120 Volt Supply side connection with single Outback Power VFXR

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ACDCBag420

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Location
Rutlant Vermont
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Solar
Having trouble understanding the balancing issues with connecting a 120 volt inverter supply side. The house has a 100 amp service with type SEU cable as feeders. My options for ac interconnection are to either go line or load side. One option it to swap the panel out for a 125 amp panel with a 100 amp main breaker. This larger panel would allow me to backfeed my 30 amps through a breaker in compliance with the code. My other option would be to go supply side which I would have no problem with if it were a 240 volt supply from the inverter. Wanted to get some opinions on this cause I have heard mixed things from different licensed electricians when it comes to making a 120 volt supply side connection on a leg and the neutral. Really dont want to swap the panel because of cost and time.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
While I have never heard of it being done, there would be no meaningful code or physical difference in connecting a 120V inverter supply side, as compared to a 240V inverter. Go ahead and do it if you want.
 

ACDCBag420

Member
Location
Rutlant Vermont
Occupation
Solar
So a caviat to this is that the inverter can either backfeed 30 amps in grid tie operation, but it can also pull 60 amps to charge batteries and power the critical load sub panel. If the supply side tap was drawing 60 amps would that cause the 100 amp main to trip if their was a demand for 40 amps on the bus, or would there still need to bee over a hundred amp draw on the bus to trip the breaker, basically I guess what im asking is will I overload this wire if the feeder tap is pulling 60 amps?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
If there is a 100A breaker ahead of where you're connecting then it's not a supply side connection, by definition. So are you talking about a feeder tap?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
See 705.12(B)(2)(1) (2017 NEC reference) for rules for connecting to feeder taps.

You need to do a load calculation to determine if the feeder can handle and additional 60A. I'm not optimistic.
 

ACDCBag420

Member
Location
Rutlant Vermont
Occupation
Solar
The feeder is not coming from a panel its coming from the utility transformer. The service wires are 1 awg USE aluminum feeding a 100 amp main breaker. I think my understanding of a tap vrs a feeder is a bit skewed, but yes it would be a line side connection tapping into the feeders of the service. Either way I found out the bus on the panel is rated for 125 amp so I can back feed my thirty no problem through a breaker. thanks for the responce, I still need to refrence the code more to get a better understanding of what a feeder is vrs a tap.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Read article 100 definitions for service conductors, feeders, and branch circuits. Conductors between the service point and the service disconnecting means are service conductors, not feeders. And and that's where supply side connections are made.
 
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