Conductors Upstream of Fuse Block

[bsexton913]

I'm currently designing an HVAC "Appliance" with a calculated MOP of 70A. Unfortunately the breaker in the feeder panel supplying this unit is rated at 150A and can not be changed (there are politics at play and the customer does not want to go back and submit a variance and risk having his permit pulled).

Can I run conductors sized for 70A (#4) to a 70A fuse block inside the appliance or will I need 1/0? What if I install a 70 CB with 150A lugs in the device?

On a side note I'm trying to keep the SCCR of the panel at or above 35kA, so the fewer power blocks and terminations, the better.


Thanks in advance for the help

 

[augie47]

Short answer. If you read Art 240.4 you will see any conductor must have the ampacity of the overcurrent device protecting it unless otherwise noted.
It would seem, in your situation, you would need 1/0 conductors until such a point that you could apply the 240.21 tap rules to feed the required overcurrent device..