We have a gear install that is essentially a Main Tie Main that are two 2000 amp 480 services. The strange design that we are dealing with is the Tie Breakers are in a remote piece of gear (Generator Gear) about 10 foot away that is also served by a generator. Basically this remote gear has 4 breakers...one load bank...one generator....and two tie breakers (one for each utility side on the other gear).
If either of the services goes down.... one side (or both) it/they can be fed from the Remote Generator Gear by closing the Tie Breakers and opening their counterparts in the Utility gear. The Generator is not separately derived so all the neutrals are bonded together. The Neutral bus does not run straight through the Main/Main (I removed "Tie" since it is really not there, the Tie is in the generator gear). There is a Main Bonding Jumper in each Utility CT cabinet bonding ground and neutral together.
The problem that is happening is the GFP are tripping on all the breakers because current is able to bypass the GFP CT sensors through the other Utility's Main Bonding Jumper because there is a parallel loop through the Tie Breaker Neutrals and current flows through the other MBJ.
We have lifted the Tie Breaker Neutral conductors to eliminate the loop. So we basically have Two Services with no Generator.
We believe the design engineers should have used 4-pole breakers on the Tie Breakers to eliminate this loop. They seem to think they can place other CT sensors in the design and with some programming fix the GFP. I think they are still going to have problems....along with a few code violations.
Any thoughts?
If either of the services goes down.... one side (or both) it/they can be fed from the Remote Generator Gear by closing the Tie Breakers and opening their counterparts in the Utility gear. The Generator is not separately derived so all the neutrals are bonded together. The Neutral bus does not run straight through the Main/Main (I removed "Tie" since it is really not there, the Tie is in the generator gear). There is a Main Bonding Jumper in each Utility CT cabinet bonding ground and neutral together.
The problem that is happening is the GFP are tripping on all the breakers because current is able to bypass the GFP CT sensors through the other Utility's Main Bonding Jumper because there is a parallel loop through the Tie Breaker Neutrals and current flows through the other MBJ.
We have lifted the Tie Breaker Neutral conductors to eliminate the loop. So we basically have Two Services with no Generator.
We believe the design engineers should have used 4-pole breakers on the Tie Breakers to eliminate this loop. They seem to think they can place other CT sensors in the design and with some programming fix the GFP. I think they are still going to have problems....along with a few code violations.
Any thoughts?
