[roboth]

I was attempting what I thought was a simple job in my kitchen (wired in ~1978), to add a GFCI to the first outlet in a chain of three outlets around my sink, and replace the worn out old outlets with new ones on the other two. From a process of elimination using the breakers (which aren't well labeled), I figured out that those three outlets were on the same breaker, and disconnecting the wires from what I'll call 'outlet 1' left the other two with no power when the power was turned back on. I figured it would be straighforward to put in a GFCI to protect the other outlets on the load side.

But here's where things got weird:

The original 'outlet 1' had a bare ground wire, a white wire that had a section of insulation stripped off which looped around the silver outlet screw and then went back into the wall, and red and a black wires connected to the two (connected) brass colored screws on the other side. So far, this seemed OK. I determined using my multimeter after disconnecting the outlet and while the breaker was closed again that the red wire was 'line' side (it had 120V to either neutral or ground) and the black wire was the 'load' side (no voltage between it and neutral or ground when disconnected from the outlet). The white 'neutral' wire also had no voltage to ground, as expected.

So... Here's where things got weird. I opened the breaker again, and thinking i'd cut of power from the circuit I figured the next step was to cut the 'continuous' neutral wire so I could connect it to the GFCI's 'line' and 'load' screws separately. But when i cut the wire, there was a spark and a different set of outlets went out! (i noticed because my work light went out).

Even weirder, I then double checked the now cut white wires with my multimeter, and now there was 120V to ground from one of them! Trying to figure out what was going on, I closed the breaker again, and found that between that 120V white wire and the red wire, there was now 240V!

What is going on here? Is something seriously messed up with this wiring?

My knowlege of home wiring is admittedly limited, but I figured this was going to be a pretty simple job... apparently not?

 

[Canbug]

Your counter receptacles are wired as a split receptacle. They are wired with a 3 wire. Bare copper as ground, white as neutral, black to one half of the plug, red to the other half. There is a little brass bar that has been broken off on the hot side of the plug so that it can be wired this way. It should be fed from a 2 pole 15A breaker. The receptacle should also leap frog the receptacle beside the first one. If you have 4 plugs, 1 and 3 are wired together, 2 and 4 are wired together. To install the gfci, will require a rewiring of the other plug tied into this cct.
It a lot harder to explain this in writing.
Disconnect all the wires. You should have 120v between white and black, 120v between white and red, 240v between black and red. Black and red are not line and load. If you only have one 3 wire in the box, it does not feed any other plugs. If you have two 3 wires, one wire is line and the other is load.
The GFCI will only work on 120v so you will have to cap off the red.

I hope I haven't confused you to much.

Tim.

 

[roboth]

Hi Canbug - i'm pretty sure that's not now this outlet was wired up. The red and black wires were connected (the tab connecting the two brass colored screws was still intact on the outlet) and there was 120V between the red wire and white, not between red and black. I got 240V between red and one of the white wires after I cut the 'continuous' white.

 

[Canbug]

Lets go back to square one. Do you only have 1 wire in the box? If you have two then you have in and out. Is the cct fed from a single pole or two pole breaker? You should not be able to get 240v from a white and a single colored wire. 240v is generally measured between black and red unless it is for a specific load like in a shop and you use a two wire. Then you will get 240v between white and black.
I'm not sure how or why the white wire loops back into the wall? Is there a chance you could post a picture?

Tim.

 

[roboth]

Hi Canbug - thanks. I will have to check some of those things when i get home tonight.

I did take a picture, but it's a bit of a rats nest of wires in there:

The yellow wire nut is re-joining the white wire that I snipped, and the orange nuts are just capping off the black and red wires while things are exposed and the power is back on.

 

[Canbug]

Thanks for the picture. Pull all your wires out nice and straight. Then we'll know what we're working with.

 

[Oso954]

He is working with a MWBC.
The easiest solution is to reinstall the receptacle and use a 2 pole GFCI breaker in the panel, assuming one is available for his particular panel.

 

[Luke M]

I'm not sure it's an multi wire circuit. It probably is, but it could also be a wiring error (cross connected neutral somewhere). I can't tell what's going on from the picture, too much is hidden.

No matter how it's wired, you can always use a receptacle GFCI; it's just that you might have to use one for every outlet, instead of one for the entire circuit.