MCB specifications for motor feeding

Is their is any special specifications for miniture circuit breakers used for feeding motors ( 35-250 kW.

 

[jbartos]

Suggestion: Check with the miniature circuit breaker manufacturers what kind of specs they are using.

 

[electricpete]

In that size range usually there will be a separate starter providing overload protection. The breaker will have to provide instantaneous overcurrent protection.

 

[dydt]

'workin around these sizes of motor, i mostly see fuses as protection...there are some cases we have to replace some breakers specially for dc motors on a OEM machine 'coz the drive board is already "cooked" even before the breaker trips..

..you always have the option to browse some manufacturers for this size of motors...ac or dc..

dydt

 

[Marke]

Motors would normally be controlled by a motor starter which provides overload protection for the motor. Fuses or circuit breakers are used for branch protection, or for the protection of the cables supplying the motor. Because of the severe overload that can be experienced during a start, the standard quick acting fuses and circuit breakers can fail prematurely. Unless the cable is well oversized, it is necessary to use branch protection with a slow time constant. This can be achieved by using motor rated fuses or motor rated circuit breakers. Commonly, circuit breakers used with motor protection have an additional magnetic trip rated at 600% - 800% to provide fast short circuit protection in addition to the slow overcurrent protection.
Mark Empson

http://www.lmphotonics.com