Hey, it won't shock me. OUCH!!!

Factual Questions
1

Recently, the wife, kids, and I moved into a new house (rented). As I was making the adjustments to the new place, I decided to change out a ceiling light fixture. I didn’t like the existing one and wanted to put in my own.

So, I checked to make sure the lightswitch controlling that light was off. Then, I climbed my trusty step ladder and disconnected the old light, leaving three bare wires (black, white, and ground). In installing the new light, one of the wires shocked me. Not enough to do damage, but it hurt, darn it. The light switch was definately off, and I touched to wires of my light fixture to the house wiring, and got no light.

To finish the job, I disconnected power at the braker box and installed my light in short order. After restoring power, the new light (and switch) works as expected.

My question is, what kind of wiring would still have power in the line even with the switch turned off? If there’s power, why doesn’t the light turn on? I’ve installed ceiling fans in several places in this house, and have not had similar experiences with the other utility boxes. It’s just this one. My reputation as an amateur home handyman is in your hands.

2

The ground wire is connected to a lot of electrical stuff & it can have surplus electricity. As a matter of fact, I got a shock a few times when taking a bath & touching a faucet. Well, you know guys, they wait a while before calling the gas comp. The gas comp came out in an hour [must be a record] & reground the house, pole, & electrical box because the ground was leaking, which is what you probably have.

3

It sounds like the switch may be wired incorrectly. I’m no expert but I think on a 2-wire houlsehold power, one is neutral (near ground) and the other has voltage (115V RMS). If you put a switch on either of the two, it will turn off the light. But if the switch is on the neutral wire, the voltage is still present with the switch off.

4

scr4’s description is correct. The switch is supposed to interrupt the hot wire. If it interrupts the neutral, you can still make a circuit betweeen hot and ground. This is almost certainly a code violation. You said you touched two wires to the light, but did you try all three combinations of two of the wires? If you did, and got no light, then you do have a grounding problem somewhere like Handy mentioned, and should have that checked out.

Either way, I’d be concerned about what other problems there might be in the wiring that you don’t know about. I’d suggest buying one of those little outlet testers, and checking out the outlets. you might have open grounds, or switched polarity on polarized outlets (wide vs narrow slots). This would tell you these things. (I think. I’ve never actually used one myself.)

5

I havent read the National Electrical Code lately, but I believe that it is ok to send the hot wire to the light first, and then send it to the switch. What this means is that turning off the switch does not kill the hot at the light. IIRC there has been much discussion on some of the home electrical newsgroups about this.

Any electricians out there?

6

[QUOTE

My question is, what kind of wiring would still have power in the line even with the switch turned off? If there’s power, why doesn’t the light turn on? **[/QUOTE]

Because you broke the power loop by turning off the switch. This means everything from the circut box to the break is sill hot.

let me try to draw it–
CIRCUT BOX–HOT WIRE----LIGHT JUNCTION BOX–HOT WIRE–LIGHT SWITCH OFF—DEAD WIRE—BACK TO CIRCUT BOX

7

according to my book the switch must interrupt the hot wire and not the white neutral wire so that installation does not meet the code

8

sailer, scr4, and ZenBeam are correct. You may be able to re-wire things to meet code, depending on what’s in the box at the switch. This would probably be a good thing to do, so the next person to come along and change the fixture doesn’t get electrocuted :slight_smile:

I agree that checking the receptacles with a tester would be a good thing also, given what you’ve seen so far. Or, you could spend $50 or so and have an electrician check it out. Either way, it’s pretty cheap if it keeps someone from being electrocuted some day …

Arjuna34

9

The question is, why didn’t Drum contact the owner of the house? It’s their job.

10

Being from the UK and an electrician by trade (ex-electrician these days) I’m interested in the differances between your electrical system and ours.
I pick up little bits from threads like these.

With our light switches it goes like this -

Main box to ceiling fitting mounting box.(Rose)

From the rose a wire is taken that leads down to the switch and back up to the rose.

The return wire from the switch is connected to the lamp pendant cable.

The other side of the lamp is the connected through the pendant cable to the neutral which goes back to the main box.

If you turn the lightswitch off there is still power on one side of it and there is still power to the ceiling rose.

To kill it you must remove the lighting circuit fuse.

UK domestic supplies(just for your own personal interest) -

We use 220v 50Hz - that is one phase of a 3 phase supply.
This is taken from a star connected 3phase district transformer(tx).
The neutral goes back to the star point of the tx.
An earth wire is usually taken from the same point or the neutral may be split into earth and neutral at the point of entry into the household.
The star point of the tx is physically connected to earth.

From what I can deduce you guys do not seem to run a separate earth wire.
In most appliances we use, the body of the equipment is connected to earth.
If a fault within the appliance should occur so that the casing might become live this current is discharged straight to ground and will result in the fuse going and hence disconnection.

