279 volts at light switch?

For reasons I don't want to explain, I tried to replace the light switch at work (in my office) myself. It controls two fluorescent fixtures.
Before taking the switch out I tried to measure voltages. Of course there was no neutral wire; however, between live and ground there was 279 vac (same reading with 2 different voltmeters; one of them also measured frequency, it was 60Hz).
So of course I closed it back up without trying to replace anything.
Why should there be 279v between live and ground? I should make clear that the switch was off, so as far as I know I was not measuring anything related to the coils in the fluorescent fixture.
All help appreciated.
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You are on the line to neutral leg of a 480v wye. (277v). That is a common way to wire lights in an office building. I bet the wires are violet and grey.
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On 05 Aug 2004 04:29:27 GMT, snipped-for-privacy@aol.com (Greg) wrote:

What is with the violet and gray? Is that the color code used for this? Heck, I have used violet for 120V in the past when I got some cheap wire. Is that against the code to use violet on 120V?
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It is not a code violation.
Different areas and different contractors establish conventions. Red, black, and blue are typical 110v colors.
You should always test voltage in commercial wiring. When you see bright or "strange" colors (yellow and orange, here) it is time to really double check.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing . . . . DanG (remove the sevens) snipped-for-privacy@7cox.net
(Greg) wrote:

building. I bet the

for
some
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No, that's fine. NEC makes the following requirements:
Ground: bare, green, or green with yellow stripe(s) Neutral: white or gray Hot: anything except the above colors
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It is not code but the unofficial convention is you use red and black for single phase 240v. Red, black and blue for 208 wye or 240 delta. 480 wye is brown orange and yellow with line to neutral (lighting) loads on violet (hot) and grey neutrals. It is so common that the NEC changed the wording of the color of neutral from "natural grey" (the color of old undyed rubber insulation) to just "grey". Prior to that it was a technical violation but it was tolerated because neutrals of 480v wye were worth distingushing from the 120v neutrals.
There is no "legal" requirement to do this but it is common enough that AFC makes MC cable armor in these colors for the trade.
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snipped-for-privacy@nospam.com wrote:

There's code and there's best practice. In fact, code is usually just best practices that are important enough to make into "law". (dealing with a contractor who's working on developing new codes for issues we keep seeing near where I live).
wire color is a best practice that I know of. Nobody would rely on it 100% but it makes work fast if you suspect that the green wire is ground (say).
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This is Turtle.
Most commercial lighting fixture are 277 volt service for them. Nothing new just the way it is.
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Yea the reason is you're committing a crime working on office building wiring w/o a license.

I should make clear that

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HA HA Budys Here wrote:

A crime.
There's some federal law saying who can work on an office? Sure, you might get your union pissed at you. Perhaps even violate a contract.
"What're you in for?" Changing a light switch. You? "I killed 7 guys. And installed a dimmer."
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wrote:

Yep, a crime.

Probably no Federal law, but it's very likely there are state laws and/or local ordinances mandating that *all* electrical work in commercial buildings *must* be performed by, or under the direct supervision of, a licensed electrician.
Clearly the OP is not a licensed electrician, else he would have known that 277V systems are common in commercial installations.
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buildings
that
Maybe, maybe not. Depends on the state. I can do any wiring or pipe fitting I want (in accordance with codes), but if I hire someone to do it for me, they must have proper licensing. It will vary by state.We are in a three state area and the states do not recognize the other state licenses. That probably has more to do with collecting fees than the skill of the tradesman. Ed
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Yes it's a crime. You can usually do wiring in your own home, because basically, if you mess up real bad it's you or your family who will suffer.
If you mess up in a commercial building you could cause harm to people who have an expectation of professionalism, and are PAYING for it.
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Be careful! That is the phase to neutral voltage common in commercial/industrial buildings. It is the same way in our building. ~277 is common for lighting loads.
Reminds of the time a lighting guy was out changing ballasts. He popped two 120volt ones before he realized the system was 277. John

at
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