AFCI/GFCI in subpanel

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codetalker

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When a AFCI/GFCI is installed in a subpanel, where does it get it's ground reference? Even if it's not a GFCI, all the combination AFCI's have gfci circuits. Thanks
 
The EGC goes back to main panel/disconnect where the neutral/grounded conductor and GEC, grounding electrode conductor, are tied together and EGCs are derived.

Since the sub panel is bonded by the feeder EGC from the supply/main panel, your reference for 120V to ground is created.
 
I get that. I know it bonds at the main panel. Lets just talk GFCI; I was trying to think thru the current flow if GFCI current output connects to the neutral. The neutral from main to sub could have a bunch of current flowing, it seems like that would affect the GFCI. Maybe that's why there is a wire to neutral on AFCI/GFCI breakers.
 
The white wire pigtail on AFCI/GFCI breakers is for the electronic circuitry in the breakers to operate. It also completes the circuit.

If you had a 2 pole AFCI or GFCI breaker and a 240V load that did not use a neutral for 120V, you would still need to put the pigtail into the neutral bus for the breaker to operate. There would be no circuit neutral to put on the breaker.
 
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There's nothing special about the current paths with the GFCI breaker, except that the breaker intercepts the neutral return path for the circuit, in addition to switching/breaking the ungrounded conductor.

Here's some bad ASCII art for the 1-pole case:

Code: 
L1 Bus ------- Regular Breaker ----------
                                        |
                                      Load
                                        |
N Bus -----------------------------------


L1 Bus ------- GFCI ---------------------
               Breaker                  |
               With Neutral            Load
               Routed                   |
N Bus ---------Through It----------------

Cheers, Wayne
 
codetalker said:
When a AFCI/GFCI is installed in a subpanel, where does it get it's ground reference? Even if it's not a GFCI, all the combination AFCI's have gfci circuits. Thanks
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The "ground reference" really doesn't have anything to do with how a ground fault is detected. The current flowing in the hot conductor is compared to the current flowing in the return conductor. Under normal conditions the two currents are equal, but flowing in opposite directions. When the hot and return currents differ, by as little as 5 milliamps, the circuit interrupter operates.

There is no knowledge of where the missing current (the difference) is traveling. . . ALL of the ground fault detection happens within the device.
 
Or maybe a pic? IDK.

gfci-afci-circuit-breaker-wiring-diagram.png
 
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