ECN Forum Forums General Topics of the Trade General Discussion Area US ELECTRICS

Hi i am curious if a workshop in the us has a 277/480 volt supply is the 120 volt supply for office and other equipment derived from a seperate pole xformer or from a xformer in the building thanks from annemarie

Usual practice is a customer owned transformer to step down 480 to 120/208 volt.

There are instances where there are multiple utility services with different voltage characteristics, but the most common are customer owned transformers

Annemarie, I have installed the electrical systems for a number of commercial and light industrial buildings.

The usual method is for the power company to provice 480 volt "three phase" power, with a neutral - so it's 277v. from any 'hot' wire to the neutral, and 480v between any two 'hot' lines.

A customer-owned ('customer' being the building owner, and not the tenant paying the electric bill) transformer will be installed to supply a panel with 208v/120v three phase power.

Any line-to-neutral circuit is single phase.

Often there will be a 480v panel set next to the 208v panel. 277v circuits are often drawn from the 480v panel for the permanent lighting. Most of your machine loads will also come from the 480v panel.

The 208/120 panel is usually filled with just 120v circuits. An exception might be the air conditioning; those guys never order the right (480v) stuff.

This is the usual, and preferred, practice. There are plenty of exceptions, usually found in older areas.

Thanks for your reply they are both very informative im glad i found this site thanks all Annemarie

And just for reference in Canada we usually use 600/347 instead of 480/277 volts.