Looking at a facility that wants to use an existing generator to back up a new addition that is in the planning stages. The current genset feeds a 2000 amp service, the new addition service will be 3000 amps and a new utility transformer will serve this addition. The preliminary plan from the generator and plant personnel is to replace the generator with a larger one to handle both services. Currently the existing arrangement is generator to 3 Pole SR ATS to interior switchboard. The generator company is proposing an additional 3 Pole SR ATS for the new addition, so essentially what we have is one generator set feeding two separate loads through two separate transfer switches where each load has its own utility service. Using 3 pole switches I see a 250.6 violation as there would be a solid neutral and grounding connection between the two utility transformers and their served equipment. I would think this would also introduce GFP issues on the equipment requiring it. I've suggested a 4 pole ATS for the new load would eliminate any solid link on the normal side of operations, but this would still leave a common connection on emergency operation as the existing ATS is 3 pole. I could push for replacing the existing 3 pole with a 4 pole switch but I will need some solid substantiation. Are there any other relevant articles I may be missing? Or am I overthinking this as I know pretty much every pole top transformer in any given subdivision has common connections that exist through the water mains.
Two Services/One Generator
- Thread starter ADub
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hillbilly1
Senior Member
- Location
- North Georgia mountains
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- Owner/electrical contractor
You didn’t say whether the old/and new service was ground fault protected, but if they are, you will have nuisance tripping on both if a four pole switch is not used on both.
I mentioned GFP issues in the post, 230.95 applies to both services. I am submitting for a 4 pole SR ATS for the new service, but I'm hoping to convince them to switch out the existing 3 pole with a 4 pole.
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