# Home circuit reading 40V all of a sudden?

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• posted on March 8, 2010, 11:05 pm

In wrote:

I don't understand your description, but it's far from meeting code so you really do have something to be looked into. I still think you have an open ckt somewhere, either hot or neutral, depending on where you're seeing the 40Vac measurement. If one shows the 40V and not the other, that's going to be the one that is open ckted. Remember though if it's a switched outlet, the switch must be ON for the ac measurement. Another way to check the wires is to ohm them out. Kill the main power breakers and open the relevant breaker. and tie the hot to the neutral at one end or the other, and measure the ohms of the wires from the other end. It shouldn't be more than an ohm or two, often closer to a half ohm or so. Don't forget to disconnect hot from neutral when you're done. 120Vac hot to gnd = OK 0.0V neutral to gnd = OK assuming there IS a gnd wire connected. 120 Vac hot to neutral = OK.
Radio Shack sells handly little testers you just plug in and read the LEDs for this kind of thing too; handy to have.

Sounds like the vac just tripped whatever had to happen to push the ckt to an open ckt. Not unusual for loose wires in a fixture/outlet/switch/etc. They start with a surge that would create an arc if there were a poor connection and eventually the carbon from the arc would open the ckt. Happens all the time with loose connections.
HTH,
Twayne`
--
--
Newsgroups are great places to get assistance.

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<%-name%>
• posted on March 7, 2010, 3:23 pm

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.

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<%-name%>
• posted on March 7, 2010, 4:19 pm

I like the lamp idea. On it.

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<%-name%>
• posted on March 7, 2010, 5:05 pm

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).
Thanks for the help everyone.

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<%-name%>
• posted on March 7, 2010, 5:44 pm

Simple wasn't it ?
I am an electrician at a large plant, but I did not stay at a Holiday Inn.
I had something similar like that happen to me about 15 years ago. It took out the hot wire instead of the neutral. Vacuum cleaner did that to me also. Guess that motor starting up draws lots of current and will take out any marginal receptacle.
As far as the wiring question with the stove, I would not like to guess at that without seeing it. I don't think you will have any problems with it, but still do not like the idea of borrowing a ground with a wire of a much lesser gauge than the main wires. I don't know the code for the grounding, but bet it would not pass. As mentioned the old 3 wiring should be grandfathered in and would be ok. Most stoves will use the two 240 volt wires for the elements and very little current will be on the neutral wire, just whatever the stove uses for the 120 volts. Probably only the lights and clock/oven control circuits.

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<%-name%>
• posted on March 8, 2010, 12:59 am

..
Mike-
When you replace the receptacle, wire it up using the pigtail method.
The black from the "supply" and the black to downstream loads should be wire nutted together along with a short (pigtail) black wire that supplies the local receptacle. Do the same with the neutrals.
Wiring up a receptacle in this manner will keep the rest of the circuit working even if a "local" device fails.
cheers Bob

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<%-name%>
• posted on March 7, 2010, 3:37 pm
Mike Reed wrote:

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.)
--
bud--

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<%-name%>
• posted on March 7, 2010, 4:18 pm

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.

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<%-name%>
• posted on March 7, 2010, 1:46 am
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.
--
Christopher A. Young

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<%-name%>
• posted on March 7, 2010, 2:29 am
On Sat, 6 Mar 2010 12:47:52 -0800 (PST), Mike Reed

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.

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<%-name%>
• posted on March 7, 2010, 1:42 pm

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.

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<%-name%>
• posted on March 7, 2010, 4:56 pm
Mike,

Start at the source and work your way back.
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.
Good luck,
Anthony

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<%-name%>
• posted on March 8, 2010, 12:13 am
I would suggest two things. You have a bad neutral. Very bad and very dangerous, or you are using a sensitive digital meter that is picking up ghost voltage. As soon as you put a load on that kind of circuit, it will dorp to zero volts again. The first one you call the pro in. It might be in your home or it might be a problem out side.
If it is the second issue, it is nothing of substance.

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<%-name%>
• posted on March 8, 2010, 10:47 pm
In typed:

What you have is an open circuit in the Hot lead somewhere back to the breaker box, almost certain. The 40 Vac will often be a simply "phantom volage" caused by all kinds of things in the air and the high impedance of the meter can see it. Plug a nightlight or anything with a bulb into the ckt and the voltage will almost surely go away. It's sort of like static voltage, but comes from a different source by way of an analogy. 40Vac is a rather typical voltage for such things. If the 40V ac does not go away when a bulb is plugged in, there there is a serious wiring problem somewhere but 99.999% of the time it's going to be an open ckt in the wiring. Probably at an outlet or a switch. In fact, even properly wired ckts will often show the 40Vac if there is a switch to the outlet and it's turned off; same situation an an open ckt. But when the switch goes on, it should jump to a solid 120Vac level, whatever voltage is normal for your area.
It's may or may not be dangerous; it depends on where and how the open ckt has occurred. You should get it checked out soon, or open that breaker until someone does get there to look at it.
--
Regards,

Tom1

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<%-name%>
• posted on March 9, 2010, 12:11 am

======================================================================
This business of false or phantom voltage readings has been mentioned many, many times on this and other news groups in the past.
Even the cheapest of today's digital multimeters can pick up induced voltages from a 'dead' or disconnected wire which runs nearby other wires etc. A reading of 40 volts is probably meaningless. Another meter might give 21 volts; again meaningless! And even radio/wireless waves, which are very low strength higher frequency AC emanations can be picked up by any length of wire acting as an antenna/aerial!
As variuos posters have mentioned 'plug something 'real' such as a lamp, into the GFI and if it does not light up something is open somwhere between the output prong contacts of that outlet and circuit breaker feeding that circuit. Try the preceding outlet on that circuit to see if it it has power!
If all is correct back to the circuit breaker there should be full 115/120 volts on the live lead (usually black*) lead into the 'input' side of the GFI. However the neutral (usually white*) could be open.
*In North American practice.
Finally the GFI may be faulty. Pertinent ...................
Question; are any outlets 'upstream' of the GFI working OK?
Question; is the GFI the last outlet on that circuit 'run', that would mean there are no further outlets downstream of it!
Question; or is the GFI the first outlet on that circuit run; if so and it is faulty then all other outlets downstream of it may also have no voltage.
It is also very difficult explaining when one has no idea of the electrical knowledge of the enquirer! Something that, makes complete sense to anyone knowledgeable, may be difficult/dangerous to someone not so.

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<%-name%>
• posted on March 9, 2010, 12:21 am

Oops. Should hav read the following first .............................
Quote:

Unsafe by my reckoning, double ovens hooked to what gauge wiring?????? "using the oven's ground for the neutral ..............." yikes!!!! More than hokey by sound of it. And don't think an insurance company would be very sympathetic if something did happen!