On 06/06/2014 03:08 PM, Lee Hart wrote:
Haudy Kazemi via EV wrote:
Schneider Electric says some kinds of GFCI breakers are not backfeed
friendly and can in fact damage them:
http://static.schneider-electric.us/docs/Circuit%20Protection/0900DB1001.pdf
---start quote---
These circuit breakers are distinctive in that they have a white
“pigtail” wire intended for connection to the neutral bar in the
panelboard in which they are installed. This pigtail wire not only
completes the branch circuit (the neutral wire must be connected to the
circuit breaker rather than to the neutral bar), but also completes the
power supply circuit for the electronic ground fault detection
circuitry.
Backfeeding (reverse connecting) these circuit breakers will result in
damaging the trip solenoid, rendering the ground fault trip function
inoperative. For this reason the terminals on these circuit breakers are
marked “line” and “load”.
That's not the kind of backfeeding that a grid-tie inverter or EV
doing V2G uses.
A GFCI is a switch, a solenoid, and a control circuit. You have to
manually turn the switch on. When the control circuit detects a fault,
it connects the solenoid to the *output* side of the GFCI. Since there
is power there, the solenoid yanks the switch to turn it off. Now
there is no power on the output, so the solenoid is off, too. Thus the
solenoid cuts its own power.
If you connect such a GFCI backwards, then it does *not* turn off
power to its solenoid when it trips. The solenoid coil stays powered,
and burns up.
But a grid-tie inverter or V2G EV will automatically quit backfeeding
if it sees the grid go away. This also removes power from the GFCI's
solenoid.
Thanks Lee, this explanation makes sense. It reconciles what is
published by some manufacturers with what has been said here (that
backfeeding can be done with GFCIs). The clarified answer is that GFCI
solenoid damage risk exists with some types of GFCIs when they're used
in combination with some types of backfeed through the GFCI. The
problematic type of backfeed would include generators and offgrid
inverters that operate independent of a grid-supplied voltage and
frequency reference. Safe backfeed sources are those that only backfeed
when they detect that an appropriate grid-supplied voltage and frequency
reference is available (and thus shut themselves off when islanded from
their reference).
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