3-phase GFCI Brkr. / Main bonding jumper

[slipknotbmg]

We have a 3-ph. 1800A 480V service coming into an MCC w/ a adj. trip GFCI main Brkr. Inline C.T.'s on 3-ungrounded and 1 grounded conductor. Our descrepancy is where the main bonding jumper should be located. I think on the service side of the ungrounded conductor before the Neutral C.T. assuming in a ground fault condition the breaker will operate normally and trip regardless of condition or even the existence of the CT. Another Forman is arguing that in order for the GFCI main to detect a ground fault, the bonding jumper needs to be on the secondary side of the CT. Any opinions would be greatly appreciated.

 

[ron]

Re: 3-phase GFCI Brkr. / Main bonding jumper

If this is a service, then the bonding jumper would go on the service side of the the neutral CT. This will allow that neutral CT to "see" normal unbalanced current, but no "see" ground fault current.
The CT's are electrically added together to result to 0. If it isn't 0, then there must be current going past the neutral CT on some other path, such as the EGC.

 

[jim dungar]

Re: 3-phase GFCI Brkr. / Main bonding jumper

You do not have a GFCI main. You have a main with GF or GFP.

GFCI is a specific term which aaplies to a Ground Fault Circuit Interuppter which is used for personel protection and trips at a 6mA level. GF, GFP, GFPE are undefined terms used for ground fault protection at levels above those for personel protection (GFPE is becoming commonly used to mean 30mA protection for equipment).

A properly tested ground fault system using primary injection (rather than just the GF relay test) would find an improper neutral-ground bonding after the neutral CT. This is one reason the NEC requires these "systems" to be tested.

[ January 25, 2006, 08:42 AM: Message edited by: jim dungar ]