Short Circuit Current Ratings

[JonR]

Hi,

I am working on the controls for a machine going to the USA, the company I work for is British.

Connected to the 208v rail in the panel are 2 x VFD's (fused) and a PSU (mcb)

The fuses for the 2 x VFD's are as recommended by the drive manufacturer, 15A, Class CC, IR 200kA

The mcb for the PSU is: Type C, 6A, ICU 30kA

When calculating the short circuit rating for the panel and fuses for the main fused isolator, would you use the worst case above, i.e. 200kA ??


Any assistance on this would be greatly appreciated.


Thank you in advance.

 

[jim dungar]

Companies like Schneider Electric/Square D, Allen Bradley, and Copper/Bussmann, all have links on their websites to NEC409 and UL508a which will help you to determine an SCCR for a control panel.

 

[Jraef]

Companies like Schneider Electric/Square D, Allen Bradley, and Copper/Bussmann, all have links on their websites to NEC409 and UL508a which will help you to determine an SCCR for a control panel.

Absolutely, it is not a simple process that you can pick up on a forum like this. But in this case I can tell you right now that since the SCCR rating cannot be higher than the lowest rated component (or set of series tested components), your limiting factor is going to be that MCB, not the fuses. I know of no MCBs with ratings that high. Keep in mind that IEC ratings don't count, you must use UL ratings of the components. Most MCBs are rated no more than 14 or maybe 18kAIC at 240V max.