Disconnect for PV system on detached garage

[Streetsahead]

Hello all. I'm a new journeyman after a four year apprenticeship, so I've still got plenty to learn. I've searched but haven't found anything quite like this. I've called local code enforcement but while I'm waiting for a reply I'd like to see what you all think.

What I have is a detached garage(4 ft between it and the home), for now we will assume(I haven't seen it yet) it is being powered with a uf circuit or two, so no feeder in the garage or conduit connecting, becuase the Solar contractor is quite sure we will need to use EMT between buildings. They are installing enphase panels, with built in inverters. Straight from the panels it sends 240v AC not DC out, and back feeds a 20a two-pole in the panel.

So
1) I've found nothing that states I can't run 4 feet of EMT between home and detached garage. Can someone verify?

2) I assume they will want to see a disconnect on the garage. Any reason a 2p 30a disconnect wouldn't work in this application?

3) On the previous install of this type (panels were on house roof so no detached business) the inpector let me use an irreversable crimp to connect my #6 ground from the panels/collector to the GEC in the panel going to my ground rods. Will I need new ground rods for my #6 since it's so far from the house?

 

[jaggedben]

for now we will assume(I haven't seen it yet) it is being powered with a uf circuit or two, so no feeder in the garage or conduit connecting becuase the Solar contractor is quite sure we will need to use EMT between buildings. They are installing enphase panels, with built in inverters. Straight from the panels it sends 240v AC not DC out, and back feeds a 20a two-pole in the panel.

Where to begin...

There is no code requirement to put an inverter output circuit in EMT; you can use any wiring method acceptable for a branch circuit. You just have to bond everything that's metal to the GEC that's running through it.

Normally one would dig a trench and run PVC between buildings, not EMT. At least with buildings more than 10 ft apart.

Find out if there actually aren't feeders and a panel in the garage. Because if there are, so long as the feeders to the garage are done in a code compliant manner, and both they and the panel in the garage (if there is one) have the required rating to accept a 20amp backfed breaker, there is no need to actually run the 240V circuit back to the house.

Now the ground would be a bit more complicated... see below.

1) I've found nothing that states I can't run 4 feet of EMT between home and detached garage. Can someone verify?

Hmm... Where? Overhead? Probably you are right that nothing explicitly says you can't do that. You can't put EMT underground though.

2) I assume they will want to see a disconnect on the garage. Any reason a 2p 30a disconnect wouldn't work in this application?

I'm not sure why you assume that. The code requires proper overcurrent protection wherever the interconnection is made, and readily accessible disconnecting means, and not much else. The utility may require a solar disconnect for their own reasons. For the latter, it probably should be where it is best accessible to utility personnel, regardless of which building that is on. You should ask the utility what their requirements are.

The disconnect you mention is fine.

3) On the previous install of this type (panels were on house roof so no detached business) the inpector let me use an irreversable crimp to connect my #6 ground from the panels/collector to the GEC in the panel going to my ground rods. Will I need new ground rods for my #6 since it's so far from the house?

In my opinion this is one of the most confused parts of the code, partly because 690 has changed its opinion in both the 2008 and 2011 code.

Probably the most legit way to do it (especially if you are on the 2008 code) would be to put a ground rod at the garage, and run your solar GEC to it, and also run a bonding jumper from the rod back to the house GES, and also run a separate #12 EGC from the Enphase cable to the AC groundbar wherever you are tying in. Alternatively, you could simply run a single combined GEC/EGC back to the AC groundbar at the main panel on the house, complying with everything mentioned in 690.47(C)(3), and see if your AHJ is okay with that.

 

[Streetsahead]

Where to begin...

Normally one would dig a trench and run PVC between buildings, not EMT. At least with buildings more than 10 ft apart.

Agreed. I knew I would forget a few details, namely that this is all on a slab. Underground is out, or it'd be pvc for sure. I just threw EMT into the mix because of aesthetics since it'll obviously be visible.

Feeding the garage feeder was my first idea too, but I'm just trying to be prepaired. It's a very old residence and since there is no conduit path (what I'm told) I'm assuming they didn't run a 60A feeder(or whatever) out there without a raceway.

I'm not sure why you assume that. The code requires proper overcurrent protection wherever the interconnection is made, and readily accessible disconnecting means, and not much else. The utility may require a solar disconnect for their own reasons. For the latter, it probably should be where it is best accessible to utility personnel, regardless of which building that is on. You should ask the utility what their requirements are.

The reason I assumed a disconnect would be required is because any time you feed a detached building, you need a disconnecting means on that building, right?

690.14 allows your inverter to be on the roof so long as the disconnect is visible, given the 4 listed requirements in 690.14. One being that you also have a readily accessible disconnect. The roof is not readily accessible. This becomes a grey area when you factor in enphase panels, because technically you now have your inverter on the roof. After speaking with energy trust the solar contractor was told that it's generally agreed that no disconnect is required at the enphase panels.

Thanks for your time!

 

[BillK-AZ]

Enphase wiring caution

Enphase wiring caution

You also need to be concerned about voltage rise at the inverters due to the wire resistance. If you get more than 1.5% rise to an inverter when the utility voltage is on the high side of the allowable range, the inverters will start dropping out due to a high line voltage. Most inverter manufacturers recommend that you design to 1% total rise if possible.

If you use a harness limit (M215, portrait spacing assumed) of 17 inverters per breaker and all of them are in a single long string, the voltage rise can be as high as 0.82% for the 17^th inverter, leaving only 0.78% for the rest of the wiring to the service entrance. If you have to run 50' with #10, you get another 0.82% rise and will have problems at times.

If you wire the 17 inverters as 8 and 9 in a string, the rise reduces to 0.42% in the harness.

Also, connection via remote panels may cause communication problems with the Enphase hub unless it is close to the remote panel.