[RE-wrenches] 120/240 Delta

[Michael Morningstar]

David, The two phases are 120V L-N and 240 L-L. The "high leg" was not run
to the service.

Kienan, I do recall seeing a 120 degree phase angle option when I
commissioned a split phase system using Quatros. The location is in Pacific
Power territory which no longer does Net Metering so I guess it would be ok
to use a non hybrid inverter.

Maximum KW load on that service we measured 42kw. Baseline is 38kw.

Jason, I've always understood it that all phases of all three phase
configurations are 120 degrees out of phase. A=0, B=120, C=240. I'd have to
revisit my transformer theory books, but I'm pretty certain that's the case


On Wed, Mar 25, 2026 at 9:27 AM Jason Szumlanski <
jason at floridasolardesigngroup.com> wrote:

> 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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-- 

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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