Dose the listing permit an arc fault circuit breaker to supply at GFCI receptacle?

Does anyone have anything on this? Also, does the GFCI reptacle listing permit use on a AFCI circuit?

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On Sun, 24 Dec 2006 16:32:37 -0900, "Gerald Newton"

I don't see anything mutually exclusive in either listing. Nor can I think of a technical reason why their could be a hazard. GFCIs are commonly downstream of other GFCIs with no problem.
The guys over at ECN had this discussion a while ago, referring to serving an outside GFCI receptacle from a bedroom.
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On Sun, 24 Dec 2006 21:31:36 -0500 snipped-for-privacy@aol.com wrote:
| On Sun, 24 Dec 2006 16:32:37 -0900, "Gerald Newton"
| |>Does anyone have anything on this? |>Also, does the GFCI reptacle listing permit use on a AFCI circuit? |> | | I don't see anything mutually exclusive in either listing. Nor can I | think of a technical reason why their could be a hazard. | GFCIs are commonly downstream of other GFCIs with no problem.
Does this ever include a GFCI _receptacle_ downstream from a GFCI _breaker_?
One small problem I do see where a GFCI _receptacle_ is downstrealm from a GFCI -or- AFCI _breaker_ is the risk of electrical shock from the neutral conductor. A GFCI receptacle interrupts both hot and neutral. A breaker generally does not. There are such animals as "switched neutral" breakers typically used for fuel pump circuits where the issue expands to triggering fuel vapor explosions. However, from just an electrical perspective, there is some, small as it is, risk from electrical shock from a neutral. This generally a case of _two_ (or more) things having to go wrong at the same time for this to happen. Not only does someone who is well grounded have to be contacting a neutral (the probability of this being higher than that of contacting a hot wire because of legacy appliances when frames connected to the neutral, assuming a polarized plug), but some situation must also exist that places significant voltage on the neutral. One example is an open neutral on an upstream feeder while opposing poles are way out of balance. Another example is that this contact of the neutral just happens to be when some other device or appliance has a line-to-neutral fault.
If a current imbalance causes the GFCI receptacle to open, both line and neutral conductors will be opened and a safer condition then exists. If this happens with a GFCI or AFCI breaker, then the neutral remains connected _and_ there is no power available to the GFCI receptacle for it to take any action. The (small) extra protection of the GFCI receptacle is thus disabled.
The issue to consider is just how much of a risk this is. I'm sure we all agree it is definitely smaller than the risk of contacting a hot line wire under similar conditions of the person being grounded. But I believe it is certainly a non-zero risk. Your home would be a lot safer from electrocution by just not having electricity at all, though it would now be arguably less safe due to things like fires from errant candles, etc. There is no zero risk scenario; risk has to be managed.
My position is that if you compare the risk between having a GFCI receptacle on an AFCI (with GFCI protection) breaker protected circuit and having just a regular receptacle, you'll find that not having the GFCI receptacle is the greater risk. So even with AFCI breakers serving most of the home, I will continue to have GFCI receptacles protecting at least certain areas like the bathrooms.
I happen to dislike the style of GFCI receptacles for my kitchen. So even before the NEC 2008 decision to expand use of AFCI protection, I have been looking at ways to protect the kitchen without GFCI receptacles. One option is a bank of dead-front GFCI "receptacles" away from immediate view which can interrupt any or all circuits in the kitchen. Since I also expect to have and use 240 volt plug-connected appliances, that approach is not complete. One solution I have is this. I will use GFCI (or now AFCI with GFCI in it) breakers in a subpane near the kitchen. The 2-wire 240 volt circuits will not have a neutral and won't need any more protection since the breaker will cut off both line wires. The 120 volt circuits can become fully protected by one of two means: either the dead-front GFCI "receptacles" in the circuit or a 2-pole contactor providing supplimental protection by opening neutral and line wires when L-N power is lost. A 3-pole contactor could do this for 2 circuits on one yoke (neutral shared to the contactor and powered by a 240 volt coil fed from a 2-pole breaker).
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On 25 Dec 2006 14:33:27 GMT, snipped-for-privacy@ipal.net wrote:

