SCCR calculations.

Hi all,

I may have put myself in a small bind. But would like some thoughts.
First off I do not know the AFC at this particular customer facility. But most of the customers we work with require 50-65kA suitable panels..
I have a panel using mostly all AB products. Pretty small control panel. But have realized the 1489 circuit breakers I'm using only have a 10kA rating. All my other branches are covered to at least 65kA except these two. I am using J-type 30a fuses in my main fused disconnect. No transformer feeding this panel so I cannot use peak let through from isolation transformer.

I do not think I can use peak let through of the class J main fuses either since the IP Isc and clearing time are all greater than the 10kA using the charts, as long as I'm reading them properly.
Will I have to change these breakers out with fuses to bring it up?

Sorry no PLC question here.
Thanks!

Yeah, people want to use those little IEC DIN rail mounted breakers because they are cheap and small, but you've hit on the down side. No reasonable IC rating. The other issue is that if it's 480V, they are ONLY listed for 480/277V systems, not 480V Delta as you occasionally find in the US.
You can get 65kA SCCR out of Bul. 140M Motor Protection Circuit Breakers if it's a motor starter, but if it requires a branch protection device you may need to go to an MCCB.

Jraef,

I am using the 140M ahead of my PF525 in another circuit. These other two branch breakers are just protecting individual 24vdc power supplies..
So do you mean use an MCCB on the main instead of the class J fuses?
Thanks,

Make sure the MCCB is listed as fault current limiting also, I know not all are.

I believe I was reading the chart incorrectly.
I think that if my I-RMS and I-P let through of the fuse LPJ 30sp is below the 10kA of my circuit breakers at my given AFC (assuming 65kA) then I am ok to use the sccr of the fuse..?

Correct.

Great!
Thanks for confirming Rob.