Ground fault setting on generator breaker

[philly]

Do you typically see a ground fault setting on emergency generator (Diesel type) main breakers? If so are these ground fault settings only intended to alarm or to trip the generator breaker on ground fault?

Ideally in a system with downstream feeders the feeders themselves will have a second level of ground fault and will trip first for ground faults downstream of the feeders. But in a system that does not have ground fault on feeders and only on gen main what is the typical rule of thumb, or what does NEC dictate? Should this breaker alarm only, or trip for downstream ground faults? I don't think you would want it to trip and thus take out the whole emergency system?

What are the typical settings of these ground fault breakers weather they are set to trip or alarm? Do you set them at 1200A with a .3-.5s delay as you would with a utility main?

Is the NEC specific on when a second level of ground fault protection (ground fault on feeders) is required for emergency or normal systems?

 

[templdl]

Do you typically see a ground fault setting on emergency generator (Diesel type) main breakers? If so are these ground fault settings only intended to alarm or to trip the generator breaker on ground fault?

Ideally in a system with downstream feeders the feeders themselves will have a second level of ground fault and will trip first for ground faults downstream of the feeders. But in a system that does not have ground fault on feeders and only on gen main what is the typical rule of thumb, or what does NEC dictate? Should this breaker alarm only, or trip for downstream ground faults? I don't think you would want it to trip and thus take out the whole emergency system?

What are the typical settings of these ground fault breakers weather they are set to trip or alarm? Do you set them at 1200A with a .3-.5s delay as you would with a utility main?

Is the NEC specific on when a second level of ground fault protection (ground fault on feeders) is required for emergency or normal systems?

If you have GF on the down stream breasker's wouldn' t it the be a coordination issue wthe the genset breaker? Set the genset breasker's parameters above those of the downstream breakers, pick up and delays, to allow the down stream breaker to clear first.
We know if the genset breaker trips all downstream circuits are affected. With proper coordination that wouldn't be very likely to happen.
If you opt for an alarm on the genset breaker w/O a trip then what are you going to do with the alarm? How long would there be an alarm before it is responded to and what actions would be taken at that time?

 

[Bugman1400]

Not sure why you would not have GF protection on the feeders. Is the system solidly-grounded, impedance-grounded, or un-grounded? In general, gen-sets will have onboard protection to protect themselves. If you do not have adequate coordination with the downstream feeders then it may result in a trip of the gen-set which would affect all feeders. However, you may have a fault on one of the feeders that the feeder relay can detect but, the gen-set will not. In this case, the fault will burn back until the gen-set relay will detect.

 

[ron]

Is it an Emergency Generator (Article 700), Legally Required (701) or Standby (702)?

Depending, then look at 700.6(D), 701.6(D), or if it is a 702 generator, you would go to 215.10

 

[philly]

Not sure why you would not have GF protection on the feeders. Is the system solidly-grounded, impedance-grounded, or un-grounded? In general, gen-sets will have onboard protection to protect themselves. If you do not have adequate coordination with the downstream feeders then it may result in a trip of the gen-set which would affect all feeders. However, you may have a fault on one of the feeders that the feeder relay can detect but, the gen-set will not. In this case, the fault will burn back until the gen-set relay will detect.

System is solidly grounded. I have seen a lot of commercial applications (condos etc...) that only have ground fault setting on the generator breaker with the feeder breakers in the downstream Switchboard or panel not having ground fault. In these cases I would think that you don't want the generator breaker to trip on ground fault b/c a ground fault on a downstream feeder could trip the generator and render the emergency system useless. I would think that for these cases you would want to provide an alarm to indicate the presense of a ground fault. I guess if the ground fault is allowed to persist it will eventually turn into a phase fault and thus trip the respective feeder breaker.

Is it an Emergency Generator (Article 700), Legally Required (701) or Standby (702)?

Depending, then look at 700.6(D), 701.6(D), or if it is a 702 generator, you would go to 215.10

I believe this would fall under Article 700 so I'll have to look to see what is required.

Without any downstream feeder ground fault protection how would you go about setting the gen breaker ground fault? I've never been able to find good rules of thumb for setting LV ground fault on breakers.

 

[ron]

Without any downstream feeder ground fault protection how would you go about setting the gen breaker ground fault? I've never been able to find good rules of thumb for setting LV ground fault on breakers.

This is a good reference http://www.cooperindustries.com/con..._Ground_Fault_Protection_Requirements_GFP.pdf

What is the occupancy? If it is critical equipment, I set it at 1200A and 1 second delay (reference 230.95(A)).

If it is not critical, then I set it at 20% of the output handle rating with about 10-20 cycle delay to reduce false trips.

 

[philly]

Is it an Emergency Generator (Article 700), Legally Required (701) or Standby (702)?

Depending, then look at 700.6(D), 701.6(D), or if it is a 702 generator, you would go to 215.10

I took a look at 215.10. I knew that services rated 1000A or more required ground fault protection, but does this section indicate that any feeders rated 1000A or more require ground fault protection? For instance if I have a distribution panel located somewhere in a system, and this panel has multiple 1000A feeders, do all these feeders need to have ground fault protection?

 

[ATSman]

I took a look at 215.10. I knew that services rated 1000A or more required ground fault protection, but does this section indicate that any feeders rated 1000A or more require ground fault protection? For instance if I have a distribution panel located somewhere in a system, and this panel has multiple 1000A feeders, do all these feeders need to have ground fault protection?

I think the section you are referring to is 230-95 where it clearly states
"service disconnecting means" i.e.: a service entrance main breaker.
In article 700-26 it states "the alternate source for emergency systems shall not be required to have ground fault protection of equipment."

These references came from the 1984 NEC so they may have changed
since then.

 

[ron]

I took a look at 215.10. I knew that services rated 1000A or more required ground fault protection, but does this section indicate that any feeders rated 1000A or more require ground fault protection? For instance if I have a distribution panel located somewhere in a system, and this panel has multiple 1000A feeders, do all these feeders need to have ground fault protection?

215.10 applies to "all" feeder that are 1000A or more and more than 150V to ground. I put the "all" in quotes because you need to really read the conditions.

Most feeders, even if 1000A or larger and 480V do not get its own GF protection because of Exception 2, which effectively says that if it is already upstream, you don't need it on the individual feeder.

 

[ron]

I think the section you are referring to is 230-95 where it clearly states
"service disconnecting means" i.e.: a service entrance main breaker.
In article 700-26 it states "the alternate source for emergency systems shall not be required to have ground fault protection of equipment."

These references came from the 1984 NEC so they may have changed
since then.

I did mean 215.10 .....

 

[victor.cherkashi]

As I know you install ground protection right away on cable from first service switch, only once. Maybe you can do more but it not cost effective in most of the cases

Sent from my Nexus 5 using Tapatalk

 

[Bugman1400]

I still think you need to trip the gen-set for ground faults because you could have a ground fault upstream from the feeders. Simply raise the pickup and timedial above the feeders. This is something that is typically done in a coordination study.