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2-pole GFCI breaker for Edison (shared neutral) circuit
wrote:
For complicated reasons (see below), I need to run two 120V 20A outlet
circuits as an Edison circuit (shared neutral), and they have to be
protected by GFCIs. I can't just use GFCI outlets.
If this were a single 120V circuit, I could do this by using the load
lugs on a GFCI. But for an Edison circuit, I can't simply use two
GFCIs (they will trip all the time, as the neutral conductor would be
shared on the load side, and they will see the load on the other side
as a fault current).
Questions: Will a 2-pole 20A GFCI breaker work? Or are those designed
purely for balanced 240V loads, and the GFCI will trip when unbalanced
load is applied via one of the 120V outlet circuits?
Explanation of what I mean and why this is needed. An Edison circuit
is two 120V circuits, wired using a shared neutral, and fed from the
two opposite phase hot legs (I don't want to start a useless debate
whether 240V is split phase or two phase, you know what I mean). This
works because under full load, the neutral currents cancel, so the
single neutral is not overloaded (you can have 20A on both of the hot
legs of the circuit, without overloading the third neutral conductor).
Usually I don't do this, because (a) more copper is a good thing, (b)
what happens if someone rearranges the breakers, and by mistake puts
both hot legs on the same phase, and (c) what happens when the whole
house is run from a single-phase 120V generator via a large transfer
switch temporarily (hint: in cases (b) and (c) the neutral conductor
overloads, and may start a fire).
Why do I have to run an Edison circuit? Because I want to install
surface raceway outlet strips along all the walls; this particular
model is made by Wiremold. You have probably seen those: They are a
two-part sheetmetal conduit, with regularly spaced outlets. They are
rated for 20A at 120V, with two circuits alternating at 1' spacing.
This is going to make for extremely convenient outlet placement
(everywhere), but the Wiremold strips are Edison wired.
SNIP
BTDT
The Wiremold is an excellent choice for this app.
The 2-pole GFCI breaker will work perfectly here;
it does not require a balanced load.
There is *no* requirement that each circuit be
protected by an individual breaker.
(There *is* a requirement that both circuits trip
together (2-pole handle tie) under *some* circumstances
in the NEC. Not applicable to this discussion..)
Jim
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