| 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.
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 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.
If I am forced to put GFCI protection in the breaker along with the AFCI
protection, or if GFCI receptacles don't actually have neutral contacts
that can be opened, I do have a fallback plan. I would run the circuit
through a secondary box containing a 2-pole normally open electrically
closed contactor. The circuit would run through these contacts. The
coil would be powered from the supply side. If the breaker opens the
hot wire, the coil will de-energize and open both wires. It won't be as
quick an open since such contactors aren't listed for GFCI protection.
But at least it will be something that can prevent certain problems.
For shared neutral circuits, this would be a 3-pole contactor with a 240
volt coil. These are avalable from Square-D and Cutler-Hammer. One issue
that some people might be concerned with is the constant power used by the
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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