3 Phase 120/240 w/high leg

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Kg808

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Hello all,
I am wondering if anyone has a solution for tying into a 120/240v 3 phase system with a high leg in CA. Typically I would use a fronius Symo inverter, but these inverters are no longer Rule 21 compliant... So it seems as though I will be needing to use a transformer to step to 120/208 and use solaredge or something along those lines. However I would love to know if anyone here has tied into this type of service using an inverter without needing a transformer. Fronius has changed their compliance after the bid was made and I would love to be able to find something around the same price that doesn't use a transformer.
Thanks for the help!
 
There is no overarching reason you have to backfeed all three phases instead of using split-phase inverters on the split phase portion of the service. In fact the utility might reject either method. It's important discuss the interconnection application with the utility on these kinds of services beforehand and not make assumptions about what they will accept.
 
jaggedben said:
There is no overarching reason you have to backfeed all three phases instead of using split-phase inverters on the split phase portion of the service. In fact the utility might reject either method. It's important discuss the interconnection application with the utility on these kinds of services beforehand and not make assumptions about what they will accept.
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👍 Residential high leg services are most likely to have a much lower ampacity on the high leg, while industrial high leg services may be designed for most of the load to be three phase. But even that generalization should be checked with POCO.
 
BTW, while above comments are paramount, Enphase's IQ inverters used at 240V are feasible in theory for any number of phases on high-leg services.
 
Rule 21 is something that governs all connections of generating facilities to the grid in California.

Electric Rule 21: Generating Facility Interconnections

www.cpuc.ca.gov www.cpuc.ca.gov

Requirements have been slowly and steadily increasing for inverters to be 'smart inverters' that can respond to various grid conditions. For example power factor must automatically reduce when voltage is high or low. They are now also requiring that inverters have the capability of receiving commands from the utility to cease production and some other things. I think we are also pretty close to throttling power based on frequency. I haven't had time to follow all the details as closely as I'd like.
 
IMO it does makes sense to start having inverters that are compatible with a "smart grid". I worked on a 2.5 MW system down in Georgia 4 years ago and on the first day the solar developer's engineer was going thru the plans with everyone and pointing out some things, and he got talking about just this, having the POCO be able to use the plant for PF correction and such, pretty cool. They were using huawei inverters, and that was the first time I heard of them.
 
As said above, our MO is generally to connect to the phase without the high leg, as voltage fluctuation when connecting to the high leg is frequently an issue anyway. Granted, this is with POCO approval.
 
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