GROUND FAULT SELECTIVE COORDINATION IN HEALTHCARE FACILITIES

[PE (always learning)]

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.

 

[mbrooke]

How old is the equipment? I'd see if you can grandfather the requirments. I'm sure you know this, but on the essential system you can alarm instead of tripping on a GF.

 

[ron]

As you mentioned, 2 levels of GF is required and that is what you coordinate.
I would think that zero sequence (GF) and positive / negative sequence current do not need to be shown on the same TCC.

 

[xptpcrewx]

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.

The IEEE Buff Book suggests that phase and ground elements should both coordinate with one another, so only evaluating phase and ground elements separately would be inadequate. The whole purpose of selective coordination is to confine outages to their immediate zones of protection and affected areas. In general, phase and ground settings will impose constraints on each other.

 

[PE (always learning)]

The IEEE Buff Book suggests that phase and ground elements should both coordinate with one another, so only evaluating phase and ground elements separately would be inadequate. The whole purpose of selective coordination is to confine outages to their immediate zones of protection and affected areas. In general, phase and ground settings will impose constraints on each other.

I totally agree with you, my only issue is that it's pretty much impossible for me to coordinate the 600 amp breaker's phase settings with the ground fault settings of the upstream overcurrent protection. The only thing I can think is to add a ground fault sensor to the 600 amp breaker downstream to ensure total selective coordination. They are planning on replacing existing panel "HMP" which gives me a chance to suggest adding the ground fault relay.

The construction drawings specifically state that, "The project shall provide selective coordination for all new overcurrent protective devices installed as part of the essential electrical system as defined by 2011 NEC, Article 517. I don't know if the code makes a difference or not, but just thought I'd give more information.

 

[xptpcrewx]

I totally agree with you, my only issue is that it's pretty much impossible for me to coordinate the 600 amp breaker's phase settings with the ground fault settings of the upstream overcurrent protection. The only thing I can think is to add a ground fault sensor to the 600 amp breaker downstream to ensure total selective coordination. They are planning on replacing existing panel "HMP" which gives me a chance to suggest adding the ground fault relay.

The construction drawings specifically state that, "The project shall provide selective coordination for all new overcurrent protective devices installed as part of the essential electrical system as defined by 2011 NEC, Article 517. I don't know if the code makes a difference or not, but just thought I'd give more information.

I think the construction documents (and 2011 code) would only apply to the original installation, particularly if you were replacing devices with like/kind or if you were bringing the original design back into compliance. As soon as you change the design by adding a new GFPE device or issuing new settings for existing devices, I believe you would be required to follow whatever the current edition of the NEC is adopted by your jurisdiction. The AHJ typically requires a P.E. certify that selective coordination is achieved or does the review themself. Keep in mind coordination is only required down to 0.1 seconds for essential systems.

What you basically need to do is ensure the phase pickup/TD for the 600A OCPD’s TCC is set below and to the left of the phase AND ground pickup/TD for the 1200A OCPD for time greater than 0.1 seconds. Also, if the feeder cable presents enough impedance, the fault current would be reduced at the location of the 600A OCPD, and you wouldn’t need to coordinate for currents beyond this value (since the TCC would be truncated). Ensure you have accurate feeder length, wire size, parallel sets, raceway type, operating temperature etc.

 

[mbrooke]

IMO, unless GF is added to the upstream devices, selective coordination can not be achieved. If HMP is more than 30 years old, in theory replacement would not be a bad idea.

 

[PE (always learning)]

I think the construction documents (and 2011 code) would only apply to the original installation, particularly if you were replacing devices with like/kind or if you were bringing the original design back into compliance. As soon as you change the design by adding a new GFPE device or issuing new settings for existing devices, I believe you would be required to follow whatever the current edition of the NEC is adopted by your jurisdiction. The AHJ typically requires a P.E. certify that selective coordination is achieved or does the review themself. Keep in mind coordination is only required down to 0.1 seconds for essential systems.

What you basically need to do is ensure the phase pickup/TD for the 600A OCPD’s TCC is set below and to the left of the phase AND ground pickup/TD for the 1200A OCPD for time greater than 0.1 seconds. Also, if the feeder cable presents enough impedance, the fault current would be reduced at the location of the 600A OCPD, and you wouldn’t need to coordinate for currents beyond this value (since the TCC would be truncated). Ensure you have accurate feeder length, wire size, parallel sets, raceway type, operating temperature etc.

Can I tell them to add a ground fault sensor to the 600 amp circuit breaker sense they are replacing that panel anyways? Then I could coordinate this ground fault sensor with upstream ground fault sensors.

 

[xptpcrewx]

I might not be fully understanding the issue you are dealing with. Not sure how adding another layer of ground fault protection is going to resolve an existing upstream miscoordination issue.

 

[PE (always learning)]

I might not be fully understanding the issue you are dealing with. Not sure how adding another layer of ground fault protection is going to resolve an existing upstream miscoordination issue.

Thank you again for all of you that responded. I appreciate the feedback as this is kind of a hard one to explain without sitting down and talking.

I can coordinate the ground fault settings between main and feeder breaker panel HMP just fine. I have an issue when I go from HMP to MPP2. The phase settings on the 600 amp breaker don't coordinate with the upstream ground fault settings for the 1200 amp feeder breaker located in panel HMP. I'm suggesting adding a ground fault sensor to the 600 amp breaker because I can get the ground fault settings to coordinate with both upstream ground fault sensors in panel HMP. Adding another ground fault sensor would allow the 600 amp breaker to trip first and coordinate with upstream devices.

Picture of oneline and pdf of TCC added for reference.

 

[xptpcrewx]

Thank you again for all of you that responded. I appreciate the feedback as this is kind of a hard one to explain without sitting down and talking.

I can coordinate the ground fault settings between main and feeder breaker panel HMP just fine. I have an issue when I go from HMP to MPP2. The phase settings on the 600 amp breaker don't coordinate with the upstream ground fault settings for the 1200 amp feeder breaker located in panel HMP. I'm suggesting adding a ground fault sensor to the 600 amp breaker because I can get the ground fault settings to coordinate with both upstream ground fault sensors in panel HMP. Adding another ground fault sensor would allow the 600 amp breaker to trip first and coordinate with upstream devices.

Picture of oneline and pdf of TCC added for reference.

Your solution makes sense to me. Only suggestion would be to lower the ground pickup and time delay for MPP2 if possible. I’d be curious to see the phase TCC’s...

 

[PE (always learning)]

Thanks again for input, Phase settings attached for reference

 

[xptpcrewx]

Thanks again for input, Phase settings attached for reference

Overall, it looks good.

Side note: I don’t really understand why phase coordination is only required down to 0.1 seconds for essential systems. On your phase TCC’s you can see miscoordination will occur for fault currents intersecting the instantaneous region (assuming those protective devices are not coordinated tested pairs). So, without addressing instantaneous coordination (full selectivity), any effort to coordinate these devices outside the instantaneous region is basically useless as a high magnitude fault would probably force a larger than necessary service interruption to occur regardless.