Motor OL Settings

[session88]

We have some new small motors installed on a new system that have Mechanical Breaks on them. The motors are 3 Phase 480 VAC and the motor breaks are fed off 2 of the 3 phases from the 480 VAC 3 Phase.

The breaks are constantly held open with 480 VAC single phase when the motors are running/energized.

The question is: Do we have to factor in the motor break current draw with the motor current draw combined when calculating the OL settings on the Motor Starters?

Thanks.

 

[iceworm]

We have some new small motors installed on a new system that have Mechanical Breaks on them. The motors are 3 Phase 480 VAC and the motor breaks are fed off 2 of the 3 phases from the 480 VAC 3 Phase.

The breaks are constantly held open with 480 VAC single phase when the motors are running/energized.

The question is: Do we have to factor in the motor break current draw with the motor current draw combined when calculating the OL settings on the Motor Starters?

Does the current for the brakes go through the overloads? I suspect, "yes" or you would not have asked. Given that, my answer is, "Yes, but it may not matter."

First I would be curious why you are asking. Is it a problem? Are the OVLDs tripping? If so, what did the commissioning crew say? Maybe new equipment new, install, and no commissioning - the EC just turned it over to the owner's crew.

Is the brake current a significant fraction of the motor current?

What do the design/installation drawings show? OP says a "new system" - any design documents at all?

There will be plenty looking for a code reference - but I think it is a design issue. Meeting code is at best marginal. Making it work safely and reliabily is much better. JMO

ice

 

[weressl]

We have some new small motors installed on a new system that have Mechanical Breaks on them. The motors are 3 Phase 480 VAC and the motor breaks are fed off 2 of the 3 phases from the 480 VAC 3 Phase.

The breaks are constantly held open with 480 VAC single phase when the motors are running/energized.

The question is: Do we have to factor in the motor break current draw with the motor current draw combined when calculating the OL settings on the Motor Starters?

Thanks.

The break should have its own contactor and overload protection and they should be interlocked, eg. when the break overload trips it should also open the main contactor.