Three phase panels?

Question

Can you tell if your transformer is a wye or delta by measuring the voltage at the panel? Or would you have to physically look at the transformer?

Philomel · Answer

Look at the transformer data plate !

oldschool · Answer

Anyone asking such a question hasn't cracked a book on three phase or AC power or transformers. There is a natural reluctance to help someone who refuses to help themselves.

qrk · Answer

For distribution, most commercial installations use wye which has a neutral/ground connection. This allows you to use the feed as 3-phase (commonly 208V for light commercial) and single-phase (120V which is derived from the 208 3-phase feed and neutral). You will read consistent voltages from each phase to neutral/ground.

Delta is usually not ground referenced, although there are odd installations that do have grounded delta connections (probably found in really old buildings). If you measure the voltage between each of the phases and ground, you'll probably get odd readings if you're using a high-impedance voltmeter. It's better to use an old analog meter for this measurement.

Three phase panels?

3 Answers