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Does a light switch cut all power to the light socket

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  • Jan 16th, 2012 3:30 am
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[OP]
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Jul 5, 2004
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Does a light switch cut all power to the light socket

I'm replacing a light fixture and I need to leave the breaker on. It's my understanding that flipping the light switch to off is the same as flipping the breaker, either way 100% of the power will be cut. The risk is that if someone was to flip the light switch accidentally, you could get a nasty shock, whereas nobody is going to bump into the breaker.

Is this right? Is there any way that if the light switch was installed incorrectly or if wires were run incorrectly that it wouldn't cut all power to the socket (the light switch works normally)?
16 replies
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Nov 12, 2006
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No, that's not reliable.

There are a couple of ways to wire the light/switch.

1. Power to the switch and then pass the switched power on to the light.
Your idea should theoretically be OK, if it were wired correctly.
Still, I wouldn't do it.

2. Power to the light box, and a loop to the switch.
Even with the switch off, there are live wires at the light.
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Dec 14, 2008
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Minden
arisk wrote: No, that's not reliable.

There are a couple of ways to wire the light/switch.

1. Power to the switch and then pass the switched power on to the light.
Your idea should theoretically be OK, if it were wired correctly.
Still, I wouldn't do it.

2. Power to the light box, and a loop to the switch.
Even with the switch off, there are live wires at the light.
You should be just fine with the light switch turned off. If the light switch is not in close proximity to the socket where you will be working, place a sign over it or tell family members to not touch it.

When you open up the light fixture, check the wires with a meter to ensure that there is no voltage present prior to diving in.
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Jan 19, 2011
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Shaner, please don't kill yourself! Your thinking is absolutely incorrect.

A light switch can be located on the "hot side/near side" of the light fixture it controls, or on the "neutral side/far side". Both installations are correct according to code.


In the first situation the switch turns off all electricity to the outlet, and you can safely work on your light.

In the second situation the switch does not turn off any power at the fixture itself, it only breaks the circuit AFTER the outlet box, but 120v ac is still hot in the box.

In both instances, turninng the switch off will turn the light off, making you think that power is cut to the outlet box, where in many instances, it is not.

In any event, I work with live 120 volt wiring all the time, and have never had an issue (except the one time I shorted out on my wedding ring, and the band heated up so much it burned my finger!) When working on wiring, if you aren't sure, just work on them as if they are live.

If you need help figuring this out, draw some simple wiring diagrams with hot and neutrals indicated, and switch in the two different positions.
"The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is."
Just a guy who dabbles in lots of stuff learning along the way. I do have opinions, and readily share them!
[OP]
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fieldhousehandyman wrote: Shaner, please don't kill yourself! Your thinking is absolutely incorrect.

A light switch can be located on the "hot side/near side" of the light fixture it controls, or on the "neutral side/far side". Both installations are correct according to code.


In the first situation the switch turns off all electricity to the outlet, and you can safely work on your light.

In the second situation the switch does not turn off any power at the fixture itself, it only breaks the circuit AFTER the outlet box, but 120v ac is still hot in the box.

In both instances, turninng the switch off will turn the light off, making you think that power is cut to the outlet box, where in many instances, it is not.

In any event, I work with live 120 volt wiring all the time, and have never had an issue (except the one time I shorted out on my wedding ring, and the band heated up so much it burned my finger!) When working on wiring, if you aren't sure, just work on them as if they are live.

If you need help figuring this out, draw some simple wiring diagrams with hot and neutrals indicated, and switch in the two different positions.

That's what I was worried about. So when working on live wiring, the idea is that if you touch one wire at a time you're fine, but if you touch both you could get a nasty shock? I know there's much more to it, but as long as I don't cross both wires I should be fine, correct?
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Jan 3, 2008
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W.GTA
Shaner wrote: That's what I was worried about. So when working on live wiring, the idea is that if you touch one wire at a time you're fine, but if you touch both you could get a nasty shock? I know there's much more to it, but as long as I don't cross both wires I should be fine, correct?