11

Handy

The chances of surplus electricity, as you describe it, can only happen in pretty unusual circumstances as I read it.
The only way that the neutral could be live enough to give you a shock would be if there was a very heavy current load and the neutral wire had some resistance in it.(or mabe a complete break)
Then the neutral voltage would rise with respect to true earth.
To get a shock that voltage differance would have to be pretty substantial at least 25 volts.
You would have to be connected in some way to a true earth and the neutral at the same time.
A 25 volt shock is most unlikely to harm you but many of your appliances would either stop working or in the case of lights they would go dim.
Reason is that since neutral = 25 volts, say, then there would only be around 90 volts left between live and neutral.

Mind you I’m saying this from the other side of the pond and do not have the exact knowledge of your systems but I have worked on 110v ac systems on ships.

12

casdave,

I’m not an electrician, but I have read some of The NEC (National Electrical Code), along with the usual guidebooks. I’m an electronics tech by trade. Reading code has helped me a bit at work, along with rounding out my training as a Jack-of-All-Trades.

Households in the US run on 60 hertz, 110/220 volt, single phase power. Power comes off the pole as two 110V legs of opposite polarity with a common neutral; the transformer on the pole has a 220V secondary with a center tap for the neutral. The neutral is connected to ground (earth, of course) at the service (main breaker box). Ground has to be a rod driven into the ground or a clamp on a water pipe. There are additional requirements, and some cities no longer accept a water pipe ground. The ground connection to earth is made at the main service; no other connections are allowed.

After going through a main breaker (two 110V breakers with the levers tied together so that they trip together, probably the same as what you have), the two 110V legs are zigzagged down through the breaker box so that no two adjacent breakers use the same leg. This makes it easy to use the 220V breakers that are described above and assures that neither leg is overloaded (at least an electrician would have to try pretty hard to put all the breakers on the same leg.)

Most circuits coming out of the sevice have a hot wire (110V), a neutral which returns current to the box and the pole (still tied to ground at the main service) and a ground of the same size as the conductors which is also attached to ground at the main service. The separate earth wire is a somewhat recent addition to code, having been required in the last thirty years or so. All metal boxes must be properly grounded. I’m not sure whether the latest code requires a ground to all circuits, but since Romex, the common wire, has a black (hot), white (neutral) and bare (ground) conductor, I don’t know why anyone would want to do anything differently. On the other hand, most appliances are ungrounded, and two-wire polarized outlets do exist.

Ceiling boxes (I think you call this a rose) are usually wired the same way as you describe. The neutral is connected directly to the fixture. The hot is wired to the switch with a separate run of Romex. For the obvious safety reasons, all fixtures and switched outlets must be disconnected from the hot with the switch turned off; you cannot put the switch on the neutral side. I’ve also read the suggestion that, since the Romex has a white wire in it, you should wrap the ends of the white wire at the switch with black tape to indicate that it’s a hot. Alternately, you could have the white wire run the unswitched line to the switch box, since it’s attached to black wires at the ceiling box and switches are never on the neutral side. I don’t know whether code addresses this, though.

Alternately, the circuit can run through the switch box, with the neutrals tied together bypassing the switch. This isn’t as common, probably because it uses more wire.

FWIW, since the OP was about getting shocked with the breaker tripped, I have seen as much as 25 volts on a neutral when testing circuits with a high impedance meter, but it was probably capacitance between the hot and the neutral. I doubt that it would have had the current to shock me. Could a switch get dirty enough inside to pass a leakage current?

13

By the way, I’m not paid by the word. Really.

14

I’m going to agree with casdave on this one. The neutral wire runs through the house and completes the circuit back to the circuit breaker or fuse box. If the loads (fixtures) on that circuit aren’t distributed evenly, the neutral handles the excess current. Not having the loads distributed evenly isn’t necessarily a code violation, sometimes that’s just as even as the load can be divided. Considering the light switch breaks the circuit at the hot wire, your neutral is still free to carry excess current. And since you’ve just taken one load out of the design of the circuit, you may have caused the load imbalance that shocked you (pure speculation). The best way to do what you did would be to shut off the entire circuit at the fuse or breaker box.

This is of course, assuming the fixture didn’t have a switch loop in it, which temporarily uses the white wire as the hot wire (perfectly legal and up to code).

I would say there’s really nothing to worry about with your wiring and it is probably more common than you think. I have worked as an electrician for a few years in the states and been surprised by a small bite from the neutral wire when I wasn’t expecting it.

15

ZenBeam, if the tester you’re referring to is one of the ones that looks sort of like a plastic screwdriver that you stick into one hole of a socket, then yes, they will do all of the things you mention (they’re called inductive testers, btw.)
casdave, most of your other questions seem to have been answered, but I don’t think that anyone addressed the ground wire issue… I don’t think that they’re required, at least not on old construction, but they’re very common and increasingly standard. It is illegal to install a three-hole outlet (live, neutral, ground) if the ground isn’t actually hooked up to anything, and it’s a pain if you’ve got something with a three-prong cord and only a two-prong socket, so most electricians will install grounded outlets without even asking.

