note that just
because a #6 ground will fit doesn't mean the connector is rated for
it! This would be a code violation.
Hope this helps,
William
| |
| George E. Cawthon 2005-07-24, 9:10 pm |
| Pop wrote:
> "George E. Cawthon" <GeorgeC-Boise@worldnet.att.net>
> wrote in message
> news:qadEe.23571$5N3.9037@bgtnsc05-news.ops.worldnet.att.net...
>
>
> ...
> I think the name actually dates back to WWII or maybe
> even earlier. A "Megger" measures Meghohms, and thus
> the name for its use as in "megging a line". I used
> them a lot in the service to look for insulation
> breakdowns in aircraft wiring. You apply the megger,
> which was basically a high voltage generator, crank it
> up, and measure the voltage at which current flows, and
> then the current, and the readout would in meghohms.
> It was a tiny scale, very hard to read, and you usually
> got to use it in the mid day tropical sun, inside a
> hell hole somwhere in one of the aircraft fuselage.
>
> Just for grins, I jumped onto Google and the first
> place I tried turned up one very similar to the ones we
> had:
> http://physics.kenyon.edu/EarlyAppa...ger/Megger.html
>
> Megger is the actual name of the instrument: try a
> search on Google and you'll find lots of hits for
> "megger".
> They've taken a much more modern design and
> application of course, but the concept of all of them
> seems to be the same: measuring current flow at
> specified voltages and reading out the reults, in
> resistance or impedance, whichever the case may be.
>
> It was a surprise to me to see a megger used for ground
> rod testing, but I did see a couple of links for that
> purpose too, though I didn't open them. I would have
> thought it more of a high current test, but apparently
> not, which I can sort of see, because the two opposing
> phases coming into a building each add or subtract for
> total current, depending on the phase, but I can't
> argue with facts, eh?
> Earth grounds are "interesting' to say the least.
>
> HTH,
>
> Pop
>
>
>
Thanks!
| |
| Bill Davis Jr 2005-07-24, 9:10 pm |
| Thanks for the replies all.
Never heard of a megger before. Learn new things everyday.
Bill
| |
|
|
"Bill Davis Jr" <me@home.com> wrote in message
news:63c4e11h0qlm26mt3cs3r1bgf6dvbsm6og@4ax.com...
> Thanks for the replies all.
>
> Never heard of a megger before. Learn new things everyday.
>
> Bill
Next subject-"growlers"....
| |
| CL (dnoyeB) Gilbert 2005-07-24, 9:11 pm |
| > It was a surprise to me to see a megger used for ground
> rod testing, but I did see a couple of links for that
> purpose too, though I didn't open them. I would have
> thought it more of a high current test, but apparently
> not, which I can sort of see, because the two opposing
> phases coming into a building each add or subtract for
> total current, depending on the phase, but I can't
> argue with facts, eh?
> Earth grounds are "interesting' to say the least.
>
> HTH,
>
> Pop
>
>
>
I thought municipal power was 3 phase?
--
Respectfully,
CL Gilbert
| |
| ~^Johnny^~ 2005-07-24, 9:11 pm |
| -----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
On Sun, 24 Jul 2005 01:09:14 -0400, "CL (dnoyeB) Gilbert"
<Fake@ThisOneIsFake.com> wrote:
>
>I thought municipal power was 3 phase?
Distribution is 3 phase, but only a single phase is usually brought
into a residential service.
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=irl6
-----END PGP SIGNATURE-----
--
-john
wide-open at throttle dot info
| |
|
|
"~^Johnny^~" <nospam@gyrogearloose.com> wrote in
message
news:nsg6e1pii9k26kv80q76a9jqc50jrebfpa@4ax.com...
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On Sun, 24 Jul 2005 01:09:14 -0400, "CL (dnoyeB)
> Gilbert"
> <Fake@ThisOneIsFake.com> wrote:
>
>
>
> Distribution is 3 phase, but only a single phase is
> usually brought
> into a residential service.
....
That's true; it isn't really two "phases" per sae.
There are two wires coming to the house from the
transofrmer on the pole, and the literal phase of the
voltage/current is 180 degrees out of phase in each
wire. When one wire is at max voltage in above ground,
the other is at max below ground.
Technically it's called split-phase since it's a
transformer generated relatioship where each wire is
180 degrees out of phase with the other.
Here's a page that does a decent job of describing how
it comes oritinally as 3 phase (120 degree phase
related) and becomes a split-phase derived sigle-phase
power.
That's why so many people refer to it as two-phase.
There ARE two "phases", but ... it's derived from
single phase by splitting that phase.
