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Is it safe to work on a light with the light switch off but the breaker on?

Is it safe to work on a light with the light switch off but the breaker on?

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Old 02-06-11, 07:24 AM
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Is it safe to work on a light with the light switch off but the breaker on?

Ok, I try to be a handyman. I do some minor electrical when necessary. A few weeks ago, I pulled a tile in our ceiling up and noticed whoever lived in our house before had two bare wires exposed for a light. Figuring that wasn't too safe if those touched, I wrapped both wires in electrical tape. Afterwords, I was wondering how safe what I did was. When I was working on the wires, I touched the bare wires. I just made sure the light was off though. But afterwords, I'm wondering how safe that was. AC wires have the positive white wire, the negative black wire, and the ground wire. The positive white wire is the switched wire. But, seeing it's AC (alternating current), why didn't I get electrocuted when I touched the black wire? Doesn't alternating current mean that 50% of the time, the black wire has a positive 120v and it's constantly alternating between the black and white wire?

I figured before I hit submit on this forum, I should google it real quick. I found this article...

HowStuffWorks "Direct Current vs. Alternating Current"

The power that comes from a power plant, on the other hand, is called alternating current (AC). The direction of the current reverses, or alternates, 60 times per second (in the U.S.) or 50 times per second (in Europe, for example). The power that is available at a wall socket in the United States is 120-volt, 60-cycle AC power.
So, why didn't I get electrocuted when I touched the black wire?
 
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Old 02-06-11, 07:37 AM
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The terms positive and negative are not used in reference to AC power. You have ungrounded hot, grounded neutrals and grounding conductors.

The white should not be switched. A re-identified white can be part of a switch loop.

You individual conductors that you taped up should be replaced with a proper cable.

It is never safe to assume a switch will kill all the power in a box. It is recommended to turn the breaker off.

The reversal is in reference to the sine wave shape of the AC power.
 
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Old 02-06-11, 08:12 AM
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Ok, I was assuming the white was the switched... More I think about it when I see a bunch of switches, the white all go into a wire cap and the black is switched... So, I'm guessing it's the black that is switched then. I didn't confirm that at all.
 
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Old 02-06-11, 02:11 PM
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.... also occasionally you'll find a light that is powered at the light and not at the switch - that could make for a nasty surprise with the breaker still on
 
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Old 02-07-11, 07:57 AM
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Turn the breaker off, the switch is not to be trusted
 
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Old 02-07-11, 01:37 PM
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A young fellow I have known for several years got a surprise when he decided to do that at a local hotel....The switch was a "lighted" handle switch and those bleed 50 volts plus when off. Surprise!!! You just never know...plus I have seen certain mfrs cheapo switches just not work right from time to time.
 
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Old 02-09-11, 09:34 PM
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I can top Jim's story. Was changing a bulb in an ungrounded fluorescent fixture. Turned the switch off, unplugged the bulb, and got a shock strong enough to blow a 20A breaker. Turns out that the switch was wired in the neutral, not the hot, so the hot wire was still live. And the fixture not being grounded? Well, this old building has an abandoned gas lighting system. The fixture was attached to the old gas pipe. And down in the basement, when they needed to ground the panel to a large buried piece of metal, they used... the abandoned gas piping. Zap!

Moral of the story: It's always safer to turn off the breaker.
 
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