I work as and E/E intern for a industrial panel company. A customer wants a 30kA SCCR panel. The input power is 3 phase 460V, an unknown distance from the main panel in the customer factory. Inside the NEMA 12 enclosure is a 2 phase transformer for 120v control voltage, fuse blocks, Motor protectors, motor controllers and a GFCI for the 120v power.
The only circuit breakers in the box are used post ac-dc converters. Everything else is either fused or behind a motor protector.
My initial understanding of SCCR was that the last component that needed the SCCR was the current protection device. I have recently been educated on that mistake as I recently found out that the wiring is also a factor.
The smallest panel I work on is a 460v 60A up to a 460v 400A panel. For simplicity sake lets say all wires from current limiting devices are 10 feet long with the only amp load for sizing.
I have found the part in the UL508A about transformers and I think I understand that part. The power from the transformer mostly stays inside the panel but does go out to multiple sensors and switches nearby.
Most of our components from the disconnect, primary fuses, and distribution block are already in the 100kA+ range.
Finally my question, I have a contactor that is a 5kA rating, controlling a 47A resistive heater load that is 10 feet away from the fuse block. What do I need to look at / calculate to see if it will meet the required 30kA for the box and wiring?
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