ECN Forum Forums General Topics of the Trade General Discussion Area Transformer

Good catch Don....

Dnk..

@ Don:
In Europe an ungrounded system like this would mandatorily need a permanent isolation control, alalrming at the first fault and switching off at the second? (similar even for 24 VDC btw in Germany)

Same for you?

Wolfgang

Correct and correct. A bad case of headarectumitis here with no excuses. I hope deverson solved his problem.

I think my first option is to try a 100 amp CB. I looked into a 125 but was told Cutler Hammer didn't offer one, plus the 100 amp was available next day. Both of the transformers megged fine and approx the same. I'll keep updates current. No pun intended!!!
Dave

Wolfgang raises an important issue. The secondary of this transformer is a separately derived systems, and must _either_ be grounded or meet the requirements for ungrounded systems.

But gaaaaaa. I can't find the code reference that requires ground fault detection on the ungrounded secondary. Am I imagining that ground fault detection is required? The closest that I can find is 250.21(3), which applies to control circuits only. (2002 code)

An an additional issue, the 480V secondary on this system is a pure 480V, not 480Y/277. You must use 480V breakers, not 480Y/277 breakers.

-Jon

The 480 volt secondary will only feed a 5 ton Liebert air conditioning unit. I have the secondary fused at 20 amps, well under what the transformer is capable of handling. I didn't included much info as it wasn't an issue as I couldn't get the transformer working let alone the Liebert.
Thanks
Dave Everson

Installed a 3 pole 100 amp breaker today and everything worked like a champ. I did notice a slight dimming of the lights when it fired up. It was fine after a second and everybody was happy.
Thanks for the help
Dave

Telsa's right
37.5 x 1000 = 37500 divided by 359.84 (1.73 x 208)= 104.21 amps primary.
37.5 x 1000 = 37500 divided by 830.4 (1.73 x 480) = 45.18 amps secondary.

Yoop:
Why did you revive this thread? Did I miss something?

No problem with it, just wondering. I see names that have not been around in a while!