SCCR control XFMR calculation ?

[milmat1]

Typical MCC / control panel design with fused disconnect cabinet. Branch circuit OCP, to drives , motors etc. This is all good.
My confusion comes at the control transformer. I have an dry type control transformer 1KVA, Maybe a utility 120V outlet etc then a 24VDC power supply.
All the control / IO etc is 24VDC. According to the UL 508A SB4.3 flowchart the transformer does not require an SCCR rating, right? But then does this mean that anything beyond the control transformer also is excluded ?

 

[petersonra]

Control circuits do not have to be considered in sccr calculations, only power circuits

 

[milmat1]

Thanks. Just like to be sure. I have only recently started doing this part of the design.

Thanks again..

 

[Jraef]

Control circuits do not have to be considered in sccr calculations, only power circuits

The only thing that technically counts in a CPT circuit are the primary fuses and holders. Class CC fuses are usually 200kA, so it is the holders, and most of them are listed WITH the fuses for what the fuse is listed at, so bottom line, not a problem.

I only mention it because I have seen people use the WRONG fuseholders, i.e. those made for NON-Branch rated "midget" fuses that are the same PHYSICAL SIZE as Class CC fuses, to where the holders were rated for far less than the fuses they used.

 

[petersonra]

The primary side of a cpt is usually a power circuit.