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Posted by on September 30, 2006, 8:48 am
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|> 30mA ground fault detection in an AFCI is for arc protection. Far as I
|> know all AFCIs include it (though I need to look harder at phil's 2nd
|> link).
|
| Here's a good place to learn more.
|
http://www.cpsc.gov/CPSCPUB/PUBS/afcifac8.pdf#search=%22afci%20ground%20fault%22
Sounds like we are now back to the beginning.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2006-09-30-0748@ipal.net |
|------------------------------------/-------------------------------------|
|
|
Posted by PPS on October 2, 2006, 7:40 pm
A "neutral" is not defined in the NEC, but is described in Article
310.15(B)(4) as carrying "only the unbalanced current from other
conductors...".
In a 120 volt (lighting) circuit, the current is carried on both the white
(or "grounded") conductor and an "ungrounded (usually black, but not
necessarily) conductor.
The term "neutral" refers to the neutral connection at the transformer; the
center-tap. In a pure 240 volt circuit, current flows on the two phase
conductors and a white (or grounded) conductor in not even needed. By
introducing 120 volt circuits, the white forms one of the return legs, and
carries current. (240 v between the ungrounded legs, 120 v from either leg
to the neutral.)
In Europe, the term "neutral" does include a grounded conductor in a 120 v
circuit. In the states the term is used interchangeably but in error.
> |
> |> 30mA ground fault detection in an AFCI is for arc protection. Far as I
> |> know all AFCIs include it (though I need to look harder at phil's 2nd
> |> link).
> |
> | Here's a good place to learn more.
> |
>
http://www.cpsc.gov/CPSCPUB/PUBS/afcifac8.pdf#search=%22afci%20ground%20fault%22
>
> Sounds like we are now back to the beginning.
>
> --
> |---------------------------------------/----------------------------------|
> | Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below
> |
> | first name lower case at ipal.net / spamtrap-2006-09-30-0748@ipal.net
> |
> |------------------------------------/-------------------------------------|
|
|
Posted by on October 4, 2006, 9:09 am
| A "neutral" is not defined in the NEC, but is described in Article
| 310.15(B)(4) as carrying "only the unbalanced current from other
| conductors...".
"Neutral conductor" is defined in the NEC. The term is used in many places.
I fully understand what a neutral is. Are you raising an issue about its
common or formal usage?
| In a 120 volt (lighting) circuit, the current is carried on both the white
| (or "grounded") conductor and an "ungrounded (usually black, but not
| necessarily) conductor.
If you are wanting to get very specific, it's the insulators that have the
color. The current is carried on the (usually) copper metal (with a magnetic
field, of course).
The code requires the grounded conductor be identified well (e.g. continuous
color, not just marked at each end). Others have more leeway.
| The term "neutral" refers to the neutral connection at the transformer; the
| center-tap. In a pure 240 volt circuit, current flows on the two phase
| conductors and a white (or grounded) conductor in not even needed. By
| introducing 120 volt circuits, the white forms one of the return legs, and
| carries current. (240 v between the ungrounded legs, 120 v from either leg
| to the neutral.)
You could tap the transformer off-center a bit if you wanted to and have
115 volts on one side and 125 volts on the other side. Would you call that
a "neutral"?
So tell me ... what happens if you have a couple of very low power factor
loads, one on each 120 volt side, where one is very inductive and the other
is very capacitive? Now how much current flows on the "neutral"?
| In Europe, the term "neutral" does include a grounded conductor in a 120 v
| circuit. In the states the term is used interchangeably but in error.
I see very little use in error in the US. Neutral does not mean grounded,
but it generally implies that because that is the required way to wire it
up. See NEC 250.26(2). The two terms "neutral conductor" and "grounded
conductor" do have different meanings, but are associated with the same
wire because that is the required way.
Single phase in Europe is generally 2-wire service. You can still call one
wire neutral because it may well be the wire connected to the real neutral
point in either a single phase transformer (center tapped 230/460) or a
three phase transformer (connected to the star common). But it is grounded
and thus (also) correct to call it a grounded conductor. If the service is
coming from a 2-wire transformer all by itself, then it's not really neutral;
it's just grounded.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2006-10-04-0750@ipal.net |
|------------------------------------/-------------------------------------|
|
|
Posted by Andrew Gabriel on October 5, 2006, 4:25 am
> In Europe, the term "neutral" does include a grounded conductor in a 120 v
> circuit. In the states the term is used interchangeably but in error.
In Europe, there are no 120V circuits, and "neutral" is a supply
current carrying conductor which is at or near ground potential.
--
Andrew Gabriel
|
|
Posted by on October 5, 2006, 6:51 am
|> In Europe, the term "neutral" does include a grounded conductor in a 120 v
|> circuit. In the states the term is used interchangeably but in error.
|
| In Europe, there are no 120V circuits, and "neutral" is a supply
| current carrying conductor which is at or near ground potential.
But that doesn't really change the meaning's origin. The first power
systems were three phase to drive motors. I don't know if delta was
used much way back when, but with star/wye configurations, you do have
a genuine neutral. When single phase at 240v is taken from that, the
neutral is still there. It just doesn't have enough phases brought
in to take the neutralizing role there.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2006-10-05-0547@ipal.net |
|------------------------------------/-------------------------------------|
|
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