I have a project where they have 2 separate 240V 3phase services feeding the building. One is 200A, 3 wire, corner grounded feeding HVAC loads and the other is 400A, 4 wire, neutral grounded, high leg. They want to feed them both from a single 240V 3phase generator feeding separate transfer switches for each service. I have not run across this before and I am trying to wrap my head around how to ground these properly. Is this possible or will they need separate generators? Any help or advice is appreciated.
240V 3Ph Generator Grounding
- Thread starter ERolla95
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zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
It's not possible to both corner-ground and center-tap ground the same coil of a generator at the same time, it usually lets the magic smoke out 
. If you use two 4-pole transfer switches and interlock them, you could put the bonding jumper after the TS and leave the generator to float unless a TS is closed).
Or you could corner-ground the generator, use two transfer switches, and put a transformer after one of them to get the high-leg delta; ground that as an SDS.
. If you use two 4-pole transfer switches and interlock them, you could put the bonding jumper after the TS and leave the generator to float unless a TS is closed).Or you could corner-ground the generator, use two transfer switches, and put a transformer after one of them to get the high-leg delta; ground that as an SDS.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Kinda odd the poco built two different banks for such a small service.
Unless they used single phase panelboards on the corner grounded delta service, it would probably be the easiest to have the poco re-connect the bank to a four wire, and change the bond at the service (adding a neutral to the service disconnect)
Unless they used single phase panelboards on the corner grounded delta service, it would probably be the easiest to have the poco re-connect the bank to a four wire, and change the bond at the service (adding a neutral to the service disconnect)
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
Swap that- use a transformer to supply the corner-grounded loads, it'll be smaller.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
If the transformer is changed to a center tapped unit the entire system, it feeds, may need to be rewired.
A corner grounded system may be employing 2 pole protective and switching devices. If it was installed correctly, per code, the grounded conductor would be white
As Zbang said, connect the generator as a 4 wire delta and then provide a separate transfomer to feed the 3 wire system.
A corner grounded system may be employing 2 pole protective and switching devices. If it was installed correctly, per code, the grounded conductor would be white
As Zbang said, connect the generator as a 4 wire delta and then provide a separate transfomer to feed the 3 wire system.
drcampbell
Senior Member
- Location
- The Motor City, Michigan USA
- Occupation
- Registered Professional Engineer
When was the building wired? This was common practice during WWII, as a wartime expediency. However many contact sets you could make in a day, you could make 50% more contactors if they're only 2-pole.
If it was wired 80 years ago, it was likely with cotton-over-rubber insulation and it might be very difficult to distinguish the colors today. And that's assuming they didn't mix & match colors as another wartime expedient.
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