277V lighting and 208V 3ph service

[champion]

Am curious and embarrassed to ask this question but I never have run into 277V lighting until just recently.
I would like to know how the 277v supply is derived for 277volt lighting.
I am assuming a 480v delta secondary high leg to grd could provide 277v for this purpose but the building I am about to work in has a 208v 3ph AC service.
Can someone assist my inquisitive venture into this 277V process.
Thank you in advance for any comments and
assistance.

 

[charlie b]

Re: 277V lighting and 208V 3ph service

A transformer with a 480 volt line-to-line WYE secondary will have 277 volts from line to neutral. Divide the two, and you will get that magical square root of three (1.732) number that shows up everywhere in three phase systems.

If the power coming into the building is 208 volts, then you have a problem. There are several ways to resolve it. But before I could offer advice, I would need to know more about the facility. One possible solution would be to install a step-up transformer to serve the lighting. Another is to use 208 volt lights. A third is to replace the service with a 480/277, and use a step-down transformer to get the 120, or 208, or 240 volts that you need for the rest of the building. It comes down to design choices.