Ground fault protection

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faresos

Senior Member
Hi all;

There is an existing 3000A, 480/277V switchboard, and I need to add another section to house a new 2000A, 3 phase, 3W circuitbreaker which will feed a new 2000A, 3 phase, 3w switchboard. I have been told by the rep that I can't get the 2000A circuit breaker with GFP because this system is a 3 wire system and I have to have a reference to ground in order to do it. Also, he mention that I can't have TVSS for the 3 wire system. Can any one please explain why we can't have a GFP and a TVSS...thank you all in advance

p.s. (this project is a data center and I have been told to use a 3 wire system to reduce the ground fault, which i'm not sure why!!!!)

Thansk again,
 
sos,
doesn't make sense to me --- most all the data systems i have worked in have three phase four wire grounded services. and usually, when adding a new switchboard it is matched to the other switchgears specification. please post the reasoning of your engineer..... thanks, tuna
 
tuna,

Thanks for your reply. I really don't know the reason of using a 3- wire system to reduce the ground fault. I'll be meeting with the engineer next week
and I will try to understand the reason behind it but as of now, I don't see it would make any different than 4 wire system.
 
A three wire system and an ungrounded system are not necessarily the same thing.

You could have a delta-wye transformer with the center of the wye grounded, and only use the three phase wires to feed whatever.


Or you could leave the center of the wye completely unconnected. In this case, ground fault protection won't do you any good, because there is no path for current to flow to ground. (Current must flow in a complete loop. If one phase of the transformer accidently gets grounded, no current will flow to ground because there is no other path for the current to come back to the transformer secondary. )

I think you can still have TVSS. There are different modes for TVSS. For example, a good TVSS on a 4 wire + ground system usually places suppressors line-line, line-ground, line-neutral, and line-ground.

With a 3 wire system, you should still be able to get line-line protection.

Steve
 
Thank you Steve for your reply, it was very helpful. I have another question regarding the GFP; If I use 2000A GFP circuit breaker at the main switchboard to feed a switchboard located in different room and I need to use a main circuit breaker as disconnecting means (a 2000A circuit breaker) for that switchboard, does it have to be also GFP or not since the upstream breaker is GFP?

Thanks,
 
faresos said:
Thank you Steve for your reply, it was very helpful. I have another question regarding the GFP; If I use 2000A GFP circuit breaker at the main switchboard to feed a switchboard located in different room and I need to use a main circuit breaker as disconnecting means (a 2000A circuit breaker) for that switchboard, does it have to be also GFP or not since the upstream breaker is GFP?

Thanks,
Click to expand...
The only time you are required to provide GFPI after the main is in healthcare. And it has some exceptions.
 
McDowellb said:
The only time you are required to provide GFPI after the main is in healthcare. And it has some exceptions.
Click to expand...

What about 215.10? The OP did not indicate that there was GFP already in the system. This could be a switchboard with multiple mains that are rated at less than 1000 amps each. If a 2000 amp breaker were installed then it would require the GFP either by using 230.95 or 215.10 depending on the configuration.

Pete
 
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