New 4.6Kw PV on barn with existing UG 6/2 feed to house main.

[DaneD]

Running into an issue with the AHJ over a pre-existing UG feed in PVC. Our customer has a barn with a 60A sub panel with a 6/2 UG wire feed through 100 feet of 1 1/2" PVC conduit back to the house main (40A breaker), sub panel has neutral/ground bond. Our design is to remove the 6/2 UG wire from the conduit and run 4 XHHW-2 6 AWG aluminum cable feed from the main panel to the sub panel in the barn, remove the bond in the sub panel, and add a GEC at the barn. Sounds reasonable right? AHJ agreed to this part of the solution.

The new 4.6 Kw PV system will be a 12 panel array with Enphase micros split into 2 strings. This requires 4 more 12G copper XHHW-2 wires for the 2 strings, plus an additional 12G copper XHHW-2 wire for the PV system ground. So in total, the 1 1/2" conduit will have four 6 AWG and five 12 AWG wires. There will be a junction box on the exterior of the house where the wiring will be separated, solar to the Enphase combiner and the 4 #6 wires into the house to the main for the barn power. The junction box will have continuous feeds, this is only to separate the 2 sources appropratly.

We have done similar configurations in the same jurisdiction in the past without any issues, however the new AHJ is refusing to sign off on this citing that 2 different power sources cannot be enclosed in the same PVC. I can't find anything in our code saying this is not allowed. Homeowner does not want to dig up the sod for an additional PVC run. Is there something in the NEC I am mising? The AHJ isn't providing any specific code that does not allow this.

 

[wwhitney]

Why run the PV output conductors back to the main panel at all, why not just utilize the existing feeder and interconnect in the existing subpanel (after removing the improper neutral-ground bond and installing the required GES)?

Cheers, Wayne

 

[jaggedben]

AHJ is wrong. They may be thinking of 225.30 but see 225.30(A)(5).

I gather that you want to run the solar back to the house because there is also solar on the house and you want the combiner there. I would probably use 8awg for that distance and split the circuit with a separate subpanel at the bar. If it's just grid tied solar, Wayne's idea may also work.

 

[DaneD]

Why run the PV output conductors back to the main panel at all, why not just utilize the existing feeder and interconnect in the existing subpanel (after removing the improper neutral-ground bond and installing the required GES)?

Cheers, Wayne

Valid question, I agree. The homeowner has three requiremnets.
1. The combiner needs to be on the house for future PV expansion strings on the house roof.
2. Accurate PV production and grid consumption monitoring, one reason they are paying extra for Enphase.
3. Future battery backup using the Enphase controller mounted in the basement of the house near the main.

I can understand their requirements. It seems with all of that, the best or only solution is to keep the barn feed and PV production separate.

Thank You for replying!

Cheers!

 

[DaneD]

AHJ is wrong. They may be thinking of 225.30 but see 225.30(A)(5).

I gather that you want to run the solar back to the house because there is also solar on the house and you want the combiner there. I would probably use 8awg for that distance and split the circuit with a separate subpanel at the bar. If it's just grid tied solar, Wayne's idea may also work.

Yes, there may be an expansion on the house roof, or more likely on a carport adjacent to the house. Battery backup for critical circuits is also on the near future.

I'll review those code sections and see if I can come up with a convincing response to the AHJ. New guy, young and seems to enjoy weilding his sword of power over us ;-)

Thanks!

 

[winnie]

1) Can/should the PV system EGC be _separate_ from the barn feeder EGC?
2) Even if you get over the 225.30 restrictions (which seems plausible to me since the solar DC circuit clearly has different characteristics from the 120/240V AC circuit), don't you still have a problem with having two solar circuits going between the structures?
3) Assuming you overcome all 225.30 restrictions, don't you now have 6 current carrying conductors in the single conduit, triggering derating?

-Jonathan

 

[wwhitney]

Valid question, I agree. The homeowner has three requiremnets.
1. The combiner needs to be on the house for future PV expansion strings on the house roof.

If I understand correctly, there would be no problem having separate arrays on the barn roof and the house roof, with each using its own combiner. Certainly each building will need its own rapid shutdown initiator, and there's no particular reason for the rapid shutdown initiator for the house to shut down the PV on the barn.

2. Accurate PV production and grid consumption monitoring, one reason they are paying extra for Enphase.

The barn would need a network connection for the Envoy in the barn for the barn array. Unless the PLC (power line communications) from the microinverters will work over the distance from the barn to the main house, allowing the Envoy to be in the main house. I can imagine in that scenario that if the distance is marginal, putting the microinverters on their own feeder could improve the PLC vs having them on a shared feeder with the barn loads. But I'm not seeing the upside to pulling two separate 20A microinverter circuits, vs combining them into a single 40A circuit from house to barn.

