Delta transformers

[Chong]

I was taught that if you have a 3 phase ,Delta connected, overhead service, that if the power company uses three transformers up on their pole then 1 of the 3 transformers will be larger than the other 2. Reason being is that the larger transformer will be carrying all of the 120V neutral current, and the 2 other transformers don't carry any neutral current. I was at a job yesterday where the panel had a 208V high leg, and when I looked outside up on the pole all 3 transformers were the exact same size which I thought meant that the service would be a 3 phase Y connected service. Can you have 3 transformers the same size and still connect them for a delta service?

[charlie]

Look at my answer in this thread (http://www.mikeholt.com/codeforum/ultimatebb.php?ubb=get_topic;f=3;t=001543). Can you have 3 transformers the same size and still connect them for a delta service?Yes, it is done all the time. If most of the load is 3Ø, there is no need for a larger transformer for the 1Ø load. :D

[Chong]

Thank you very much. I will admit that I sometimes would drive up to a building and look up at the transformers before I went inside and if I saw 3 equal sized xfmr's I would be thinking I had a Y connected service and no 208V high leg. Now I know that I must always use my tester to verify the voltage. ;)

[charlie]

Generally speaking, an electric utility will install a "ring bus" around the three transformers to pick up the neutral connections on a wye bank and then have only one conductor going down for the neutral. If the electric utility in your area uses that method, it is easy to tell the difference between a delta and a wye bank at a glance. :D