Sub panel supply side direct line taps

[keaton85]

I have a 200a main disconnect at my meter going to my house which is a 200a sub panel. To avoid 120% rule and to allow for easier generator install, I would like to line side tap for the inverter. Code 705.11 does state it is allowed for 6awg copper yet this still doesn’t make me feel great having that size on a 200a breaker.

thoughts? I could drop down to a 175a main breaker for the sub panel, yet I’m stuck with my generator being on this same panel which complicates things.

[solarix]

Not clear on what exactly you mean. What size is your inverter? A line side tap would require a service disconnect wired to the line side of the meter. This is could be a problem as technically, the panel you have would need to be "listed'" for such a modification. (although most AHJs won't make a fuss about that) The disconnect would have to be service rated (22,000AIC), have fuses for what ampacity you want, and rigid conduit used. Plus you need a permit to do a line-side tap as the utility will have to de-energize your service to do the work.

[keaton85]

The system would be around 9.6kw of initial paneling with a 10kw GTI, 42a is the rating for the inverter. Line tapped on the sub panel side so the initial service disconnect would allow for this without removal of the meter. I have a QO panel with conduit run out to the inverter location

AHJ wouldn’t understand any of this, I could pass with pretty much anything that looks correct.

[solarix]

I suggest splitting your array into two orientations (at least 90 deg different) and using a 7.7kW inverter. With two orientations, the array will never put out more than 7.7kW and the inverter's 32A current rating will not exceed the ampacity of a 40A backfed breaker and you can meet the 20% backfeed rule with a simple load side interconnect point.

[keaton85]

I only have one south slope and no other location. I built the house just for the orientation.

I could just do a 175a breaker and that frees me up, yet I would want to do a contractor on the solar feed so when gen is online it would release the solar feed. This is where the line side tap helps.

[keaton85]

The inverter is rated at 42a output, so I’m assuming I could do a 45a breaker

[solarix]

Solar is classified as a continuous load so the wire ampacity has to be 125% of the max inverter output. 42A x 1.25 = 52.5A so a 60A breaker on #6 wire is needed. Reducing the main breaker to 175A gives you 25 + 40 = 65A of allowable backfeed. The inverter will trip off if it sees a generator for a load, but disconnecting it would be wise.

[oregon_phil]

From the SE manual

[keaton85]

Solar is classified as a continuous load so the wire ampacity has to be 125% of the max inverter output. 42A x 1.25 = 52.5A so a 60A breaker on #6 wire is needed. Reducing the main breaker to 175A gives you 25 + 40 = 65A of allowable backfeed. The inverter will trip off if it sees a generator for a load, but disconnecting it would be wise.

Thanks! I forgot about the 125%, was going off 120%, yet that doesnt even work for the 42a to 45a breaker.

So to through another curveball into the mix, this sub panel is fed off the "main" panel which has another 200A breaker, so change the main breaker to 175A, just the sub panel to 175A or both! since the main panel could technically receive the "60A" continuous current.