Action Dave, I meant to say "transformer" not generator. Long day. I'm trying to determine if I need to have an equipment ground between the transformer and the main gear under the proposed 3-ph, 3-wire scenario. I'm trying to turn the secondary from a wye to a delta and corner ground it.
Infinity, yes, the X/F has been connected as a wye but I"m trying to go to a 3-wire delta service.
Electrofelon, that is exactly what I'm trying to do. The reason is we have two utility services (main-tie-main) and we are adding a generator as a third source. The existing main breakers are 3000A with GF. The switchgear mfr is saying the proposed generator breaker is not compatible with the existing breakers for modified differential ground fault, and they must be replaced. I'm trying to eliminate the ground fault requirement altogether to avoid spending six figures replacing two relatively new 3000A breakers. I would rather not take this approach but budget leaves us no choice. Leaving the X/O floating at the transformer is what I'm trying to figure out. Do I disconnect it? I still want to use the grounding electrode at the service and corner ground the delta at the switchgear.
If it were me I would not consider the change to a floating delta supply, so that would leave me with only looking at the alternates. If I read correctly, when you convert to floating delta at the MTM, the existing mainbreaker GF trip will be disabled?
Look at the problem from the load side, from the main and its MDP main distribution feeders. If I read correctly supply is currently 480 / 277 Y solidly grounded. The existing neutral conductor is already at the MD switchgear? Tt has a continuous neutral bus?
Any of the feeders, the loads, that carry a neutral from the main gear and put a load on the neutral. That's where I would try no look. Those select loads could be refed with the 480 delta to 480 Y transformer(s), to eliminate the neutral current as a load at the main MD switchgear. At the main dual source bus, eliminate the neutral connected loads, so there should be no need for the neutral conductor for any load at the MD.
The generator would be non separately derived and floating Y. The neutral would travel to the gear but the system is now 3 phase 3 wire (five conductors, neutral and EGC). Three pole switch may be possible with a solidly connected neutral.
The usual system noise of neutral current finding a parallel path on the grounding system, because of more than one system bonding jumper. Working the problem from the load side, there is no neutral current on the grounding paths, because neutral connected loads are not allowed directly downstream of the main. The main gear is 3 phase 3 wire, or can be converted to 3 ph 3 w, by converting any remaining loads than are neutral connected.
The original manufacturer of that gear, they must have a way to do it, keeping with the original functionality and design intent. There may be a way to clean up the load side and float the generator.
