Short Cicuit Current Rating for control panel

[StanleySmith]

NEC 2005 Aricle 409 requires SCCR rating label on control panel, so far 31 states have adopted this. I'm doing SCCR calculation on my panel (50 KA SCCR required) and have a very fundamental question:
My panel has 2 transformers: one auxiliary disconnect and one control. The PRIMARY sides of these two transformers are protected by fuses that have SCCR rating of greater than 50 KA (200 KA actually). Now on the SECONDARY sides of these transformers, I DO NOT have to use fuses or circuit breakers that has SCCR rating of 50 KA or greater. Am I right???

Thank you,

 

[davidbeach]

What is the let-through fault current on the secondary of each transformer?

 

[jraef]

You are correct as far as this particular panel goes. In the changes under UL508A made to accommodate Article 409 with regards to the SCCR, paragraph SB3.2.1 specifically states that only the PRIMARY SCPD of the transformers needs to be included. The secondary side, and all devices connected to the secondary, are NOT part of the SCCR calculations.

If the transformers were feeding other equipment panels outside of this panel, that becomes a new "service" so you may have an issue on being able to list those other panels.

BTW, 50kA? Wow, harsh!

JRaef.com
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