I suppose if this was in a sub panel and the neutral was open it could happen. Having a GFCI outlet down stream would probably make things safer since it would still detect the ground fault and open both sides
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On Mon, 25 Dec 2006 10:29:19 -0500 snipped-for-privacy@aol.com wrote:
| On 25 Dec 2006 14:33:27 GMT, snipped-for-privacy@ipal.net wrote: | |>One small problem I do see where a GFCI _receptacle_ is downstrealm from a |>GFCI -or- AFCI _breaker_ is the risk of electrical shock from the neutral |>conductor | I suppose if this was in a sub panel and the neutral was open it could | happen. Having a GFCI outlet down stream would probably make things | safer since it would still detect the ground fault and open both sides
But if upon a ground fault on that branch, the _breaker_ opens before the _receptacle_ can act to open, the GFCI receptacle will no longer have any power to do it's thing, leaving the neutral fully connected. It's a timing issue there. Maybe the GFCI receptacle will trip first. Or maybe both will trip and the receptacle gets reset and the person doing that wonders why still no power and messes around with things and comes in contact with that neutral that isn't open because the receptacle was reset and the breaker doesn't open the neutral.
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On 26 Dec 2006 02:52:47 GMT, snipped-for-privacy@ipal.net wrote:

You are right that a GFCI breaker will not protect from a hot neutral but there are lots of terrible things that happen with a bad neutral. I suppose that is why we should be very careful making up neutral and grounding connections. Maybe as a practical issue you should never install a GFCI breaker in a sub panel This still would only affect a sub panel. That is the reason why you couldn't use the neutral for a ground on a dryer or range when that was legal.
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On Mon, 25 Dec 2006 22:34:54 -0500 snipped-for-privacy@aol.com wrote: | On 26 Dec 2006 02:52:47 GMT, snipped-for-privacy@ipal.net wrote: |
|>
|>| |>|>One small problem I do see where a GFCI _receptacle_ is downstrealm from a |>|>GFCI -or- AFCI _breaker_ is the risk of electrical shock from the neutral |>|>conductor |>| I suppose if this was in a sub panel and the neutral was open it could |>| happen. Having a GFCI outlet down stream would probably make things |>| safer since it would still detect the ground fault and open both sides |> |>But if upon a ground fault on that branch, the _breaker_ opens before the |>_receptacle_ can act to open, the GFCI receptacle will no longer have any |>power to do it's thing, leaving the neutral fully connected. It's a timing |>issue there. Maybe the GFCI receptacle will trip first. Or maybe both |>will trip and the receptacle gets reset and the person doing that wonders |>why still no power and messes around with things and comes in contact with |>that neutral that isn't open because the receptacle was reset and the |>breaker doesn't open the neutral. | | | You are right that a GFCI breaker will not protect from a hot neutral | but there are lots of terrible things that happen with a bad neutral. | I suppose that is why we should be very careful making up neutral and | grounding connections. Maybe as a practical issue you should never | install a GFCI breaker in a sub panel
Or an AFCI breaker that has GFCI functionality.
| This still would only affect a sub panel. That is the reason why you | couldn't use the neutral for a ground on a dryer or range when that | was legal.
I would disagree. While on a sub panel the risk is higher, on a main panel the risk is non-zero. Even if the grounds don't fail, you could still have some small ground differential voltage because there is also a ground at the source transformer. But, in almost all cases, not enough to worry about. Still, I'm considering a full isolation transformer for my house so I have an isolated system that is clearly ground bonded at exactly one point.
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On 26 Dec 2006 11:51:33 GMT, snipped-for-privacy@ipal.net wrote:

They make them. All AFCIs have GFP (30ma) protection. Some even have 5ma protection.

