single phase inverter in a residential 3 phase, 120/240VAC, DELTA, panel

[ggunn]

Main says
"240/120V, 3phase 4 wire Delta"
"208Y/120V, 3ph4wire"
400A rated service.

Understand that the labeling says what the equipment is rated for, not what the service actually is. For example, I got burned early on in my experience when I read the rating on a main MDP switch that said 480V when the service was actually 208V. From the switch labeling I thought it was a 480V service and I designed a system accordingly. I fixed it but it was an expensive learning experience.

What doesn't kill you makes you stronger.

 

[Smart $]

SmartMoney,
I can see two transformers up on the pole.

You have an open delta supply. The other guys have steered you correctly on matters where this affects performance and compliance. Providing your inverter is capable of being connected 240V L-L w/o N, in theory you could connect to any L-L pair, but connection between the "open" line pair would exhibit the worst performance in the real world.

 

[Zee]

Jaggedben,
Exactly, I do not see any single phase loads connected to the B phase.
Yes I will connect A-C.
Inv.: sma sb3800tl-us

I have found this Delta configuration with a high leg of 208V quite common here in PG&E territory. Just for my edification would this high leg be called a "stinger"? I wonder if this term is very local or in common usage.

Ggunn and Jaggedben,
I should have realized that the generic factory provided label on the main service isn't necessarily how the panel is wired. Excellent point and thank you!

Ggunn,
Ouch! Designing for wrong grid voltage is bad enough I hope you didn't also buy the equipment! Been there I feel your pain.

GoldDigger,
Yes I agree that if I connected across any of the phases that included the B leg of 208 volts it would screw up the inverter which is trying to balance the 120 volts to neutral.

SmartMoney,
just for future reference I am a little bit knowledgeable about open Delta but I think what I have is called, or could be described, as a center SIDE tapped Delta. An equilateral triangle with the neutral on one of the three sides ....midway between points A & C.

I don't know if in an open delta configuration of 240V any of the phases would be 120 V to ground?

 

[Zee]

Thanks all! Very helpful.

 

[GoldDigger]

Jaggedben,
Exactly, I do not see any single phase loads connected to the B phase.
Yes I will connect A-C.
Inv.: sma sb3800tl-us

I have found this Delta configuration with a high leg of 208V quite common here in PG&E territory. Just for my edification would this high leg be called a "stinger"? I wonder if this term is very local or in common usage.

Ggunn and Jaggedben,
I should have realized that the generic factory provided label on the main service isn't necessarily how the panel is wired. Excellent point and thank you!

Ggunn,
Ouch! Designing for wrong grid voltage is bad enough I hope you didn't also buy the equipment! Been there I feel your pain.

GoldDigger,
Yes I agree that if I connected across any of the phases that included the B leg of 208 volts it would screw up the inverter which is trying to balance the 120 volts to neutral.

SmartMoney,
just for future reference I am a little bit knowledgeable about open Delta but I think what I have is called, or could be described, as a center SIDE tapped Delta. An equilateral triangle with the neutral on one of the three sides ....midway between points A & C.

I don't know if in an open delta configuration of 240V any of the phases would be 120 V to ground?

The designation of open delta refers entirely to the fact that there are only two transformers connected to the three ungrounded wires. This gives you three voltages in an open triangle. If A-B is the open side any line to line load connected there will get the correct voltage and phase, but the change in voltage with change in load current (load regulation) will be at larger than on the other two phases.
The center tapping of one winding for use as the grounded neutral for 120/240 loads is independent of whether the delta is open or closed.
As a historic development, high leg was often used in a situation where the three phase load was small compared to the single phase load, and that same situation was also a good candidate for an open delta source.

 

[Smart $]

...
SmartMoney,
just for future reference I am a little bit knowledgeable about open Delta but I think what I have is called, or could be described, as a center SIDE tapped Delta. An equilateral triangle with the neutral on one of the three sides ....midway between points A & C.

I don't know if in an open delta configuration of 240V any of the phases would be 120 V to ground?

As GD explained, the winding center tap giving you two legs of 120V to a grounded center-tap conductor is independent of being an open or closed delta system. Obviously you can't tap the "open" phase... so whichever of two secondary windings is tapped (and grounded), the ends become lines A and C at distribution equipment under NEC purview.

 

[Zee]

Great information. I see now how the terms open Delta and the 208v high leg 120 / 240 system I have is compatible. I was just trying to be a hundred percent certain on this job that everything is kosher. I see a slash rated 120 / 240 Breaker across the A & C legs, existing. I will be plugging on my 2p20A, slash rated breaker across the same legs.....the same way. Ensuring 120v to ground and avoiding the 208v.
Thanks again.