House wiring question for the pros

Last night I was fixing an electrical box connection and I touched the wires that came off the switch for the lights downstairs. The switch was off, but for some reason I got a small shock when I touched the box (which is Earth grounded) and the wire.

I measured the wire to the box (Earth ground) and read approx. 16VAC. Someone told me this is normal for switches to "leak" a little bit of juice when in the off position.

It seems a bit strange to me, but can someone tell me if this is true and/or what this would be called so I can look up the explaination myself?

Thanks in advance!

Reply to
Peter
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Switches don't leak and even if they did, certainly not enough to produce 16 volts. Without more info, it's difficult to diagnose...

But, I would check for an open or high-resistance neutral (Which could very well put out 16 VAC between certain points).

The neutral wires (any of the white wires) should read close to zero volts between neutral and ground. Your grounding system could also be bad (high resistance at any number of points, or the fault could line in the transformer connections that serve your house.

See if you can get a utility professional or a licensed electrician to take a look at it. This could be a dangerous situation.

Beachcomber

Reply to
Beachcomber

If you have....

HOT------------+ |

Reply to
Michael

If you are measuring the voltage with a modern digital meter another possibility is that you are measuring a voltage derived from capacitive currents between wires or possibly across the switch. If the wire was connected to a good light bulb you probably have a problem, as in other posts. If the wire came from the switch with bulb not connected the high resistance of the meter may have allowed you to measure capacitive currents. Old analog meters are a lot more reliable for this kind of measurement because they have a lower resistance.

You could also make sure a good light bulb is in the circuit and measure from the switched off hot side the bulb to ground which should measure the neutral to ground voltage which could be up to a couple volts if the circuit is loaded.

bud--

Reply to
Bud--

Bud-- wrote in news:3e6b6$438dd51c$4213eb90$23843 @DIALUPUSA.NET:

Thanks for everyones input. I enjoy chatting about electronics and different things with people because I learn so much. Usually you can learn a few things from school or books, but when it comes to the real world, you can't beat it because you come across every day problems.

As far as the house wiring goes, I've asked numerous people and got numerous answers. Most answers were that something is wrong. Another person said 'old switches' sometimes develop corrosion and cause voltage to 'leak'.

In either case, this suggestion about the meter is interesting and I may try it. I wasn't sure if this occurance has a name associated with it or if it's a problem.

Reply to
Peter

Please keep in mind that if, in fact, you do have a leak, that is the same as an electrical resistance in the circuit. The power developed across this resistor will depend on the resistance in ohms of the material, and also on the SQUARE of the current. Too much current over a certain threshold and the device will just keep heating up and eventually explode.

I have seen this happen to cheap receptacle outlets that deteriorated over a period of hours to days. It is easy for this to start a fire. That's why U.L. standards exist for plugs, cords, switches, etc.

Beachcomber

Reply to
Beachcomber

It (the erroneous voltage reading) is a very common occurrance. People think they can use a digital meter on their household circuits, and trust the readings taken. It may be the most common mistake made by those unfamiliar with house wiring who use a meter.

When measuring voltage on 120 VAC branch circuits, use a 60 or

100 watt test lamp in parallel with the meter leads and you won't get erroneous readings. Until you have a known correct measurement, any answers based on that 16 volt reading are speculation.

Ed

Reply to
ehsjr

What Country?

Makes a big difference..

KJ.

Reply to
Kirk Johnson

You did not specifically state where you measured from to measure 16 volts on the box. Yes leakage always exists. But if that leakage created 16 VAC, then you have dangerous (excessive) leakage. Two volts with something else running on the same circuit. little to worry about. 16 volts in most cases - excessive - in any country. But again, what specifically and exactly were the two meter leads connected to?

How to weed out wr> Thanks for everyones input. I enjoy chatting about electronics and

Reply to
w_tom

It all started because my father and I were in the attic doing some re- wiring and he warned me that he has seen voltage leak through the switch and not to touch the wire. During the gathering of wires, he accidently touched the wire coming off the switch that is suppose to be dead because the switch is off and the metal box (which was Earth grounded). After touching both points, he got a shock and jumped back.

I thought this was strange, so I measured the wire that should not have anything on it to the box (which is Earth grounded) and saw 16VAC.

Tonight we tried removing bulbs in random rooms and found that when the bulb is in, we get mV AC (basically 0 volts), and when the bulb is out we get about 12VAC.

I'll accept that my digital meter is not meant for this purpose, but why the zap in the attic when accidently touching the wire to the Earth grounded box? For those who asked, I live in Massachusetes.

I was informed that the switch could be leaking and have a resistance of

10Mohms, the meter has a resistance of 1Mohms which we create a voltage divider thus reading 1/10 of 120VAC or 12VAC and when you add the bulb, it reduces the bottom half of the voltage divider to approx. 0 volts AC.
Reply to
Peter

But that's wrong. The only way the circuit is dead is if the circuit breaker is turned off. One wire to the switch is live, regardless of whether the switch is on or off, unless the breaker is off (or the fuse removed.) The metal box being grounded has absolutely nothing to do with whether a circuit is on or off. However, because the metal box is grounded, you can get a shock by touching it and a live wire at the same time.

After

As mentioned in an earlier post, in the absence of a known, valid measurement, speculation is all we can offer about the 16 volts you saw.

"removing bulbs in random rooms" and "when the bulb is in" --- um, which bulb is "the bulb"? Is it the bulb that is controlled by the switch in question, or does it have something to do with the bulbs removed in the random rooms?

The zap occurred because the circuit was not dead, as you erroneously thought.

For those who asked, I live in Massachusetes.

The numbers are wrong. A typical digital meter has an impedance of

10 megohms, not 1 megohm. To have your voltage divider ratio of 1/10, the leakage would have to be 100 megohms.

Lets assume there was a leakage of 100 megohms. How much current would flow? 120 volts divided by 100 megohms, or 120/100000000, which equals .0000012 amps - *way* too low to be felt as even the slightest tingle.

Forget the idea of "switch leakage". It is a non technical "fuzzy answer" and a meaningless phrase that tells you nothing. One of three things (or some combination of them) could put

16 volts on the wire you measured: a high resistance from a live wire, capacitive coupling or inductive pickup.

Your entire problem is based on incorrect procedure (circuit was not dead) and incorrect measurement (using a DMM on the circuit without ensuring it was loaded with a low impedance) and your problem understanding what is going on is exacerbated by incorrect data (the input impedance of the meter) and lack of familiarity with capacitive coupling and induced voltage.

The good that might come out of this in the future depends on you: *shut off the breaker* when working on your wiring.

Ed

Reply to
ehsjr

You guys are funny. I'll keep watching

Reply to
Michael

Now the important number. How much leakage? When that 12 or 16 volts exists, put the digital meter in AC current mode (start with highest setting or 2 amps, and work down). How much current? 1 ma or more suggests a problem. Again, current value from that open (no load) wire to metal box - a number - is when the definite answer exists. This done, in part, so that you leave this experience with useful knowledge.

Your digital meter is exactly for this purpose. When d> It all started because my father and I were in the attic doing some re-

Reply to
w_tom

It is perfectly normal for there to be a few volts difference between your earth and nuetral connections - 16v is normal if that is what you were measuring?

The nuetral would be connected to the switch via the lamp or fitting and the 16v would still be there despite your having turned off (what I assume) is the mains supply to the lighting circuit.

Reply to
Harry Bloomfield

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