The ground electrode system is there to assure that even if there is some rise above ground in the neutral it will be reflected on the local ground plane, bonded plumbing, EGCs etc. If you have a Ufer GES that will include the concrete floor. In a sub panel that neutral could be significantly above ground
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On Tue, 26 Dec 2006 12:04:22 -0500 snipped-for-privacy@aol.com wrote: | On 26 Dec 2006 11:51:33 GMT, snipped-for-privacy@ipal.net wrote: | | |>| You are right that a GFCI breaker will not protect from a hot neutral |>| but there are lots of terrible things that happen with a bad neutral. |>| I suppose that is why we should be very careful making up neutral and |>| grounding connections. Maybe as a practical issue you should never |>| install a GFCI breaker in a sub panel |> |>Or an AFCI breaker that has GFCI functionality. |> | They make them. All AFCIs have GFP (30ma) protection. Some even have | 5ma protection.
I don't know about all manufacturers, but Cutler-Hammer makes them with no GFCI as well as both 30ma and 5ma, and in both 1-pole and 2-pole.
Well, I do know Square-D doesn't have such variety.
|>| This still would only affect a sub panel. That is the reason why you |>| couldn't use the neutral for a ground on a dryer or range when that |>| was legal. |> |>I would disagree. While on a sub panel the risk is higher, on a main panel |>the risk is non-zero. Even if the grounds don't fail, you could still have |>some small ground differential voltage because there is also a ground at |>the source transformer. | | The ground electrode system is there to assure that even if there is | some rise above ground in the neutral it will be reflected on the | local ground plane, bonded plumbing, EGCs etc. If you have a Ufer GES | that will include the concrete floor. In a sub panel that neutral | could be significantly above ground
Even with a well grounded and well bonded main panel, someone touching the neutral and earth will become "one of many paths" back to the system source. The closer their earth contact is to the main electrodes, the less significant that path will be. The service drop neutral will, of course, be the primary path. The main panel ground electrodes through earth and back to the pole or pad transformer electrodes is another. And the victim makes a 3rd. How significant? If all is working well, there shouldn't even be a tingle. But if things go wrong ...
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On 27 Dec 2006 02:47:28 GMT, snipped-for-privacy@ipal.net wrote:

I suppose you could petition NFPA, NEMA and U/L with your concerns but I don'tr see a big chance of changing the way they make GFCI/AFCI breakers. If you can really make the case they might go for it.
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On Tue, 26 Dec 2006 23:40:41 -0500 snipped-for-privacy@aol.com wrote: | On 27 Dec 2006 02:47:28 GMT, snipped-for-privacy@ipal.net wrote: | |>Even with a well grounded and well bonded main panel, someone touching |>the neutral and earth will become "one of many paths" back to the system |>source. The closer their earth contact is to the main electrodes, the |>less significant that path will be. The service drop neutral will, of |>course, be the primary path. The main panel ground electrodes through |>earth and back to the pole or pad transformer electrodes is another. |>And the victim makes a 3rd. How significant? If all is working well, |>there shouldn't even be a tingle. But if things go wrong ... | | I suppose you could petition NFPA, NEMA and U/L with your concerns but | I don'tr see a big chance of changing the way they make GFCI/AFCI | breakers. If you can really make the case they might go for it.
I don't really see a course that I'd want them to take. If I were in their shoes, what would I do? I really don't know.
One thing I do think is needed:
A redesign of the bussing architecture of breaker panels. The neutral show be included as one of the pluggable busses, such as out both outer sides of the busway area. With so many AFCI breakers soon to be going into breaker panels, certain issues will be cropping up. One of those is the increased packing of greater heat dissipating devices. The other is an increase in the number of neutral wires going from the neutral bus bar to the breaker, and then from the breaker to the circuit cable. A little more wiring density and less neat panel makeup. If a whole new panel bus architecture adds a neutral pluggable bus (not part of the interleave between lines, but rather, available on every slot), breakers can make both line and neutral contact when plugged in, and have terminals for both without the extra wire to connect back to a neutral bus. That can be done in one slot per pole for some breakers (AFCI) and in one extra slot for certain others (switched neutral breakers where that is needed). That would just leave grounding with a separate terminal bus (and IMHO, should be run the full length of the panel on both sides).
I'd like to see a standards agency like NEMA design it and specify how tight comformance can be determined for each component so that it will not be necessary for every part to literally be tested in every panel for a listing that allows any part to be used in any panel (e.g. no special "classified breakers" listing as is done now with competitive breakers). This should still be an architecture that will allow for both 2-pole and 3-pole services with the same breakers working in either. But these should be an all new size to avoid cross fitting to what is commonly used now. I'd pick 2cm for the slot width for branches up to 125 amps.
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On 27 Dec 2006 11:19:43 GMT, snipped-for-privacy@ipal.net wrote:

I would want a lug connection for the neutral, not a stab
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