I second that, please don't kill yourself. Go kill the breaker and get yourself a tester. Your thinking is unsafe to yourself.
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Jan 19, 2011
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Shaner wrote: That's what I was worried about. So when working on live wiring, the idea is that if you touch one wire at a time you're fine, but if you touch both you could get a nasty shock? I know there's much more to it, but as long as I don't cross both wires I should be fine, correct?

That's more suitable.

So just to confirm, breaker kills power to the circuit completely, and makes all wiring in that circuit 'dead'. A switch on the other hand does nothing of the sort! A switch simply creates a gap in a conductor in the circuit, which only causes that specific portion of the conductor to be 'dead' that is located 'after' or on the far side of the switch. All conductors from the source (panel) leading up to the switch are still live!

Back to your issue, your thinking is correct. Many people work on wiring live, and the risk is minimal. The human body is not a particularly good conductor of current, unless it has bare feet on a wet floor. Touching two wires will give you a mild shock, not much more.

I can't recommend you try it yourself, as I would open myself up to liability, but I just replaced a switch hot, and zapped myself a couple of times.
"The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is."
Just a guy who dabbles in lots of stuff learning along the way. I do have opinions, and readily share them!
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Oct 25, 2003
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Even if you think your breaker is off, you should still be checking whether or not the wire is live or not with one of these anyways
Image
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Oct 25, 2003
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fieldhousehandyman wrote: That's more suitable.

So just to confirm, breaker kills power to the circuit completely, and makes all wiring in that circuit 'dead'. A switch on the other hand does nothing of the sort! A switch simply creates a gap in a conductor in the circuit, which only causes that specific portion of the conductor to be 'dead' that is located 'after' or on the far side of the switch. All conductors from the source (panel) leading up to the switch are still live!

Back to your issue, your thinking is correct. Many people work on wiring live, and the risk is minimal. The human body is not a particularly good conductor of current, unless it has bare feet on a wet floor. Touching two wires will give you a mild shock, not much more.

I can't recommend you try it yourself, as I would open myself up to liability, but I just replaced a switch hot, and zapped myself a couple of times.

Well, the reason you don't die when you touch the live wire is because electricity will find the path with least resistance, and luckily for you, it's probably in one finger, and out another finger.

If it happens to be in one hand and out another hand, it will no doubt travel across your heart :)
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Jan 19, 2011
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B0000rt wrote: Well, the reason you don't die when you touch the live wire is because electricity will find the path with least resistance, and luckily for you, it's probably in one finger, and out another finger.

If it happens to be in one hand and out another hand, it will no doubt travel across your heart :)
I have touched live to neutral wires with both fingers of same hand, and gotten a nice tingle, also done the same with a finger of one hand to a finger of another hand, and got the same tingle.

The across the heart is a bit of a myth, as I would have been dead long ago.

The way to properly kill yourself is to get it vertically through the body, and ensuring you are providing the least resistance possible by going barefoot on a wet basement floor.

In my personal experience, very little current travels fingertip to fingertip, same hand. or opposite.

The human body is not a particularly good conductor, especially when skin is relatively dry, the body is wearing rubber soled shoes or boots, and the like.

That does change a bit when it is fully wet in a cast iron tub filled with water, and it ispulling out the frayed cord of a clock radio, or working on live wiring barefoot on a damp concrete basement floor.
"The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is."
Just a guy who dabbles in lots of stuff learning along the way. I do have opinions, and readily share them!
[OP]
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Had one more question, my fixture box doesn't have the green ground screw in it. The hole for the ground screw is there, but not the screw. Can I just wrap the ground wires around the strap and then wire the ground wires together via a wire nut? Or do I have to go out and buy a ground screw? I mean as long as the ground wires are touching the metal box, a screw isn't really necessary is it?

If it is, can I use any screw, or does it really have to be a green ground screw?
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Jan 19, 2011
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According to code, the fixture and box should both be grounded to the ground conductor running back to the panel.

There should actually be two grounding screws in any box, octagonal, or rectangular, in an octagon box, look diagonally opposite.

