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Posted by Bud-- on September 29, 2006, 12:00 pm
phil-news-nospam@ipal.net wrote:
>
> | Those without GFCI protection are intended for use in habitable and
> | non-habitable spaces not requiring ground fault protection (living rooms and
> | the like.)
> |
> | Those with 5ma GFCI protection are intended to serve bathrooms, kitchens and
> | anywhere where a standard GFCI is required.
> |
> | Those with 30ma GFCI is designed to serve residential equipment noted in the
> | NEC requiring 30 ma GFCI (actually termed GFEP to differentiate between the
> | two.) Article 426.28 only requires ground fault protection for equipment, no
> | personnel and that's to only place it can be used to meet code. To protect
> | personnel, you must use 5ma protection.
>
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). Arcs can produce carbon paths which, if a ground is available,
can produce ground fault currents. That may produce a trip before there
is an arc or before an arc is detected.
In the Consumer Product Safety Commission paper at:
http://www.cpsc.gov/volstd/afci/AFCIFireTechnology.pdf
that is explained on pdf page 14.
Phil has a link in another thread to:
http://www.eatonelectrical.com/unsecure/cms1/AFCI_UL_SPECIAL_SERVICES_INVESTIGATION.PDF
which is a UL investigation showing that a "glowing connection" at a
receptacle binding screw may (or may not) cause an AFCI trip through
the 30mA ground fault function.
> This is along the lines of what I expected, and certainly sounds very
> reasonable. Still, the required ground fault protection can be had with
> an AFCI that has no GFCI, or only has 30ma GFCI, as long as the 5ma GFCI
> receptacles are also used, where the GFCI people protection is required.
> Whether one would want to do it that way is another matter.
>
> In a bathroom, there is an advantage to having the ability to reset the
> GFCI device right there. That advantage may or may not be relevant for
> a kitchen. Other areas like a garage are probably not much of a concern.
>
> 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?
>
I have read in newsgroups (so it must be true) that both poles are
opened for hot-neutral-reverse protection.
GFCIs (5mA) are now required to not work with reverse load-line terminal
wiring. (Previously the load terminals connected to the receptacle.) I
don't think you can do that without double pole contacts line-receptacle
and line-load. And I don't think it can be done without that being a NO
contact that requires the device to be powered to connect (which it
wouldn't be if the line-side neutral was open).
In both cases testing can be easily done without a hammer but so far I
have been too lazy.
> I do believe some neutral wire risk exists. It's certainly not as much as
> for the hot wire, usually in terms of voltage, and in terms of exposure
> events. One example of when the risk is high is when there is a open in
> in the supply neutral. But the chance of that happening coincident with
> contacting the neutral to ground, is much lower than either alone. The
> other risk is the voltage present as a function of the voltage drop along
> the supply neutral from the point of bonding to the point of contact.
> That's generally a very low voltage, though it can vary with loading on
> the system. Still, I'd feel safer having an interruption mechanism that
> will open BOTH wires together when tripped.
>
> Suppose you have an AFCI that includes GFCI protection, either at the 5ma
> level or the 30ma level, followed by a GFCI receptacle. Leakage from the
> neutral to ground would still result in a trip. But can it be guaranteed
> that the receptacle device will always open? Perhaps the breaker will open
> first, and de-energize the circuit before the receptacle can open, leaving
> the neutral wire still connected. To be assured that the receptacle will
> trip, I'd have to have no GFCI in the breaker, and place the GFCI protection
> in the receptacle, assuming it is designed to open the neutral.
>
bud--
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