I plugged our vacuum in to the GFI in the kitchen, and when I turned it on, I heard a "pop" and assumed it was the GFI that needed to be reset for some reason. Well, the GFI plug was acting completely dead.
I pulled it out of the wall, pulled off the line wires and tested them bare.
40V?!?!?!
This circuit was fine this morning and has been installed for years. We recently remodeled and moved a couple plugs around, but they've been working fine for months (all on the GFI).
The breaker goes both directions with a positive click just like the rest. This all started with the vac switch. I turned around and used the vac on a different circuit with no problem.
The circuit to that outlet is most likely coming from another nearby kitchen outlet. Either it was wired through the "load" of the other outlets ground fault protection, or you have a loose connection at the location prior to the one with the dead outlet. The 40 volt reading means nothing
Plug a lamp into the outlet when you read the meter. If it really is 40V the neutral on your house has likely opened. The other leg of the 240V service will have 200V on it! This is obviously a very dangerous situation. Get it fixed FAST. Shut everything off in the meantime.
Check from the neutral wire at the outlet to the equipment ground. You should have near zero volts there. If not, the neutral is probably opened as someone else mentioned. The breaker might be bad even if it switches off and on like normal.
When one wire is close to another AC wire, there is some power that is transferred by magnetic waves. Your VOM is probably reading this "ghost voltage". There is probably not enough amperage to do anything useful. But, your VOM is very sensetive.
If you are seeing an induced voltage, you are probably using a digital meter, which are high impedeance, mabye 11MegOhms per volt.
You mght want to measure the same place with an analog meter. They are iirc 20KOhms or maybe 50KOhms per volt, either way must lower, so they put a load on the voltage that dissipates the 40 volts but very low maximum current that you may have, and the voltage will read correctly, probalby very near zero.
Analog meters are those with needles that move.
Except for FET-VOMs which are analog and use a needle, but have very high impedance. I'm not recommending one of those, but I think there have been none of those for sale for 25 years. And they probably say FET-VOM on them. At the bottom of the needle area, it says the impedance of the meter in ohms per volt.
For most things, I still like digital meters, which are auto-polarity for one thing.
I agree with the induced voltage concept. I have encountered this many times. Put a power strip onto your outlet, then put your voltmeter into the power strip. If you get 40 V, then plug some appliance into another receptacle in the power strip. Your voltage will go to 0. The most likely thing to be wrong here is that your GFI failed (a common occurrence). You can pull the GFI out of the box and measure the voltage going to the GFI. If you have proper voltage entering the GFI, then your GFI is dead. If you don't have voltage, then your breaker is probably bad. Either is fairly easy to replace.
Ok, I pulled out the receptacle and disconnected the line wires to test them the hot/neutral voltage is ~11V, probably the close-wire effect (mentioned elswhere) there.
Neutral/ground is zero, and hot/ground is 124V, just like working receptacles.
So now I guess I check to see if the breaker is bad? Obviously the breaker box poles would be ok since all the other circuits on that side are working fine, right?
Well, I guess it can't be a bad breaker if the hot is hot working...
So I have an open neutral probably?
I'm starting to suspect a modification made about two montsh ago to accommodate our new double ovens. We had 240 going into the box for the oven, with one hot 240. The new oven required a 4-wire connection with two 120V hots. The electrician used the oven circuit's ground for the neutral, the neutral for the 2nd 120, and borrowed ground from an adjacent 120V GFI receptacle. I think something's hokey with that arrangement or its implementation.
Strange this all started when I turned on the vac (which had worked fine on that circuit since the oven went in).
If you have a very low voltage from the hot to neutral and 124 volts form the hot to ground, I would look for an open neutral. If you cut the breaker off and check the resistance between the neutral and ground you may find that open. There should be a very low (almost zero) resistance between the two. One guess is there are several recepticals on that circuit and atleast one is between that one and the breaker box. Try finding all of them and plugging a lamp into both sockets, one at a time. Chances are you will find power on one socket and not the other. A jumper between the screws can burn out between the two.
The new oven could have been wired the same as the old one. Just use 3 wires. While it will work ok electrically, the 'borrowed' ground wire may not be heavy enough to carry a short circuit current, especially if the short is not a 100% short, but a low to medium resistance short. That could result in the 'borrowed' ground wire getting too hot over a long period of time. Probably the borrowed ground wire is 14 gauge and the wires going to the stove are much larger.
Voltages sound like an open neutral, best covered by RBM. I might test with something like a light bulb in a pigtail socket. If the neutral was open just H-G would light up.
Very slight chance a breaker is tripped and has to be turned off hard to reset.
Do you know which breaker is for that receptacle? (H-G voltage should disappear when turned off.)
Are any other receptacles dead? (Could be where neutral is open, or also downstream.)
Do you know of other receptacles on that breaker that are working? (They would also be candidates for where the neutral is open.)
I agree. Some range circuits used to be just hot-hot-neutral and the neutral was also used for the ground. New circuits need a ground, but the old connections are still explicitly grandfathered in the code. Picking up the ground elsewhere is not appropriate (and is a code violation). Also at least one wire size too small.
I doubt it is the direct cause of the problem now. (But digging around in the box may have loosened a different connection.)
The ground is borrowed from a 14g cluster (same nut), but is a much larger stranded wire going to the oven box. The ground that was converted to neutral is much larger than 14g and stranded as well. So this should be ok then?
Yep, I've ID'd the breaker, and some of the receptacles on that circuit are indeed working. I'll roll around and figure out if I can identify where the open neutral lies.
Remove the breaker panel and measure the voltage right on the breaker when it's on. If you don't get 110/120 volts there, the breaker is probably faulty. Replace it before moving on.
If you know the order the outlets are wired in, work your way along the circuit, testing at each outlet until you reach the end. Most likely you will read full voltage till you get past a certain outlet. Go back to the previous outlet, pull it out, and inspect it (with the power off, of course). I'm betting a connection has arced, come loose, or otherwise failed in one of the outlets.
If you don't know the wiring order, pull every outlet out one by one and inspect the wiring. If it were me, I would go ahead and replace every outlet in the room. Unless it's a very large room or multiple rooms are on the circuit, it shouldn't cost more than $20 to replace all the outlets. Cheap peace of mind, and you'll know you have good outlets for the coming years.
Also, if the outlets are wired "daisy chain" (incoming cable is wired to one side of the outlet, outgoing cable is wired to the other side), I recommend rewiring so the cables connect directly with a short pigtail running to the outlet in that box. That way, power runs directly from one box to the other, and not through an electrical outlet.
Oh, if any outlets have the spring loaded "stab" connections on the back, replace the outlet and make the connection on the screw terminals.
Finally, inspect the wiring where it enters and exits the box. I've never had a problem with plastic boxes, but metal boxes can cut into the cable or can be damaged if the clamp was overtightened.
So, going from the GFI outlet closest to the breaker (next room), it was the only one working. I pulled the receptacle from the next one and examined it. Loose wire in there with some black from a flash/ burn. I tightened it up, restored power, and everything works. I'm replacing the receptacle right now (same 20A type).
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