208 volt, half on half off

1705 Views 6 Replies 4 Participants Last post by Tom, May 20, 2008

Tom

Discussion Starter · May 19, 2008

I have noticed on occasion that some 208 volt ballasted lights in service station canopies are wired in such a way that only one of the two 120 volt conductors supplying power to each fixture is controlled by a time clock, while the other stays energized all the time. I wonder if this kind of wiring is intentional or just a mistake. If it is intentional, what is the rationale?

Thanks,
Tom

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Romexking

· #2 · May 19, 2008

Tom said:
I have noticed on occasion that some 208 volt ballasted lights in service station canopies are wired in such a way that only one of the two 120 volt conductors supplying power to each fixture is controlled by a time clock, while the other stays energized all the time. I wonder if this kind of wiring is intentional or just a mistake. If it is intentional, what is the rationale?

Thanks,
Tom

Oh it's intentional all right, but that doesn't mean it's a good installation. It is most likely done to save someone from purchasing a larger pole contactor. This way they only need 1/2 of the number of poles, and the lights still turn off. It's not what I would recommend, but I don't know of a code that it violates.

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480sparky

· #3 · May 19, 2008

Romexking said:
.... but I don't know of a code that it violates.

410.54(B).

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Romexking

· #4 · May 20, 2008

Well there you go...not a good practice and in violation of the NEC.

Thanks for the reference :thumbsup:

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Tom

Discussion Starter · #5 · May 20, 2008

Romexking said:
Well there you go...not a good practice and in violation of the NEC.

Thanks for the reference :thumbsup:

Thanks, all. I actually wondered if this kind of wiring mightn't be done just to save on contactors, but on second thought decided that was too silly an idea even to suggest. It goes to show that when changing ballasts you can't depend on the time clock override switch to shut their circuit off.

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randomkiller

· #6 · May 20, 2008

Tom said:
Thanks, all. I actually wondered if this kind of wiring mightn't be done just to save on contactors, but on second thought decided that was too silly an idea even to suggest. It goes to show that when changing ballasts you can't depend on the time clock override switch to shut their circuit off.

Well I would hope that before you went pulling off wires you would check to see if you had potential on them or not.

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Tom

Discussion Starter · #7 · May 20, 2008

randomkiller said:
Well I would hope that before you went pulling off wires you would check to see if you had potential on them or not.

I do...now.

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