Replacing a light fixture - switch off, still hot

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Old 01-04-10, 06:47 PM
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Replacing a light fixture - switch off, still hot

A few months ago, I replaced a small ceiling light fixture in a bedroom in my home. Light is powered from the source to the fixture, then controlled by a switch that is dedicated to the fixture. I can't remember if the power continues on to another fixture or terminates at this light, and don't feel like checking. (I'm asking because I was recently reminded of the incident and was curious.)

I turned the switch off, which logically would leave the fixture powerless and safe to work on without much caution, and proceeded with the replacement. At some point, I touched a black wire and got a bit of a shock, which came as a bit of a shock since I believed that all power was off to the fixture.

I've come up with one theory as to why this would be the case, and it relies on there being another fixture further down the line (therefore remaining powered whether or not the switch in this bedroom was on), but I can't remember if this is the case. I didn't touch either of the source wires together or at the same time, etc. I believe I only touched the hot wire itself, as it was at a splice and I was replacing a cap.

Is there another reason for this? I know now to watch out for it and that turning off a light switch isn't the same as killing the power, but I wanted to know what was up.

For the record, I get it. Hire a professional. However, I am fairly experienced in construction and know enough to know when I need to hire a licensed electrician. I have two in my family that I use for anything major. I am not of the opinion that they should be called when changing a light fixture, a switch, an outlet, or things of that nature, provided you use proper cautions. And I can handle a buzz from 120 when I don't.
 

Last edited by moliphant; 01-04-10 at 06:57 PM. Reason: clarity
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Old 01-04-10, 07:40 PM
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Originally Posted by moliphant View Post
Light is powered from the source to the fixture, then controlled by a switch that is dedicated to the fixture.
This means there is power at the fixture box as long as the breaker is on, regardless of the position of the switch.

Turning the switch off is never adequate protection when working on a circuit. You must disconnect the breaker or fuse on the circuit before performing any work. Even then, a tester should be used to confirm power is off at the box. You also can't be sure the previous guy wired it up right -- perhaps the breaker you thought would work didn't fully de-energize the box.

For the record, I get it. Hire a professional.
That is not necessary for replacement of a light fixture, but it is important to learn electrical safety before DIY. A cheap non-contact voltage tester is very helpful to double-check power is off before reaching into a box.

And I can handle a buzz from 120 when I don't.
Electric shock is not like a physical hit which you can resist by being tough. Any shock has the potential to be fatal if the current travels through the heart muscle. The most common voltage for electrical deaths in the USA is 120V, even including commercial facilities which operate into the thousands of volts.
 
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Old 01-04-10, 09:08 PM
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Thanks for the quick reply.

Point taken on the last two quotes, I think I was being a bit glib and do recognize both the need for proper preparations and the potential dangers of electricity when the right steps aren't followed, but also that its not something that an educated homeowner can't handle.

As for the first, I posted the question here after a friend asked me about the same situation, and I didn't have a good answer for him.

Mainly, do you think that the fixtures were wired incorrectly or is it common for a fixture to still be live even though the room switch is off? I will always assume it is, from here on out, but is that usually the case? It seems like for the circuit to be live, the light would be on, since there doesn't appear to be any sort of bypass and the circuit should be broken at the switch. I'm just not sure there isn't something I am missing.
 
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Old 01-05-10, 09:00 AM
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Originally Posted by moliphant View Post
Mainly, do you think that the fixtures were wired incorrectly or is it common for a fixture to still be live even though the room switch is off?
There are a couple ways that lighting circuits are typically wired, which puts live power either at one of the switches or at the light fixture. Sometimes it could be both. Neither is right or wrong, just up to the preference of the electrician when the house is wired.
 
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Old 01-11-10, 07:30 PM
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Talking Switched neutral

Hi....sounds like the electrician did something common in older house wiring. They used the wall toggle switch to switch the neutral (return) wire. Instead of bringing the hot leg to the switch and bringing a switchleg back up to control the fixture, he left the hot leg at the fixture location and switch controlled the neutral. And if one location is wired that way, the whole house probably is too, so be careful.
 
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Old 01-12-10, 09:12 AM
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Originally Posted by chrisrw_66 View Post
They used the wall toggle switch to switch the neutral (return) wire.
There is nothing in the OP that suggests a switched neutral. It is much more likely the power feed comes into the fixture box and a hot switch loop runs to the switch box.
 
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