SCCR for industrial panel

[BetterEngineer]

Hi,
I am designing a 480 VAC panel for VFDs and Servos. The main rotary disconnect is 200 kA , 30 Amp and further down the breakers are 65kA short circuit rating.
This panel is powered from a PDP with 30 Amp fused disconnect and probably has 65kA SCCR.
What should be the SCCR of the breakers down stream? Higher than the SCCR of the PDP disconnect?

 

[don_resqcapt19]

You have to do the calculations for the system. The rating of the equipment must be equal to or greater than the fault current that is available at that point on the system.

 

[BetterEngineer]

Thanks @don_resqcapt19
I have got mixed responses for the available fault current at the bus providing power to the breakers in PDP. I have eventually selected 65kA breakers for the system.

now I have 200 kA disconnect and then 65kA breakers (140 M’s ) that feeds to VFDs and Servos. I am not using combination components for my system. Is there any rule that says we have to use the combination components?
i want to use Allenbradley breakers with Siemens drives and Allen Bradley drives as well..

 

[EC Dan]

The drives are going to be the weak point in your system with respect to SCCR. It's highly unlikely you will have combination ratings for your Siemens drives with the AB 140M starters, which means default ratings of 5 kA for those drives. The only rule is to have a panel SCCR above the available fault current, but if you have high fault current you will only satisfy that rule by selecting tested combination starters.

 

[BetterEngineer]

Right! I have not yet received the available fault current at the busway so I will have to use combination starters.. Rockwell recommends 140U for the Servos.. I guess I will go with what Rockwell and Siemens recommends in this case

 

[xformer]

Hi,
I am designing a 480 VAC panel for VFDs and Servos. The main rotary disconnect is 200 kA , 30 Amp and further down the breakers are 65kA short circuit rating.
This panel is powered from a PDP with 30 Amp fused disconnect and probably has 65kA SCCR.
What should be the SCCR of the breakers down stream? Higher than the SCCR of the PDP disconnect?

The impedance of the conductors should lower the available fault current as one proceeds down stream. Calculations are required to determine the amount.

 

[don_resqcapt19]

Thanks @don_resqcapt19
I have got mixed responses for the available fault current at the bus providing power to the breakers in PDP. I have eventually selected 65kA breakers for the system.

now I have 200 kA disconnect and then 65kA breakers (140 M’s ) that feeds to VFDs and Servos. I am not using combination components for my system. Is there any rule that says we have to use the combination components?
i want to use Allenbradley breakers with Siemens drives and Allen Bradley drives as well..

The ratings of the breakers have nothing to do with this. You have to have the actual fault current at the point where you want to install the equipment, and then select equipment with an SCCR higher than the available fault current. The only way to do this is to run the fault current calculations.