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I have a mobile home that has an outdoor box which is just used as a main 200 amp breaker and spaces for 6 breakers. One double 20 amp breaker is used for 220v pump circuit which the pump installer used 12-2 romex with ground in PVC conduit. There is just one ground bar where the bare ground wire attached. I have two sheds and wanted to put separate 110v in them. Installing a 20 amp dual breaker(both white and ground to same bar) I ran 12-3 with ground UF cable out between the sheds. I installed an outdoor box with a GFI and 110v (black wire) in the shed for grinder/cordless chargers. All working well. Today I used the red with the ground and neutral to a GFI recpt. in the second shed. I have an octagon box below the first GFI where I did all the connections. I had a float charger in the second shed GFI and as soon as I connected the load red to the red to the second shed with the float charger the black circuit kicked off. Baffled me. Is this a phase issue, ground/neutral or something I'm missing. Thanks and God bless.

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  • I would check with a different load. The reason multiwire branch circuits have gone out of fashion is for false tripping. I would test it with a different load as your float charger may be the cause. – Ed Beal Nov 5 '20 at 23:58
  • How is the pump circuit related to the shed circuits? Are the shed circuits daisy-chained off of the pump circuit? If so, where are the breakers? A sketch showing the main panel, the pump circuit (with breaker) and the shed circuits (with breakers) would help a lot. Doesn't have to be fancy, just neatly drawn then upload a picture taken with your phone will do. – FreeMan Nov 6 '20 at 13:28
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You tried to poach the second shed's neutral from the GFCI protection on the first shed, so its no wonder the first GFCI tripped

What happened here isn't as weird-sounding as you are thinking it is. You just need to remember two fundamentals here: first, that electric current flows in loops (it always has to make it back to the utility, generator, battery, or so on) and second, that a GFCI has nothing to do with ground as it simply compares what went through it on the hot side with what went through it on the neutral side and trips if they don't match up.

This all adds up to this being a simple wiring error; namely, that you tried to tap neutral to the second shed from the load side of the GFCI in the first shed. As a result of this, when you tried to use the receptacle in the second shed, you injected the charger's running current, taken from the red wire (which the first shed's GFCI has no clue about) into the load neutral terminal of the first shed's GFCI. Said GFCI sees this inexplicable-to-it flow of current on neutral, goes "WTF?!", and trips, just as it's designed to do, thinking something is wrong, which is true.

Fortunately, the fix here is simple; you just need to move the neutral connection going off to the second shed to the LINE side of the first shed's GFCI. Note that you'll probably want disconnect-rated GFCIs here if you don't have them already (they're denoted by having ON/OFF labeling on their buttons to go with the normal TEST/RESET labeling).

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  • hey A3PE, wouldn't wiring from the Line side of said GFI make using the disconnect feature moot? – Jimmy Fix-it Nov 6 '20 at 0:46
  • Thanks for that. Iv'e installed a lot of GFI"s before and ner heard of – Grampie Gram Nov 6 '20 at 0:47
  • d of/noticed "disconnect-rated GFCI. It just has a test and reset buttons. I am going to get another gfi for the 2nd shed but I just has a regular recpt in for the float charger. BTW the 1st shed is using the " load" terminals on the black wire side GFI for shed light/chargers. – Grampie Gram Nov 6 '20 at 0:59
  • @JimmyFix-it -- basically, it depends on your definition of power "passing through" a structure, but I don't think the OP wants turning off the first shed at the shed to turn off a different structure somewhere else – ThreePhaseEel Nov 6 '20 at 1:41
  • yes, I agree. To prevent imbalance trip on upstream GFI on MWBC he needs to pull from LINE side with at least the nuetral, but in that case using a disconnect-rated GFI becomes a moot point because you cannot completely isolate downstream using the buttons... cuz you're wired to the Line side. Or I could easily be missing something here lol... – Jimmy Fix-it Nov 6 '20 at 1:58

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