"Tie" on GFCI systems

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augie47

augie47

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In reviewing some drawings with contractor, I have something thats troubling me that I can't put my finger on. The building is designed with (2) 480Y/277 transformers/service centers.
Both services exceed 1200 amp and will have G-F mains. The plans show a "tie breaker" connecting the two systems. Under normal operation, the second service disconnect is open and everything is fed from the 1st service thru the tie-breaker.
In that the second service has the neutral bonded, will this not cause a problem with the G-F device on the 1st service and are we not violtaing 250-24(a).5?
 
Re: "Tie" on GFCI systems

You will need to have a ground fault relay scheme designed for a Main-Tie-Main service. One of the easiest to implement and maintain is called a Modified Differential Ground System. These are easy to implement with stand-alone GF relays but they are possible with the ones internal to breakers. Just make sure you include this in your specifications.

Also, just a side note. GFCI is a term reserved for devices that provide 4-6mA trip protection for personell. GF or GFP are used for larger trip values.

[ February 07, 2006, 10:03 AM: Message edited by: jim dungar ]
 
Re: "Tie" on GFCI systems

Originally posted by jim dungar:Also, just a side note. GFCI is a term reserved for devices that provide 4-6mA trip protection for personell. GF or GFP are used for larger trip values.
Click to expand...
Then what is a "GFI"? :D
 
Re: "Tie" on GFCI systems

I don't know for sure. I have used it as slang to define GF protection which is integral to a breaker (i.e. solid state) but is not a GFCI versus GF protection that uses separately mounted relays and "shunt trips".

GFCI - Ground Fault Circuit Interupter is defined by UL 943. Class A GFCIs (people protection)trip at a nominal 5mA

GFPE - is a slang term often used for devices with 30mA trip levels, UL calls these Equipment Ground Fault Protective Devives

GF, GFP, and GFI - slang term terms usually reserved for ground fault relay and sensing equipment used to meet NEC 230 requirements.
 
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