Oh, and welcome back, BratMan! I’m glad you haven’t given up on us; most of us really are nice folks. :slight_smile:

16

Ground wires may be left out of older buildings as part of a grandfather clause, but they are required in the US today. But the ground wire should not be the problem. If there is ever power running through the ground wire, that means somewhere else in the house, you have a short-to-ground and that should be found and addressed ASAP.

And labdude - no, you cannot run the hot wire to the fixture first. If you did this, with a neutral connected to the fixture, then the circuit is complete and the light would always be on no matter where you broke the hot wire afterwards.

handy - the ground wire shouldn’t be connected to any electrical stuff. Electricity wants to go to ground - that’s its goal. The ground wire is connected to the fixtures or junction boxes so if the hot or neutral comes loose and touches the metal fixture or junction box, then the electricity has somewhere to go then making that entire fixture a huge live wire. As I said above, if there is ever electricity going through your ground wire, something is loose somewhere.

17

That should read ". . . electricity has somewhere to go rather than making the fixture yada yada yada . . . "

18

Sounds like $50 to have an actual licensed electrician come in and check things out is a bargain(compared to your house/body being charred someday.

19

Interesting stuff,
I didn’t know that you used centre tapped secondaries but I can see the logic as a 110v zap is much less likely to kill than our 220v.

We use portable 110v centre tap transformers on higher risk applications(55v either side) such as professional portable power tools like for use on, say, construction sites.
This isolates the output from earth too.

Question for you, is the neutral wire a larger size than the hot wire.Seems to me it has to be as it carries the current from two legs? otherwise your loop impedance would go up.There is a post here that suggests that neutral carries only imbalance currents but as far as 110v goes I might be missing something.

As for high impedance testers well they can give false readings due to mutual induction of cabling so there are usually low impedance meters for power circuits with something in the order of 2k for 220v systems.(you can normally switch between differant impedances)

Our wiring colour code is rather differant and a Brit taking your stuff apart is likely to get a surprise.
Hot = red
Neutral = Black
Erath = Green/Yellow stripe

Appliances are
Brown=live
Blue=neutral
Yellow/green=earth.

Romex - is that similar to what we would call twin and earth, that is 2cores of equal csa and insulated and one bare core for earth all in a flattened casing and not very flexible, usually single core not strands?

20

OK, the following should apply to everything on this site, but…
PLEASE NOTE: DO NOT USE ANY OF THIS THREAD AS A CODEBOOK. DO NOT ATTEMPT ANY ELECTRICAL WORK IF YOU ARE NOT ALLOWED TO BY THE RELEVANT AUTHROITIES OR IF YOU DON’T UNDERSTAND HOME WIRING AND THE RELEVANT CODES. IF YOU ELECTROCUTE YOURSELF OR BURN DOWN YOUR HOUSE, ALL OF US WILL BE SORRY, BUT NONE OF US WILL BE LIABLE!
Well, it’s not like I’ve taken apart a line transformer…

Interesting indeed. I’ve never looked at the incoming power before; I’ve never worked on incoming power, and the utility company takes care of everything to the mast head. Having gone outside and looked, they seem to use the structural cable (what the two hots are wrapped around) as the neutral. On my 2 gauge 100A, this cable is a silver colored, stranded wire of about 1cm thickness. Wherever this wire terminates at an insulator (at the head, at a pole, etc.), short lengths of wire are clamped between one cable and the next. At the transformer, there are drops to what looks like three busses that the wires to which different houses attach.
I don’t know if it was obvious in my last post, but 220 within the house is made by having both hots go to an outlet. The neutral is also run and I think that it can be used to run 110 outlets on the same circuit. I’ve got an old book (not the codebook and not based on the latest code) that says that the neutral wire could be used as a ground on a 220V circuit, provided it was big enough. I think that the neutral is used for control circuits in heavy appliances. This way, you don’t have 220 running through, say, your dryer’s timer.

In the house, the neutral is the same size as the hot, as it carries the same electrons as the hot wire does for the lighting and small appliance circuits, and carries less current on the 220 circuits.
Yes, a Brit would be surprised inside a live circuit here if they were not forewarned:

British:[list=1]Hot = red
Neutral = Black
Earth = Green/Yellow stripe
[/list=1]
US:[list=1]Hot = black, (I think that red is used for the second hot in a 220 circuit, but I don’t know)
Neutral = White
Earth = Bare wire or Green. All ground screws are green.
[/list=1]

I don’t know if there is a standard code for appliances.
Twin and earth sounds like Romex to me. Its generic name is type NM (nonmetallic), but it’s usually called Romex, much in the same way that soft drinks are called Cokes.

Romex is always solid core. Since it is solid core and doesn’t have much physical protection, it is only used inside walls and unfinished attics. There are weatherproof types for outdoor/farm use or for burying deep in the ground.