INTEGRATED POWER SYSTEMS - SCCR RATING

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PE (always learning)

Senior Member
Location
Saint Louis
Occupation
Professional Engineer
Hey everyone,

I had a question about a project where I am being asked to provide short circuit current ratings for integrated power systems equipment. Basically what we have is a switchboard with four sections. We have a CT compartment section that feeds a 277/480V distribution section that feeds a transformer section that then feeds another section of the switchboard with 120/208V distribution. This is all a part of one switchboard called an integrated power systems switchboard by Siemens. The interrupting rating of the devices on the 277/480V side and the 120/208V are different. My question is what do I apply for the short circuit current rating of the switchboard? Do I treat the 277/480V side and the 120/208V side as separate switchboards and apply two separate SCCR ratings even though they are all technically a part of one integrated power system switchboard? Please let me know your thoughts.

Best Regards,
Engineer in training
 

ron

Senior Member
I agree with Jim.

We do the same in the data center market for PDU's. The input breaker is at 480V and the distribution is at 208V (on the secondary of the step down transformer), so it gets (2) ratings.

Sometimes if the transformer is so small that the 208V side is never going to let more than 10kA through, you can specify just the 480V rating and it is implied that the secondary will be the minimum of 10kA
 

smoothops10

Member
Location
FL
Occupation
EE
I agree with above posters allowing separate SCCR labels but if arc flash label with incident energy or HRC category is applied I would think you’d have to apply the single label unless the equipment is ‘compartmentalized’ sufficiently.
 
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