rQx
Lifetime Supporting Member
Hi,
I'm a little bit confused on how understand the short-circuit ratings on some components in my cabinet and hoping for some advise. I have looked in the manual for the ratings and I got for my motor groups:
Motor Protection Circuit breaker - 15kA
Contactor - only found for fuses in the manual
Motor Protection Circuit breaker - 15kA
Contactor - only found for fuses in the manual
Soft starter 5kA
Motor Protection Circuit breaker - 15kA
VFD - 100kA
Ok, so I got some numbers. So if my soft starter can handle 5kA I would say that this is the highest shorrt circuit current I would rate my cabinet for. But it is protected by a MPCB so I think it's wrong to do it this way?
So I looked at the SCCR tool at Allen Bradleys webpage. There they say that if I use a MPCB and a contactor I can have 65kA. How is this possible since in the technical specs for the MPCB it's rated 15kA?
Further more, when I choose the SMC-3 soft starter, there is only options with UL class J fuses and not with MPCB?
Even further more, the load switch is only rated for 15kA and a fuse that I have is only rated for 10kA.
So basicly the more I write I guess it comes down to my soft starter. If this can only handle 5kA then I must rate my cabinet for this, because I can't get a test report from rockwell on MPCBs for the SMC-3? With Class J fuses it can handle 65kA.
So if I use Class J fuses all my motor groups would be 65kA but the cabinet is still limited to 10kA for the fuses I use. And if I switch the fuses to higher kA then it would be rated for 15kA because that is what my load switch is
Is my thinking somewhat correct?
/Tim
I'm a little bit confused on how understand the short-circuit ratings on some components in my cabinet and hoping for some advise. I have looked in the manual for the ratings and I got for my motor groups:
Motor Protection Circuit breaker - 15kA
Contactor - only found for fuses in the manual
Motor Protection Circuit breaker - 15kA
Contactor - only found for fuses in the manual
Soft starter 5kA
Motor Protection Circuit breaker - 15kA
VFD - 100kA
Ok, so I got some numbers. So if my soft starter can handle 5kA I would say that this is the highest shorrt circuit current I would rate my cabinet for. But it is protected by a MPCB so I think it's wrong to do it this way?
So I looked at the SCCR tool at Allen Bradleys webpage. There they say that if I use a MPCB and a contactor I can have 65kA. How is this possible since in the technical specs for the MPCB it's rated 15kA?
Further more, when I choose the SMC-3 soft starter, there is only options with UL class J fuses and not with MPCB?
Even further more, the load switch is only rated for 15kA and a fuse that I have is only rated for 10kA.
So basicly the more I write I guess it comes down to my soft starter. If this can only handle 5kA then I must rate my cabinet for this, because I can't get a test report from rockwell on MPCBs for the SMC-3? With Class J fuses it can handle 65kA.
So if I use Class J fuses all my motor groups would be 65kA but the cabinet is still limited to 10kA for the fuses I use. And if I switch the fuses to higher kA then it would be rated for 15kA because that is what my load switch is
Is my thinking somewhat correct?
/Tim