SCCR for panel with 3 separate feeds 480, 277, and 120V

[wecoyote5]

Hello all,

I have a panel that a customer will be supplying 3 separate feeds, 480V/3ph/20A for motors, 277V/1ph/5A for area lighting, and a UPS backed 120V/1ph/5A to feed a 24vdc power supply for controls. I have the 480 and 277 going through a class J fused disconnect so I'm covered, so far, for the SCCR rating (with subsequent fusing and components in the branch circuits like I've done previously) which currently is at 100kIA@480Vac. The question/problem comes in with the separate 120V feed. I cannot get a 5th fused pole for the disconnect so I have to use an Aux contact, then feed a class CC fuse and then the 24vdc power supply. Since, in my interpretation, this is being used for the controls only do I need to include this circuit in the SCCR calcs? I cannot find a definitive answer anywhere as most, if not all, the references refer to the use of a control transformer to get the 120V and not a separate feed.

Thanks all!

 

[petersonra]

only power circuits are evaluated for sccr.

 

[wecoyote5]

Hi Bob,

Thanks for your reply.

I completely agree with your comment and that's what I believe to be the case too, I just needed a second opinion to validate my interpretation.

 

[JoeStillman]

I thought all the equipment in the panel had to be rated for the worst SCCR of all the circuits? I think the idea is that short circuits don't recognize what conductor they're flashing over to.

 

[Jraef]

I thought all the equipment in the panel had to be rated for the worst SCCR of all the circuits? I think the idea is that short circuits don't recognize what conductor they're flashing over to.

Flashing over and short circuit are two different things. SCCR has nothing to do with wires, it’s only about power carrying components having the ability to NOT become shrapnel during a short circuit event.

Also in your case the 277 is covered in the SCCR of the 480V devices, meaning if your 480V SCCR is adequate, your 277V is going to be as well.

 

[wecoyote5]

Thanks for the feedback everyone.

Side note...Jraef, great signature line! It's really clever.