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.
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)
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.
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).
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."
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
Clearly the OP is not a licensed electrician, else he would have known that
277V systems are common in commercial installations.
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
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.
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.
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