Mike Dolt Enterprises
Mike Dolt Enterprises
User: PE (always learning), Location: Saint Louis
Asked on: Wednesday, June 2, 2021 at 11:45 pm EDT
Answered on: Thursday, June 20, 2024 at 11:44 am EDT
Question: Hey everyone,I'm getting tunnel vision on a potential issue and I'm needing a little guidance. My issue pertains to ground fault selective coordination in healthcare facilities. I have a healthcare facility where I have two levels of ground fault protection, which are required to be coordinated within the system. Normally, the phase curves are coordinated, and the ground fault curves are coordinated separately. However, in cases where a protective device does not have a ground fault trip sensor, a ground fault on its load side will be treated the same as a phase fault. Therefore, it's imperative the phase trip curve be coordinated with the upstream ground fault protection. This is my understanding at least so correct me if I'm wrong.Most of this equipment is existing so the design is what it is. My scenario has a 4000 amp fuse (480V three phase, four wire) on a switchboard (HMP) that has a feeder breaker of 1200 amps that then feeds over to a main lug only panel (MPP2) with a 600 amp breaker. The 4000 amp fuse and the 1200 amp breaker both have ground fault protection. The 600 amp breaker does not have any ground fault protection as it is not required.Do I need to coordinate the 600 amp breaker's phase settings with the ground fault sensors on the 1200 amp and 4000 amp overcurrent protection upstream? It's pretty much impossible for me to do given the parameters of the settings on the 600 amp breaker and it would also destroy any coordination that I have with the other phase settings for overcurrent protection downstream.I have attached a picture of the one line and the time current curves for reference.
Understanding Ground Fault Selective Coordination in Healthcare Facilities
In healthcare facilities, it is essential to maintain selective coordination between ground fault protection devices to ensure that only the closest downstream device trips in the event of a ground fault, preventing unnecessary power outages. This is achieved by coordinating the phase and ground fault trip curves of the devices.
Your Scenario
In your scenario, you have a 4000 amp fuse (HMP) with ground fault protection, a 1200 amp breaker (MPP1) with ground fault protection, and a 600 amp breaker (MPP2) without ground fault protection.Since the 600 amp breaker does not have ground fault protection, a ground fault on its load side will be treated as a phase fault. Therefore, it is necessary to coordinate the phase trip curve of the 600 amp breaker with the ground fault protection upstream.
Coordination Considerations
Coordinating the phase trip curve of the 600 amp breaker with the ground fault protection upstream is challenging because: The 600 amp breaker does not have any ground fault trip settings. The parameters of the settings on the 600 amp breaker may not allow for proper coordination.
Recommended Approach
Given the constraints of your scenario, the recommended approach is to: Verify the downstream load characteristics
Determine the fault currents and trip settings of the devices downstream of the 600 amp breaker.
Assess the potential consequences of not coordinating
If the 600 amp breaker trips prematurely during a ground fault, it could result in unnecessary power outages to downstream loads.
Evaluate alternative solutions
Consider using other methods to provide ground fault protection for the downstream load, such as: Installing a ground fault relay on the 600 amp breaker. Installing a separate ground fault protective device downstream of the 600 amp breaker.
Consult with a qualified electrical engineer
Seek professional guidance to determine the best solution for your specific situation.
Conclusion
Coordinating the phase trip curve of a protective device without ground fault protection with upstream ground fault protection is challenging. It is important to carefully assess the potential consequences and consider alternative solutions to ensure proper ground fault selective coordination in your healthcare facility. Flag for review