480 Delta vs 480 Y

[jmd445]

I've recently acquired a building with two 34,500/ 480 volt services on a main panel board with a tie breaker.

The 1st service is from 3 individual transformers in a switch yard wired 34,500 Delta / 480 Delta with no neutral (service A).

The second service is from a pad mount transformer 34,500 Delta / 480/277-Y (service B).

Service A and B are interconnected with a 2000 amp tie breaker (this service dates back to the early '60's).

Obviously you can never close the tie should either service fail. I will either be removing the tie breaker or locking it out of service.

Recently there were some renovations and connected to the delta service were a main panel board with an electronic trip unit with ground fault protection and labeled 480/277 and an HVAC distribution panel board labeled 480/277 (this I?m not too concerned with since the HVAC is 480 3-wire, but, to say the least I need to re-label and identify the panels.

Finally to my question----service B is feeds three 3-conductor buss ducts. How can you pull a 480/277 lighting panels off a 3-conductor buss duct, shouldn't it be a 4-conductor buss duct, or are you relying on the buss duct case as your neutral/ground?

Thanks, Jim

 

[jtester]

Jim

Finally to my question----service B is feeds three 3-conductor buss ducts. How can you pull a 480/277 lighting panels off a 3-conductor buss duct, shouldn't it be a 4-conductor buss duct, or are you relying on the buss duct case as your neutral/ground?

You can't directly connect a 277/480 volt panel with single phase circuits to a 3 conductor circuit. It would be a code violation to use the case as a neutral.

Jim T

 

[don_resqcapt19]

Assuming that both transformers are fed from the same 34.5kV line, you also have a serious problem if the tie breaker is closed with both services energized.
Don

 

[tkb]

Re: 480 Delta vs 480 Y

Finally to my question----service B is feeds three 3-conductor buss ducts. How can you pull a 480/277 lighting panels off a 3-conductor buss duct, shouldn't it be a 4-conductor buss duct, or are you relying on the buss duct case as your neutral/ground?

You can't, but you could use a 480 delta to 480/277 wye transformer.

Tim