Electrical Question - Voltage Even when Switch is Off

I have a wall outlet controlled by a switch on the wall. Today I noticed that when the switch is on, the outlet reads 122VAC. When the switch is off, it reads 40-42VAC. Um…keeping in mind I’m going to call an electrician about it, is there a common problem that would cause about 1/3 voltage to appear at a wall outlet?

(FTR it’s a 2-prong ungrounded outlet)

As a follow-up question - I’ve just got the 2008 NEC book, all 1400 pages of it. I can’t find in there where it says that new wall outlets must be installed ground conductor-side up, even though I’ve had not one but two actual electricians gruffly tell me that “the electrical code requires it”. Can anyone point me to the chapter and verse?

I actualy had this one - it was a case of the switch installed on the neutral, and the fixture (exterior light) had shorted to ground - the hot line was connected reqardless or switch position, but when it was “on”, the return had a nice, spiffy route, when “off”, it had to rough it over the ground. Is there a ground either in the switch box, or is the outlet grounding in some creative manner?

Hm…as far as I can tell, there is no ground at either the switch or the outlet (it’s an old house, the circuits aren’t grounded except for a couple which have long, circuitous lines running to the plumbing). I’ll see if I can take a look when I get back home.

Is it by chance an illuminated switch or socket and somehow you are reading the voltage drop across the little tiny neon bulb?
Other than that the only two things I can think of are a defective breaker, or (and this one is a doozy) you have:
[li]You have a shared neutral[/li][li]another consumer upstream from the socket turned on (electrically further away from the panel)[/li][li]High resistance in the neutral leg between your socket and the electrical panel[/li][li]You were measuring between the neutral and ground[/li][/ul]
Then I could understand 42V on the neutral leg.

Other than that, I got nothin. We need Danceswithcats he is our resident electrician IIRC

No illumination LEDs, bulbs, or anything. As far as the other items…don’t know yet.

It’s a mystery alright. I wish I had a wiring diagram of the house.

Defective breaker I guess could be a possibility. I’m trying to replace my breaker box but can’t get any reliable electrician to give me the time of day. I should rant about that some time.

I’d like to see that, too. (You are referring to the ground conductor pin on a 3-prong socket, aren’t you?) I always thought the 3rd pin should be DOWN, as that’s the way I see it most of the time. Is the new style UP, and if so, why?

Wikipedia is not official code of course, but in the worldwide sockets page, it says:

Still, the picture shows the 3rd pin at the bottom.

Yes, that’s what I was referring to.

From what I can tell, the “it’s in the code” I was told was really the electrician saying “I just want to do it this way”, thinking Ms. Dumb Homeowner wouldn’t know nothin’ about no code. I also called my city and county and discovered there was nothing in the building codes either.

The number of times I’ve had someone say “it’s in the code” and it be wrong is astonishing.

Hmm…just noticed, we can’t edit our posts…anyhow, the ground-pin-up I’ve heard called the “Catholic safe” configuration. Because the urban legend goes that Catholics, leaning over to plug/unplug a socket, would somehow, against all logic, frequently get their rosary tangled up in it and electrocuted. And yet, I’ve had “master electricians” tell me this swearing they’ve “heard it happen so many times”. :rolleyes:

What sort of meter are you using? A DVM will have a high enough internal resistance to read a voltage due to inductance. An old analog voltmeter will not.

Regarding having the ground up vs. ground down, a lot of commercial electricians like to put the ground on top. If the ground is down and the plug works partly out of a socket, then a conductor that falls on the prongs could cause a direct short. On the other hand, a lot of customers are used to seeing a “face” on the plug and think that the other way is upside down.

It’s a digital voltmeter (volt, amp, capacitance…you name it) but it doesn’t have any problems with other outlets in the house - they read “0” or close to it when off.

More exploration has to wait until this weekend, where I will do testing and maybe, if it’s interesting enough, post pictures.

You have an open neutral somewhere in that circuit. Pretty much guarantee that.
Every time I find this phenomenon I can trace it to a loose or open neutral somewhere in the circuit. Every time.

I’m pretty sure there was a thread about this sometime back. I think the best logical explanation for this was: say you have metal covers, and a plug loosely plugged in, and the cover comes loose and falls onto the prongs of the plug. It would be better to rest against the ground prong instead of the other 2. I don’t recall if anyone was able to cite the code. (Now I’m thinking that someone said it was in some juristiction’s code book, but the book wasn’t online.)

Do a search for it.

Are you using a digital meter?

I just had my 2008 NEC continuing education class, and the trainer specifically said that’s not a code requirement. However, most of the class (all three of us) seemed more knowledgeable than he was …

A requirement like that is more likely to be in the UL listing, or in the UL standard for the device. In that case, the applicable UL standard is UL 498, Attachment Plugs and Receptacles. I’ve not read that one, but if someone’s interested, I can check.

Can I suggest that anyone with older homes (or even new) pick one of these up next time you are at the hardware store! I’ve used to countless times at work and home and it may help you here.


I also alway have one of these in my pocket :


I would put my money on this. Your meter doesn’t have enough impedance to drop all the voltage across it because the open circuit is also high impedance (the voltage divider rule causes the largest voltage drop to be across the largest resistance which is usually the meter). Strange looking voltage readings like that almost always wind up being traced back to a loose wire somewhere. Finding that wire might be tricky. Start with the switch and the receptacle and work your way out from there.

Or it could be caused by zombies.

Oops! :smack: