Multi Function Protection Relays for MCCB

[undervoltage]

Do we traditionally install a Multifunction Protection Relay on a Low Voltage MCCB? Will it operate like a Power Circuit Breaker from a Protection Relay?

Thanks

 

[dpc]

Do we traditionally install a Multifunction Protection Relay on a Low Voltage MCCB?

No.

Will it operate like a Power Circuit Breaker from a Protection Relay

The MCCB can be tripped by a protective relay (or any contact) only if it has an optional shunt trip coil.



David Castor

http://www.cvoes.com

 

[oldfieldguy]

In most applications, the external protective relay comes off as overkill. However, there are some cases where the coordination of protection requires settings not available in the integral trip unit.

Most manufacturers sell shunt trip units for their breakers.

old field guy

 

[jghrist]

MCCBs don't have a withstand rating, so instantaneous cannot be disabled when applying an external relay.

 

[davidbeach]

MCCBs don't have a withstand rating, so instantaneous cannot be disabled when applying an external relay.

True, but not always obvious. In part it depends where the hybrid Insulated Case Circuit Breaker falls. There are families of MCCB/ICCB breakers where it appears possible to turn off the instantaneous trip. What happens is that there is also an Instantaneous Override trip that isn't always clearly obvious in the documentation that will trip the breaker at its fixed setting. This fixed setting may be relatively high and of not much concern, or it may be surprising low and not much above the highest instantaneous setting.