480 delta 240 delta

[tshea]

I?m looking at a job that has a 480v 3Φ, 4w service. The job involves feeding a 480v 3Φ, 3w delta- 240v 3Φ, 3 wire delta transformer. Transformer is 75kVA.
My gut tells me the 240 needs to be grounded. Been looking all afternoon in NEC 2005 for answer. If not I can use standard 3 pole breakers, if so I can use ?H? breakers. H breakers are more expensive.
Can I (legally) install a 240v 3Φ, 3w panel. It will be SDS.

 

[augie47]

Re: 480 delta 240 delta

Not sure of your "H" terminolgy breakers.
If its a 240 delta system, corner grounded or ungrounded, you can not use a slash rated breaker (120/240) per 240-85.
Corner grounded or ungrounded is up to you.

Please note the requirements in 250-21 for fault indcators on ungrounded systems.

 

[jtester]

Re: 480 delta 240 delta

You are not required to ground the system, however you must use ground fault detectors as augie47 pointed out if you don't ground it.

Jim T

 

[jim dungar]

Re: 480 delta 240 delta

If you do ground a phase then you need to get breakers rated for use on "Grounded-B Phase" systems. For example, a Square D QO2xxH breaker is only rated for 5KAIC when used on a grounded phase system, but a QO3xx breaker is rated 10KAIC when used on an ungrounded system.