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Posted by Member, Takoma Park Volunteer on October 1, 2006, 1:14 pm
phil-news-nospam@ipal.net wrote:
> | PPS wrote:
> |>>I have been told, but have never sacrificed a device to verify, or set up
> |>>the appropriate test, that GFCI receptacles open BOTH the hot wire AND the
> |>>neutral wire when they trip. If so, why is that? Is it to offer at least
> |>>some protection even when the device is miswired? Or is there even some
> |>>risk with voltages on the neutral wire?
> |>
> |>
> |> Just opens the ungrounded conductor, not the ground (mistakenly called a
> |> neutral).
> |
> |
> | The grounding conductor is irrelevant to GFCI operation.
> | Both the neutral and the hot are interrupted when
> | a GFCI receptacle trips.
>
> So why is the neutral opened? That's an "academic question" (I can come up
> with what I think are good reasons to do so). Now, considering answers to
> this question, what protections might be lost if AFCI breakers that include
> GFCI protection at the 5ma level result in GFCI receptacles not being used?
> Is GFCI protection in a breaker considered adequate for the requirements in
> NEC 210.8 even though it does not open the neutral connection? Would YOU
> persoanlly feel less safe if all the receptacles in a kitchen were protected
> for ground fault leakage only by circuit breakers at the panel (assume that
> the panel is close by).
>
> There must be _some_ reason _they_ chose to include opening the neutral in
> GFCI receptacles (maybe more than one). But wouldn't such reasons also be
> applicable to circuit breaker based protection?
>
> What if you have _both_ GFCI protection at the breaker _and_ GFCI protection
> at the receptacle, say in a bathroom. Now suppose there is a slight leakage
> fault, but only the breaker opens on it. Maybe the receptacle was going to
> interrupt the fault, but was just sufficiently slow, perhaps due to a slow
> rise in the leakage current, that the breaker did it first, which prevents
> the receptacle from doing so. Now you have a condition where the neutral
> continues to be fully connected all the way from the main panel, through
> the GFCI receptacle that no longer has power on it's hot wire, and into the
> plugged in appliance that someone grabbed with a dripping wet hand while
> also grabbing a towel out of the basin water in the sink.
>
> Well, usually, a neutral doesn't have much voltage relative to ground. But
> if there was some kind of open neutral condition also present (now we are at
> the level of _two_ existant problems) and a rather unbalanced load between
> the two single phase poles (somewhat common), we could be dealing quite many
> volts still available through the GFCI receptacle that didn't trip because
> it lost power due to the ground fault that was detected by the breaker first.
>
> So my thinking here is, if there is protection to be gained by opening the
> neutral at GFCI receptacles, we should _not_ be requiring that AFCI breakers
> be of the type that combine GFCI protection. And perhaps such breakers
> should be prohibited for these circuits.
>
> Of course there is also the issue of the inconvenience of going all the way
> to the breaker panel to reset a ground fault. This could be particularly
> so for bathrooms (imagine being dripping wet, wearing only a towel, going
> out to the garage or down to the basement, standing on a concrete floor,
> to reset a breaker).
>
What makes you so certain that a GFCI circuit breaker does not open the
neutral? Have you checked with several manufacturers.
One reason why it might be OK for a breaker to leave the neutral alone
is that it is far less likely and in fact rather difficult for a breaker
to be revere wired. When a breaker type GFCI operates it will nearly
always open the ungrounded conductor. There are a lot more ways a
receptacle type of GFCI can be supplied with the ungrounded conductor
controlled by the grounded conductor leg of the GFCI mechanism.
--
Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison
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