Danimal

Hi fellas, hope you can help.
We`re bidding a service upgrade, existing is an 800a grounded "B" 480v delta. The owner, power company and county inspector don`t like the grounded B. Building was built and wired in 1960.
What should I be on the look out for if we go to a standard delta 480v system?
Will the existing 3-phase equipment need to be replaced, primarily motor loads. I realize I`ll be adding a neutral in many places, but will the three wire systems accept the new service?
35 years in the trades, licensed, experience in residential, commercial and some light industrial but no grounded B experience til now.
Thanks, Dan

InPhase277

Not liking a corner grounded delta is just showing ignorance on their part. It is a perfectly fine system, and in my opinion is safer than an ungrounded 480 V delta.

If you change the service to a 480 V delta, you won't be adding neutrals, because there won't be a neutral with the service. You will be adding ground detectors or a zig-zag grounding transformer. Also, some corner grounded systems didn't protect the grounded phase with an overcurrent device, so look at installing 3-phase panels where previously there may have been single phase panels, and 3-pole disconnects where previously there were 2-pole.

Likely, though, you are getting a 277/480 wye connected system, with a neutral. All the same things apply about circuit protection as far as number of poles.

There will be some good money involved either way. But if I were the customer, I'd hire an engineer to prove that a corner grounded system is perfectly legit, and try to convince the bonehead inspectors and POCO otherwise.

micromind

I agree completely. A corner-grounded 480 system is completely safe, and generally delivers more balanced voltage that a wye.

The only thing I could add is if there are 480 single phase loads (like transformers), they might need to be shifted around a bit to provide a better balance on the system.

People tend to be afraid of anything they don't understand, the sad part is their unwillingness to learn. I guess it's easier to make a demand or issue an order than it is to actually learn something.

Rob

Bob Badger

If you making the currently grounded B phase ungrounded you will need to look for incorrect / accidental bonding of this conductor to ground. Ring it out till it's clear.

Also if for some odd chance the original install used white as required for the grounded conductor you will need to somehow correct this to 'other than white or green'.

I also agree you may find single phase panels or two pole disconnecting means where you will need 3 phase equipment.

FWIW many engineers do not seem to like corner grounded 480 volt systems, I believe it has to do with stressing the insulation much more then 277 to ground. I could be wrong.

Danimal

Fellas, I`m not for changing service type here and you helped make the case to keep it.
Only one fourth of this service is for this building, the other 600a feeds quite a bit around the grounds. Chasing down and checking each piece of equipment will be exhausting and seemingly unnecessary.
I`m going to be meeting with the engineer in two days, I`m better prepared now and I thank you.
We have to replace all disconnects, panels, conduits and cable in this place, heat took care of that. Why make it any more wor than necessary?
Thanks again.
Dan

Bob Badger

Some more info here from Square D.

http://ecatalog.squared.com/pubs/Ele...2700DB0202.pdf

Richard Rowe

We have a 480 one phase grounded system here and when I first saw it I must admit I didn't like it. Once I spent a little time on wiring for it I saw that my dislike was for nought. We don't use it much now but have never had any trouble out of it and motors ran fine. When you first put your meter on Phase to ground and see that reading kind of makes you feel a bit uneasy.

Danimal

Guess my experience was the same, not sure what to think. Then the inspector and engineer didn`t like it, now what to think?
I`m learning though, and think it should stay.
Thank you, and the rest for your response.
Dan