Info- Ground Fault Protection

[mstrlucky74]

Regarding switchboards, what is 2nd level ground fault protection exactly?

 

[jim dungar]

Regarding switchboards, what is 2nd level ground fault protection exactly?

GF on the main device, would be level 1.
GF on the feeder devices would be level 2.

 

[mstrlucky74]

GF on the main device, would be level 1.
GF on the feeder devices would be level 2.

Can you elaborate a little more? Thanks

 

[SparkyHC]

a "for instance..."

a "for instance..."

Can you elaborate a little more? Thanks

A while ago we added a second level of ground fault protection to a hospital...
A large feeder supplied (6) or more OR's with support rooms containing radiology equipment. The problem is any
ground fault in any of the above rooms or equipment shuts them all down. Imagine that...
After a more in depth review, it was most often the radiology equipment that was causing most of the problems. So the individual
branch circuits supplying the radiology were recommended to be replaced with GFPE at a lower threshold. This way a single room does not
shut down an entire wing....

 

[JoeStillman]

Can you elaborate a little more? Thanks

The 1st level protection (main breaker) is required to clear a 1200A ground fault with a maximum delay of 1 second for faults of 3,000A or more (230.95(A).) The 2nd level protection (branch breakers) is required to be set lower than 1200A and faster than 1 second so that ground faults in the branches won't trip the main (517.17(C).) This is a good application for zone-selective interlocking, which is available on many electronic trip power circuit breakers.

 

[mstrlucky74]

The 1st level protection (main breaker) is required to clear a 1200A ground fault with a maximum delay of 1 second for faults of 3,000A or more (230.95(A).) The 2nd level protection (branch breakers) is required to be set lower than 1200A and faster than 1 second so that ground faults in the branches won't trip the main (517.17(C).) This is a good application for zone-selective interlocking, which is available on many electronic trip power circuit breakers.

So 2nd level is on branch breakers. Is that accomplished by using a GFCI breaker? So whenever there is a GFCI breaker that is 2nd level ground fault protection? Thanks

 

[don_resqcapt19]

So 2nd level is on branch breakers. Is that accomplished by using a GFCI breaker? So whenever there is a GFCI breaker that is 2nd level ground fault protection? Thanks

Normally we are not talking about GFCI protection when we are talking about second level ground fault protection and most of the time the second level protection would be on feeder breakers, not branch circuit breakers. We are talking about ground fault protection in 10s to 100s of amps or even more, not GFCI protection of 5mA.

 

[mstrlucky74]

Normally we are not talking about GFCI protection when we are talking about second level ground fault protection and most of the time the second level protection would be on feeder breakers, not branch circuit breakers. We are talking about ground fault protection in 10s to 100s of amps or even more, not GFCI protection of 5mA.

Thanks so why is Joes post saying branch breakers?

 

[JoeStillman]

Thanks so why is Joes post saying branch breakers?

Sorry, I failed to use the correct terminology. Branch-circuits are defined in the code as "The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s)." It was not my intention to refer to branch circuits as the location for 2nd level protection.

The breakers downstream of the main in a switchboard or switchgear are seldom "branch-circuit" breakers. More often they are "feeders", defined in the code as "All circuit conductors between the service equipment, the source of a separately derived system, or other power supply and the final branch-circuit overcurrent device."

What I meant was the feeder breakers immediately downstream of the mains ought to have Ground-Fault protection, not the branch-circuits. I don't usually use the term "feeder breakers" for these because, to me, "feeder" seems to connote the incoming circuits, while "branches" connotes any outgoing circuit.

Someday I'll get it through my head.

 

[mstrlucky74]

Sorry, I failed to use the correct terminology. Branch-circuits are defined in the code as "The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s)." It was not my intention to refer to branch circuits as the location for 2nd level protection.

The breakers downstream of the main in a switchboard or switchgear are seldom "branch-circuit" breakers. More often they are "feeders", defined in the code as "All circuit conductors between the service equipment, the source of a separately derived system, or other power supply and the final branch-circuit overcurrent device."

What I meant was the feeder breakers immediately downstream of the mains ought to have Ground-Fault protection, not the branch-circuits. I don't usually use the term "feeder breakers" for these because, to me, "feeder" seems to connote the incoming circuits, while "branches" connotes any outgoing circuit.

Someday I'll get it through my head.

Thanks Joe. So 1st level would be the main at the service switchgear and 2nd would be the breakers for all the feeders?

 

[JoeStillman]

Thanks Joe. So 1st level would be the main at the service switchgear and 2nd would be the breakers for all the feeders?

That's how I interpret it, yes.

 

[kingpb]

The intent would be to coordinate the ground fault protection just as you would coordinate the phase - phase, or 3 phase fault relays/protection.