Switchboard 1

[Reesh14]

I have a 1200 A main switchboard. I am supposed to provide Ground-fault protection for this equipment according to 230.95 NEC. I am not sure what this entails. From my understanding the ground fault protection device is used in the service disconnect of the switchboard. Special sensors are used and special breakers are used to provide ground-fault protection? I am working on a design, and would like to know how to show on a plan how to provide ground-fault protection of the switchboard. Thanks.

 

[alehman]

There are lots of ways to do ground fault protection. You can specify a main circuit breaker with a trip unit with integral ground fault protection. You could also use a bolted pressure switch with shunt trip and a ground fault relay.

Two common methods for ground fault sensing (for either of the above options):

Residual mode, where the ground current is computed by the relay as the vector sum of phase and neutral currents (most common for circuit breaker applications).

Zero sequence CT, where one large CT surrounding phase and neutral conductors is used and wired to the relay or trip unit (most common for switches).

Or... you could specify a main lug only panel with a maximum of six feeder devices. If the feeders are less than 1000A, GF protection is not required per the NEC (for most applications).