Nov 20, 2022
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United States
Hi, I’m an electrician but needing a little help with understanding transformers. I’ve been asked by a friend to help with installing some lights in his hanger that run on 277/480. He has 240 at a panel that runs the rest of his hanger but I’m needing to step up the 240 just to run 5 lights. Is there a way to do this without investing in a pad mounted transformer?


May 15, 2021
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Well, firstly, I would inquire of the type of lights. If they are of the LED type, there is a good chance they will operate on the 240 you already have. Most electronic devices have "switch mode power supplies" that only require a portion of the incoming AC frequency, and they simply "crop" the part of the waveform they want, and flat-top the rest, hence "switching" pwr supply. This is heavier AC theory. Anyways, check your lights may not need to do anything. If unsure, connect one of them onto 240vac, see if they fire ON? Check their current as well.

Be mindful, if you "test connect" the light to a residential 240vac circuit (in your house), both line conductors (ungrounded) have potential to ground. Whereas, a 277vac system (from a commercial 277Y/480v 3Ø) has a grounded conductor (neutral). This may be of no consequence, but I'd just be mindful of it.

Failing that, check for either an autotransformer with 240-277 taps, or a "buck-boost" xfmr will do the same thing. "Pad mount" xfmr is WAY, you'd break the bank. You would need about 5kVA xfmr for qty=5 lights at an estimated 4.16amps @ 240v.

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