Phase conversion, step up xfmr and corner ground

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Frank44

Member
Location
Oakland CA
I have the following installation:

2-pole 240V breaker with two #2 AWG and one #6 AWG EGC feeding a Phase Perfect phase converter which requires a 125 AMP service and outputs 58A, 240V, 3 phase.


The phase converter supplies a 100A 240V distribution panel (no main breaker) with #4 AWG.


On the distribution panel there is one 3-pole 240V 30A breaker supplying a table saw, with a 30A 240V 3-pole non-fused disconnect ahead of the saw.

Also on the distribution panel there is an existing 3-pole 240V 60A breaker with #4 AWG supplying a 240 to 480V step up 30KVA transformer (delta-delta). The 480V output of the xfmr goes to a fused, 3-pole 480V disconnect and has one load, a shaper rated at 20 full load amps (it is soft start).


Only one piece of equipment will be used at a time.


Two questions:


1. Do I need main breaker on the 240V 3 phase distribution panel (i.e. on the load side of the phase converter)?


2. The 30KVA transformer does not have a corner, or ?B? ground. There are no ground indicating devices. I believe one or the other is required even if the output is hard-wired to a single load. Is the corner ground preferable? Should it go to H2? (xfmr is a step up).

Thank you.
 
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texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
Frank44 said:
I have the following installation:

2-pole 240V breaker with two #2 AWG and one #6 AWG EGC feeding a Phase Perfect phase converter which requires a 125 AMP service and outputs 58A, 240V, 3 phase.


The phase converter supplies a 100A 240V distribution panel (no main breaker) with #4 AWG.


On the distribution panel there is one 3-pole 240V 30A breaker supplying a table saw, with a 30A 240V 3-pole non-fused disconnect ahead of the saw.

Also on the distribution panel there is an existing 3-pole 240V 60A breaker with #4 AWG supplying a 240 to 480V step up 30KVA transformer (delta-delta). The 480V output of the xfmr goes to a fused, 3-pole 480V disconnect and has one load, a shaper rated at 20 full load amps (it is soft start).


Only one piece of equipment will be used at a time.


Two questions:


1. Do I need main breaker on the 240V 3 phase distribution panel (i.e. on the load side of the phase converter)?


2. The 30KVA transformer does not have a corner, or ?B? ground. There are no ground indicating devices. I believe one or the other is required even if the output is hard-wired to a single load. Is the corner ground preferable? Should it go to H2? (xfmr is a step up).

Thank you.
Click to expand...

1) Yes, you need a breaker per 408.36.
2) I agree. There are some downsides to both ways, including that some equipment is not suitable for use on ungrounded or corner grounded systems. IMO a much better solution is to use a 240 delta X 480Y/277 transformer.
Phase Perfect makes a wonderful product that can be used for some applications where most phase converters can't be used. Since I've had experience with these folks before, I know they are in the habit of supplying transformers sort of as a courtesy for customers that need to step-up the voltage to 480. This wouldn't be the first one I've seen them supply with a transformer that I think, for most applications, is not the best choice.
 
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