Yes, the scenario you described strongly suggests a coordination problem between the switchgear (SWGR) feeder breaker and the Motor Control Center (MCC) main circuit breaker (MCB). Here's why: Expected Coordination

In a properly coordinated system, the breaker closest to the fault should trip first. This isolates the problem and minimizes disruption to the rest of the electrical system. In your case, the fault (the inrush current from starting the motors) was presumably downstream of the MCC main breaker. Therefore, the MCC MCB should have tripped before the SWGR feeder breaker.

What Likely Happened

The SWGR feeder breaker tripped first, indicating that it responded to the overcurrent condition (motor starting inrush) faster than the MCC MCB. This could be due to several factors:

Incorrect Breaker Settings

The SWGR feeder breaker might have settings that are too sensitive (too low instantaneous trip, or too aggressive time-current curve). The MCC MCB may have settings that are too high or a slower response time.

Breaker Aging/Degradation

One or both breakers might not be performing according to their original specifications due to age, wear, or environmental factors. This can alter their tripping characteristics.

Mismatched Breaker Types

The SWGR feeder breaker might be a faster-acting type (e.g., electronic trip) compared to the MCC MCB (e.g., thermal-magnetic).

Insufficient Time Delay for the MCC MCB

The MCC MCB might not have sufficient time delay built into its tripping curve to ride through the motor starting inrush current.

Fault Current Magnitude

The magnitude of the fault current at the SWGR might have been higher than expected due to system impedance or other factors. This could cause the SWGR breaker to trip faster than anticipated, even if the coordination was designed correctly.

Consequences of Poor Coordination



Unnecessary Outages

The tripping of the SWGR feeder breaker shuts down the entire MCC, affecting all the loads connected to it, even if the fault is only related to the motors.

Increased Stress on Equipment

Repeatedly tripping the SWGR feeder breaker can stress the breaker and other upstream equipment, potentially reducing their lifespan.*

Safety Hazards

In some fault conditions, poor coordination can lead to higher fault currents and longer fault clearing times, increasing the risk of damage to equipment and potential safety hazards for personnel.

Next Steps


Review Breaker Settings

Carefully review the time-current curves and settings of both the SWGR feeder breaker and the MCC MCB. Ensure that the MCC MCB has a suitable delay to ride through the motor starting inrush current, while still providing adequate protection against sustained overloads and short circuits. You'll need to consult the manufacturer's documentation for the breakers to understand their specific characteristics.2.

Coordination Study

Perform a coordination study to verify that the breakers are properly coordinated. This study involves analyzing the time-current curves of all the protective devices in the system and ensuring that the downstream devices trip before the upstream devices for various fault current levels. This study usually involves specialized software (SKM, ETAP, EasyPower) and the skills of a qualified electrical engineer.3.

Breaker Testing

Have the breakers tested to verify that they are operating according to their specifications. This is especially important for older breakers.4.

Consider Upgrading Breakers

If the existing breakers are not capable of being coordinated properly, consider upgrading to newer breakers with adjustable settings or better tripping characteristics.5.

Motor Starting Methods

Investigate alternative motor starting methods (e.g., reduced voltage starters, soft starters) to reduce the inrush current and make coordination easier.6.

System Impedance: Analyze the system impedance to understand how it affects the fault current levels at different points in the system. This can help you determine if the breakers are adequately rated and coordinated for the actual fault current conditions.By addressing these issues, you can improve the coordination of your electrical system and reduce the risk of unnecessary outages and equipment damage. Flag for review