That being said, ensuring the fixture is properly grounded by marretting its ground to the ground wire(s) entering the box is probably effective enough, but it would be nice to somehow get the box grounded as well.

look for another grounding screw in the box, or any other screw, even a screw used to mount the box, wrap a pigtail of ground around it, and away you go.

BTW is only one cable entering the box (comprised of a black, white, and ground/bare copper)? it is possible the ground is slipped under a grounding screw first, then the rest of it goes to the marrette

good to see your still alive!
"The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is."
Just a guy who dabbles in lots of stuff learning along the way. I do have opinions, and readily share them!
[OP]
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fieldhousehandyman wrote: According to code, the fixture and box should both be grounded to the ground conductor running back to the panel.

There should actually be two grounding screws in any box, octagonal, or rectangular, in an octagon box, look diagonally opposite.

That being said, ensuring the fixture is properly grounded by marretting its ground to the ground wire(s) entering the box is probably effective enough, but it would be nice to somehow get the box grounded as well.

look for another grounding screw in the box, or any other screw, even a screw used to mount the box, wrap a pigtail of ground around it, and away you go.

BTW is only one cable entering the box (comprised of a black, white, and neutral) it is possible the neutral is slipped under a grounding screw first, then the rest of it goes to the marrette

good to see your still alive!

Got it all figured out. The fixture is grounded and I just used a normal screw to ground the box. I'm sure electricity doesn't distinguish between the colour of the screw. Thanks for your help
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Dec 11, 2005
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fieldhousehandyman wrote: Shaner, please don't kill yourself! Your thinking is absolutely incorrect.

A light switch can be located on the "hot side/near side" of the light fixture it controls, or on the "neutral side/far side". Both installations are correct according to code.


In the first situation the switch turns off all electricity to the outlet, and you can safely work on your light.

In the second situation the switch does not turn off any power at the fixture itself, it only breaks the circuit AFTER the outlet box, but 120v ac is still hot in the box.

In both instances, turninng the switch off will turn the light off, making you think that power is cut to the outlet box, where in many instances, it is not.

In any event, I work with live 120 volt wiring all the time, and have never had an issue (except the one time I shorted out on my wedding ring, and the band heated up so much it burned my finger!) When working on wiring, if you aren't sure, just work on them as if they are live.

If you need help figuring this out, draw some simple wiring diagrams with hot and neutrals indicated, and switch in the two different positions.
100% correct, but t be even safer, you should always be checking using a voltage detector.

Flip the switch, check with a voltage detector. If it is good, you are OK. If not, flip the breaker, and STILL check with the voltage detector.

The moral of the story is, ALWAYS CHECK WITH A VOLTAGE DETECTOR BEFORE WORKING ON HOUSEHOLD WIRING!

You don't know what the last fool did in that box, flipping the breaker is actually no guarentee of ANYTHING, for all you know there is a second circuit in that box that has nothing to do with the light switch, heck maybe it is a 220v circuit to boot.

Voltage detectors are not expensive anymore, there is no excuse to not have one if you are doing electrical. The one I have I think cost like $15 tops, and it saved my bacon at least once.
To be nobody but yourself - in a world which is doing its best, night and day, to make you everybody else - means to fight the hardest battle which any human being can fight; and never stop fighting. -- E. E. Cummings
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Jul 26, 2010
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fieldhousehandyman wrote: According to code, the fixture and box should both be grounded to the ground conductor running back to the panel.

......

BTW is only one cable entering the box (comprised of a black, white, and neutral) it is possible the neutral is slipped under a grounding screw first, then the rest of it goes to the marrette

good to see your still alive!

???? don't you mean black, white and bare ground? with bare ground going under the screw? the white is generally called the neutral but , especially in switch/lights , it can be hot rather than neutral.
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Jan 19, 2011
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Yack!

mind fart, I meant black white and ground, or black white and bare wire.... oops going back to edit my post right now!

I think the OP figured out my mistake tho, or perhaps read my mind!
"The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is."
Just a guy who dabbles in lots of stuff learning along the way. I do have opinions, and readily share them!

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