3 wire service to detached building

[SPARKY1953]

I have house that receives it's service from a detached garage. The main 200 amp service starts at the garage goes through a 200 amp 120/240 disconnect is piped in pvc underground to the house with 3 4/0 xhhw to a 200 amp main breaker panel in the house the neutrals and grounds have been separated in the main panel and a #4 copper run from the equipment ground bar to 2 driven rods. The question is I want to install a automatic transfer switch just after the 200 amp disconnect and the local inspector says that I would have to replace the 3 wire to the panel with a 4 wire. This installation was installed at least 15 years ago. The only problem that I see with this would be that the neutrals and grounds had been isolated and they should have been bonded at the main panel. There is no metal connections between the buildings. The inspector (it's a small country town) insist that if I put the transfer switch in I have to replace the wire even though he sees nothing wrong with the neutrals and grounds being separated in that main panel. Am I missing something?


Thanks for the help
Sparky1953

 

[rlundsrud]

Shouldn't the neutral be bonded at the first point of disconnect (the garage) per 250.30 then the GEC would need to originate there, then a 4 wire system from the garage disconnect to the house. I honestly am not certain about this but I think that is why he is requiring it. I hope someone can clarify this further. I am also assuming that you aren't switching the neutral at your transfer switch and you are not bonding the neutral at the generator.

Bob

 

[Buck Parrish]

At one time it was permitted and common to use a three wire to additional buildings. How ever the Neutral had to be bonded to the equipment grounds.

 

[kwired]

Outside of any local rules I think NEC only requires you to run a separate neutral and EGC to the generator, to transfer switch, and any other equipment you happen to install. NEC has exception permiting an existing separate structure that was once allowed to use the grounded conductor instead of a separate EGC to remain as is, and I don't see that adding a transfer switch should change that in any way.

Kind of no different then if service equipment at the remote structure needed replaced, you wouldn't need to pull an EGC to the second structure under this exception.