HTH,
Pop
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| G Henslee 2005-07-24, 9:11 pm |
| Poop wrote:
>
> Here's a page that does a decent job of describing how
> it comes oritinally as 3 phase
Yeah? Where?
Shit your drawers again ya old bastard...
| |
| HorneTD 2005-07-24, 9:11 pm |
| CL (dnoyeB) Gilbert wrote:
>
> I thought municipal power was 3 phase?
>
The power to most homes in North American practice is single phase 240
volt that has been center tapped to derive 120 volts from it. That
system is called an Edison circuit and that is why it is used here. It
was developed for use in converting Edison Electrics DC three wire
circuits to AC. No matter what anyone tells you it is only single
phase. The clearest evidence of which is that there is no way to wire a
motor to it that will make the motor turn without the motor having a
starting capacitor. The power on the supply side of the transformer
that supplies most homes here is often three phase but only one phase is
used to supply each transformer.
--
Tom Horne
Well we aren't no thin blue heroes and yet we aren't no blackguards to.
We're just working men and woman most remarkable like you.
| |
| ~^Johnny^~ 2005-07-24, 9:12 pm |
| -----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
On Sun, 24 Jul 2005 09:51:16 -0400, "Pop"
<nobody@devnull.spamcop.net> wrote:
>
>"~^Johnny^~" <nospam@gyrogearloose.com> wrote in
>message
>news:nsg6e1pii9k26kv80q76a9jqc50jrebfpa@4ax.com...
>...
>
>That's true; it isn't really two "phases" per sae.
>There are two wires coming to the house from the
>transofrmer on the pole, and the literal phase of the
>voltage/current is 180 degrees out of phase in each
>wire. When one wire is at max voltage in above ground,
>the other is at max below ground.
> Technically it's called split-phase since it's a
>transformer generated relatioship where each wire is
>180 degrees out of phase with the other.
>
>Here's a page that does a decent job of describing how
>it comes oritinally as 3 phase (120 degree phase
>related) and becomes a split-phase derived sigle-phase
>power.
> That's why so many people refer to it as two-phase.
>There ARE two "phases", but ... it's derived from
>single phase by splitting that phase.
It can be proven that it is single phase, because the two winding
halves are in series, and during each alternation, current flows
through one half, past the center tap (neutral, common), and
continues in the same direction through the other half. The voltages
add. It they were out of phase, they would buck, and cancel. The
total current always changes direction at the same time, and flows
in the same, continuous direction during each half cycle. However,
due to the center tapped common reference point, the voltages are
instantaneously opposite in polarity in respect to neutral.
They are not out of phase, because their periods are not derived
from alternate zero crossings along the time domain.
I am sorry for the use of the term "phase inverter", in electronics,
because the inversion is effectual, but not actual. "Phase
splitter" is the more "politically correct" term, IMHO. "Voltage
splitter" or "voltage divider" is actually the most correct term.
In AC power, for all practical purposes, it doesn't matter,
whether it's time shifted or polarity inverted. But with complex
signals, like music and voice signals, the positive waveform is not
the same as the negative half of the waveform, and the waveform is
non repetitive. Phase angle becomes meaningless except at a fixed
fundamental frequency, anyway. But even with a fixed frequency
(repetitive waveform), the positive and negative halves don't
necessarily have to be congruent. Here, combing two opposite
polarity copies of the signal will result in cancellation, but
combining the same signal with itself, shifted 180 degrees in time
and subtracting, may not, since the instantaneous absolute values
of the two halves are not always the same.
This is why I consider the term, "out of phase", when used for home
power, to be technically incorrect, even though it really doesn't
matter, provided the two "phases" are equally loaded.
How's this: Take a single phase, invert it, and you have phase
inversion, but still no phase shift. :-)
*Now* I'm *really* splitting hairs. :-)
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--
-john
wide-open at throttle dot info
| |
| Don Young 2005-07-25, 1:21 am |
| > ............ No matter what anyone tells you it is only single phase.
> The clearest evidence of which is that there is no way to wire a motor to
> it that will make the motor turn without the motor having a starting
> capacitor. The power on the supply side of the transformer that supplies
> most homes here is often three phase but only one phase is used to supply
> each transformer.
> --
> Tom Horne
>
I agree with single phase but not that all AC motors have starting
capacitors. There are series motors, repulsion induction motors, split phase
motors, shaded pole motors, and probably others which start and operate on
single phase power without capacitors. Except for the series motor, they all
do use some sort of system to develop an out of phase magnetic field for
starting. Once running only a single phase field is required. Incidentally,
a 180 degree out of phase field, even if derived by phase shifting rather
than inversion, will not start an induction motor. There are two phase
motors which operate with a 90 degree out of phase power source but they are
rather specialized.
Don Young
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