Disconnecting Means at ATS Load Side

[flengineer]

I have an ATS that is protected at both the normal and emergency line sides. I am feeding a MLO panel from the load side of the ATS. I know the cable is protected by the OCPDs on the line side, but is it good practice to provide a disconnecting means or MCB at the panel on the load side? To disconnect power to the panel, I would need to open the breakers at the generator and the normal power. Do ATSs normally have a way to disconnect the load side?

 

[steve66]

For critical loads, my personal preference it to not have a main breaker on the load side. If the branch breakers are not coordinated with the main, a short circuit on one of the branch circuits could trip the main breaker on the load side of the ATS. Then there would be no chance of providing generator power to any of the load on that panel. The entrie backup system has been prevented from doing its job.

I suppose one could specify a disconnect that doesn't have any overcurrent protection, but I don't really see any need to do this.

 

[ron]

For critical loads, my personal preference it to not have a main breaker on the load side. If the branch breakers are not coordinated with the main, a short circuit on one of the branch circuits could trip the main breaker on the load side of the ATS. Then there would be no chance of providing generator power to any of the load on that panel. The entrie backup system has been prevented from doing its job.

I suppose one could specify a disconnect that doesn't have any overcurrent protection, but I don't really see any need to do this.

I'm in agreement with Steve, but often a load side safety switch will not have adequate withstand for available short circuit current (be sure the ATS has it too).