86 volts between neutral and the electrical box?

Question

Context: I'm swapping out a dual electrical outlet in my kitchen with a combination switch/electrical outlet. I want the switch to control two small LED lights in adding to the room and the outlet to supply power independently.

I turn off the power, remove the cover. I see that there are two black wires in the back of the box attached together via a wire nut, not attached to the outlet.

A red wire on the hot/brass screw.

Two white wires on the silver screws.

No ground wire. I want to add one in, or a GFCI outlet at least. The house is probably fifty years old, give or take. So I go to check if my box is grounded with the multimeter, to see if I have 120 volts from the red wire to the box. I flip the breaker back on and check. I remove the wiring from the outlet.

I have 120 volts on the red wire to the box. I check the other wires just to see.

I have 0 volts on one neutral to the box. The second neutral has 86 volts to the box.

The question: I've done a few lights here and there but I haven't encountered something like this, with a neutral carrying voltage. Could someone shed some light on this? I feel like I should call an electrician to have a look since, this feels all wrong. But having said that...

Additional context: No prior issues on that outlet whatsoever. Nothing out of the ordinary. We only run a coffee maker off that outlet, maybe a cell phone charger sometimes too. It has its own 15A breaker. The only other comment I can make is that it seemed like the stairway light leading up to the second floor went off with the coffeemaker breaker... But later on the light seemed to be functioning still with the breaker off. I may have imagined this, but I felt like I should share for the sake of completeness. I have not been able to replicate that, the stairway light being affected by the coffeemaker breaker.

Thanks.

Answer 1

The 86 volts is likely phantom voltage. Only one of those wires is "neutral to the panel". The other is "neutral when connected to the other neutral via the receptacle, but floating when by itself". So that does not sound like a real problem.

Ground may not be a real issue. If you have metal conduit (doubtful, but tell us if you do) then that is your ground. If you have non-metallic cable (a.k.a. Romex) and you have metal boxes then the ground wires from the cables should be connected to your metal boxes, and the receptacles (if they are not bottom-of-the-line) can ground through their metal yokes to the box and all is good.

GFCI is important! You don't have to retrofit GFCI just because you do other stuff. But it is a really important safety enhancement, and you should seriously consider adding it (by replacing the regular receptacle with a GFCI receptacle) but the wiring then gets slightly more complicated.

However, you do have some potential problems here. Wire colors don't necessarily mean much, but the number of wires does. It appears that you have:

• One cable with black/red/white
• One cable with black/white

Normally on a "power an unswitched receptacle and pass through to another device" situation, you only have 2 wires (not counting grounds) in each cable. One definite possibility here is:

• Black/red/white cable brings power from two breakers
• Red and white go to the receptacle and white chains on to the next location
• Black passes through to the next location

This is called a Multi-Wire Branch Circuit, or MWBC. This saves some wire and can make sense in certain scenarios. However, it can result in some real complications with GFCI unless wired properly, the two breakers are supposed to be next to each other and connected (double breaker or two single breakers with a handle tie) and the neutral must stay connected for one half when the other half is being worked on.

I suspect an improperly configured MWBC may be at work here:

• Black/red/white to two separate breakers. You can check this out by seeing if there is a red wire going to the breaker you turned off for this receptacle. If so, find where the black wire from the same cable goes. Upload a picture of the panel showing these wires/cable if you can.
• Red/white (of black/red/white) goes to the receptacle. That is a problem because that means if the white wire is disconnected from the receptacle then you have disconnected the neutral of the other half (black/white) of the circuit. Which could do things like make your stairway lights not work temporarily.
• Black/white goes to the second location (stairway lights?) which means that if you turn off the kitchen breaker but don't turn off the stairway light breaker, current will flow through the neutral part of the receptacle you are working on if someone turns on the stairway light.

If my hunch is correct:

• You need to rearrange breakers so that the two breakers are side-by-side and install a handle tie. That may be trivial (they might already be side-by-side), might be minimal work (ordinary breakers that can be moved) or may be nearly impossible (tandem breakers that need significant rearranging). The breakers can not be two of a tandem pair - you should have ~ 240V between the black and the red.
• The whites must be pig-tailed - wire nut together the two existing whites plus a third short white wire between the other two and one of the receptacle neutral screws.
• Any time (this is what the handle tie is for) you do any work on this circuit, you turn off both breakers for safety.

Once this is resolved (and it could be something else, I am guessing MWBC), then you can look at (a) GFCI (which is really important in a kitchen) and (b) the original switched light plan.