3. Future battery backup using the Enphase controller mounted in the basement of the house near the main.

That would be an issue if the barn has loads that are not to backed up. In which case, I agree you need two feeders to the barn, one backed up (the barn PV could be on that one if 2 is not an issue) and one not backed up.

Cheers, Wayne

 

[DaneD]

1) Can/should the PV system EGC be _separate_ from the barn feeder EGC?
2) Even if you get over the 225.30 restrictions (which seems plausible to me since the solar DC circuit clearly has different characteristics from the 120/240V AC circuit), don't you still have a problem with having two solar circuits going between the structures?
3) Assuming you overcome all 225.30 restrictions, don't you now have 6 current carrying conductors in the single conduit, triggering derating?

-Jonathan

Hmm, I never considered #1 and the AHJ never mentioned it either. I do know that Enphase states that a continuous or uninterupted ground is required from each string mounting hardware all the way back to the combiner which will be on the exterior of the house. We have never combined that with the outbuilding feeder ground. If we are doing that wrong, no AHJ has said anything about it.

The Enphase microinverters supply AC voltage from the back of each panel. Each string in the combiner can only be 20A. So in this scenario, the IQ8HC can prode a max of 380w. Our design is to have 9 (15A) panels on string 1 and 3 (4.25A) panels on string 2. This is where we need two 12G strings running to the combiner. Theoretically the HO could add another 6 panels to string 2 on the barn with roof modifications, thus we leave string 2 wiring at 12G.

It is common for Enphase installations to run 4 strings (4 sets of 12G XHHW-2 wire) all in single conduit. That is four separate (8 current carrying conductors) power sources in on PVC.

Hoping that previously mentione 225.30(A)(5) will solve my AHJ issue, it seems pretty clear.

Thanks!

 

[winnie]

It is common for Enphase installations to run 4 strings (4 sets of 12G XHHW-2 wire) all in single conduit. That is four separate (8 current carrying conductors) power sources in on PVC.

There is no explicit limit to the number of current carrying conductors in a conduit. However when you have more than 3 CCCs 'derating' kicks in; the maximum allowed current on any conductor is reduced.

This generally isn't a problem for 12ga circuits, because there are multiple rules limiting maximum current, so you don't 'see' derating for up to 9 conductors. But the derating rules might be a problem for the barn feeder. With 6 CCC, the ampacity of 6 awg Al conductors is reduced to 48A. If derating is the problem, then you might need to go with Cu conductors or 4 awg if you can fit them. (I've not done the conduit fill calculation).

 

[jaggedben]

There's no PV DC circuit here, it's micro-inverters so it's AC from the barn.

It's industry standard to upsize solar conductors for less voltage drop, and that would take care of any derating concerns for the solar. I agree that going up to 4awg for the barn power might be a good idea, depending on the load. None of this will be an NEC conduit fill violation. I would still combine the (2) solar circuits to the barn into one, for an easier wire pull and to not appear to be overdoing it on the 225.30 allowance.

Enphase power line communications should be fine at the distance mentioned. There is no need for an Envoy at the barn.

In other words, it really would be good and perhaps best if the AHJ can get over their unsupported objection.

 

[DaneD]

I can go with 4G on the barn circuit, it will cost about $30 more.
As for combining the 2 PV circuits, how would I properly "uncombine" them in the combiner? The Enphase 5C combiner has four 20A circuits. With the 12 panel array providing a max of 20A, I can understand it may be OK, but if they do add 6 more panels, then there will up to 30A. This needs to be a near perfect split back into two separate circuits evenly balanced in the combiner. We have always run individual strings from the PV array to the combiner, but I'm all for making life easier.

I have another question I'll create a new thread for. We usually chose the panels based on the best physical fit for the roof. Most cases the roof is large enough where it doesn't matter as long as the panel voltage is at least 40V, but in this case we went with Jinko 425W panels 12 fit on the roof perfectly. We never used this panel before and I just noticed they have a max of 32V. I'm concerned that on hazy days or a little shading will drop the voltage too low for the microinverters to work. Although the Enphase compatibility calculater say that the IQ8-HC is good. Maybe I'm overthinking this one.

Thanks everyone for your help. I have a meeting with the AHJ tomorrow morning on site. Hopefully he relaxes his position a bit.

 

[jaggedben]

You don't have to 'uncombine' the micro circuits in the combiner. Just put them on a single 25A or 30A breaker. The combiner is fine as long as total output doesn't exceed 64A on 80A worth of breakers. For example Enphase supports putting an Enphase Aggregator on a 60A breaker. (It's OOP but they still support it.)

(I assume you're using IQ8As or some such micro that requires more than one 20A circuit in the first place.)