Negative wire to fused disconnect

[MJSlider]

I am designing a system to DIY for my house incorporating solar, batteries, and a hybrid inverter (EG4 18kPV is what I've spec'd right now).

My utility feed comes into my basement, which is also where I want to locate the 18kPV. Per the manual I need an outdoor fused disconnect between the grid feed and the 18kPV grid input; the location for my disconnect is 75' of wire away, and the hot leads call for 3/0 AWG at that distance.

How wrong would it be to only run L1 and L2 to the disconnect switch, and just keep the Neutral and Ground in the basement running between the panel and 18kPV to save wire and effort? The neutral just runs through a busbar at the disconnect switch anyway, and I could ground the disconnect panel itself since it'd already be outside.

Like I said it would just be to save money on wire and installation effort, and it makes sense in my head but still feels kinda wrong.

So would this be dangerous, and/or would it pass code?

 

[zanydroid]

No that would not pass. EGC must go with every current carrying conductor. And it won’t be 3/0 in size anyway, so at least that goes away. Regarding the neutral, you will have objectionable EMF if only passing L1/L2, since you don’t get the cancelling effect of balanced current.

How expensive is aluminum SER anyway at this size?

The other crazy (and bad due to cost and expense, though it is safe) idea is to add an isolating transformer in the appropriate place to form neutral so the L1 and L2 are guaranteed balanced. It has to be an isolating transformer for easy code compliance. Both isolating and non isolated transformers are probably going to cost more than pulling neutral.

The outdoor disconnect requirement actually depends on your AHJ and POCO. I don’t think you are required to follow that part of manufacturer instructions. Some places let you use the existing disconnect.

Did you start the convo with AHJ and POCO?

 

[MJSlider]

Thanks for the reply, confirmed what I figured but I'd not been able to find a clear answer.

Haven't reached out to AHJ or POCO yet but I'm just about ready to start that, if I can eliminate a wire run from my basement through my garage and back that would be great!

 

[zanydroid]

OK cool.

Some places let you use the existing disconnect.

What I meant here was a breaker at your service before the panel in the basement. Current electrical code requires an outdoor disconnect, usually around the meter. I just reused that existing disconnect for my installation (with PG&E in California).