[RE-wrenches] 120/240 Delta

[Jason Szumlanski]

We do high-leg Delta commercial jobs occasionally, although I have never
done a battery backup, but it should not matter if they are only using the
two 120V legs to supply 120/240V split-phase service. The A and C legs of
120V to neutral should be 180 degrees out of phase with each other and work
fine with any split-phase inverter. Just make sure you are not using the
wild leg that is 208V to neutral, if that is even delivered to the customer
from the utility.

Most of the time, what we see is a 4-wire delivery to the customer with a
3-phase panelboard, and every third breaker space is empty. They are only
using 120V and 240V circuits. We find this in light commercial settings in
older industrial parks.

The other thing to consider is whether the utility will have an issue with
an unbalanced backfeed. FPL does not care around here as long as it's under
50kWac. They allow netmetering on two legs of a 240V delta high-leg service.

Jason Szumlanski
Principal Solar Designer | Florida Solar Design Group
NABCEP Certified Solar Professional (PVIP)
Florida State Certified Solar Contractor CVC56956
Florida Certified Electrical Contractor EC13013208


On Wed, Mar 25, 2026 at 11:54 AM Michael Morningstar via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Wrenches,
> I have a customer that has asked me to provide their restaurant with PV
> and battery back up. Easy-peasy or so I thought. It turns out that the
> service that supplies the restaurant is being fed by two phases from a
> 120/240V transformer. The service entrance conductors are direct burial and
> run under a large paved parking lot, so there's no changing that
> arrangement. I'm at a loss as what I can do here. I don't believe that
> something like a Sol-Ark 18k is going to play nice with two legs 120
> degrees out of phase? The 30K definitely needs all three phases so a 240
> Delta/208 WYE isn't going to help? I don't even think there are
> micro-inverters or string inverters available to give them just straight
> grid-tied and no BB. Are there any solutions that I'm unaware of?
> Michael
> ?
> --
>
> Michael Morningstar
>
>
> Morningstar Electric Inc
>
> PO Box 1494
>
> Mount Shasta, CA 96067
>
> 530-921-0560
>
> CSLB 1116835
>
> mjmorningstar at gmail.com
>
>
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