[RE-wrenches] 120/240 Delta

Wed Mar 25 10:53:32 PDT 2026

Jason and William are totally correct.

The question of phase angle is complicated because the phase angle is in
reference to something… if the ground is the reference, then on a 120/240
Delta, the two legs that are 120 to ground are actually 180° apart from
each other in reference to ground, But we don’t normally talk about it that
way because we normally visualize the voltage in reference to the average
voltage between the phases… and in a Y system, happens to be the same as
ground…

So even with a Victron System, you would still end up using a 180° phase
angle since you don’t have the high leg.

So yeah, any normal split phase equipment should be perfectly happy.

Thanks,
Kienan Maxfield
www.distribution.solar

On Wed, Mar 25, 2026 at 11:37 AM William Miller via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Jason is spot-on with his observation.  I completely agree.  Good work!
>
>
> William Miller
> Miller Solar.com
> 805-438-5600
> www.millersolar.com
>
>
> On Wed, Mar 25, 2026 at 10:11 AM Jason Szumlanski via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
>> You're right that all three phases of a 3-phase system are 120 degrees
>> apart. But the two conductors at this service aren't "A and C phase" in
>> that sense -- they're the two ends of the center-tapped winding in the
>> Delta transformer bank, and that's a critical distinction. The neutral is
>> tapped off the midpoint of that same winding. Two ends of the same
>> transformer winding are always 180 degrees out of phase.
>>
>> Your own measurement confirms this: two 120V phasors that are 120 degrees
>> apart produce ~208V L-L. Two at 180 degrees produce 240V. You measured 240V
>> L-L, so you've got standard split-phase (functionally identical to a 120/240
>> split-phase residential service).
>>
>> The 120-degree phase angle setting on the Quattro is for when you have
>> two actual phases from a 3-phase source (like a 208V L-L situation).
>>
>> No exotic inverter configuration needed. Any standard split-phase
>> inverter should work with this service as-is.
>>
>> Unless I'm missing something!
>>
>>
>> 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 1:03 PM Michael Morningstar <
>> mjmorningstar at gmail.com> wrote:
>>
>>> 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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