Electrical Challenge of the Day: GFI tripping

[LD1]

Seems we have several electrical buffs on the forum. So this is kinda a challenge to see who can figure this out. One of the "to-do's" on my list after the inspection (before I can close on selling), Was the bathroom GFI. The inspector said it didnt trip when he used his 5mA tester. So....

I work nights. Got home this AM at 8. Pulled out the GFI to replace it And noticed all wires were on the line side, thus bypassing the GFI:confused2: So after uwiring and determining which is line, I rewired the GFI and re-installed. Now, everytime I turn the closet light on, it trips.

So, I kill the bathroom again, thinking maybe its a bad GFI and thats why they bypassed it, I go to replace it with the new one I bought. Then I felt that little tingle when unwiring. Sure enough, the load side had juice to it now for some reason. So I kill the power to the master bedroom. Rewired, and turned breakers back on. Same thing. Trips when master closet light comes on. So I start testing around on GFI line and load wires and I have 240V under certain conditions

Here is a crappy paint drawing of how things are wired. Hopefully you can understand it. NOW, The challenge: See who can figure out the cause. Off to bed now, will give the answer this afternoon or so when I wake.

 

[k0ua]

goofy shared neutral path on the switched outlet.. Why was that done..? So unbalanced path.

 

[newbury]

<snip>So I start testing around on GFI line and load wires and I have 240V under certain conditions
<snip>

Single phase :

Now you can power up a welder!

 

[k0ua]

yeah, two sequentially numbered breakers in a box are going to be on separate phases.. and for that matter, why are receptacles and lighting circuits mixed anyway in that drawing?

 

[buickanddeere]

A single pole GFI can not share a neutral. Of course it will trip when line and neutral current are not balanced.
Just supply the closet light from the line side of the GFI.

 

[CobyRupert]

goofy shared neutral path on the switched outlet.. Why was that done..? So unbalanced path.

Yes. A little background info to OP: A GFI needs to see the same current going in/out on the "hot" (black wire) side as it sees returning on the neutral (white wire) side. If the current isn't balanced (within 3-5 milliamps) it thinks current is leaking somewhere (a short) and trips. Because you have 2 paths for the neutral current (connected at the switched recept) to return to the panel, the neutral current splits and GFCI doesn't see the same amount of neutral current as "hot" leg current.

What doesn't make sense, as per your diagram, is getting 240V at GFCI. This can only happen when you're somehow measuring between ckt. 26 & 27. Are you sure circuit 26 & 27 aren't connected at the switched outlet and end up at the GFCI?

The other way the GFCI could see 240V is if:
The neutral for ckt. 26 is disconnected (or loose) and floating, when the closet light is "on" (but no current, so bulb is not lit), the switch is closed, the GFCI is opened you can have 120V from ckt 26 passing through the light (but there's no voltage drop because there is no current, no current return path, bulb is dim) and 120V (to ground) will be present at the GFCI on (the "floating") neutral wire that is connected to the closet light. You will then measure 240V from this neutral to the hot leg coming from ckt. 27 to the GFCI.

 

[hr3]

In your diagram at the switched outlet location your showing that the neutrals from both circuits 26 and 27 are tied together,, do both hots also go into this outlet??
You also show 2 outlets in the bathroom...correct,, if so the I would just install 2 gfi's in the bath all wired to the line side and be done with it.. that is as long as you haven't changed anything else as you took the switches and outlets out ???

 

[farmer2009]

Does both the circuits enter the box at the switched receptical? If so start looking there. Sounds like the two circuits are tied together some where by accident.

 

[GPintheMitten]

Good explanation on multiple path for neutral causing the gfci to trip.

I agree to check the wiring in the switched receptacle.

Here's what I would do
Eliminate the connection from bath to MB switch.
Feed the receptacle, switch and closet from circuit 26.

Of course the hot will need to be spliced by connecting 3 hots together, one from the circuit breaker 26, one for continuing circuit tto closet, and one to the switch. The white from the switch the gets wired to the hot on the duplex receptical.paint this white BLACK. Then the neutral from the distribution panel gets wired to the neutral on the duplex.

My guess is that someone tied all the whites together in the switched receptacle.

 

[Coyote machine]

Shared neutrals in MBR switched receptacle. Can't share 2 breakers neutrals, each needs to remain with it's own breaker. Maybe a good place to dedicate to your range?:laughing: