Anyone doing direct burial for solar DC lines from array to remote inverter?

[reader2580]

Is anyone doing direct burial for DC lines versus conduit? Code would allow me to bury USE-2 wires without conduit.

The rapid shutdown box I am looking at is set up for a 1" conduit. A 1" conduit is technically big enough for the conductors I am running, but I think it will be a pain to pull four #8s and a ground through 150+ feet of 1" conduit. I also think I could end up being over 360 degrees of bend in the conduit and need a pull box. A conduit body can be used for a pull box, but it can't be buried. I would like to avoid a giant access box in the middle of my yard just to have a conduit body accessible.

Direct burial seems so much easier other than having to be 24" deep instead of 18" deep.

[bcroe]

We managed to pull 4 number 6s and ground through 230' of straight plastic conduit, maybe 1.5". Not too hard
since there were no bends. Then the rt angles were pushed onto the ends and glued. Bruce Roe

[SunEagle]

Is anyone doing direct burial for DC lines versus conduit? Code would allow me to bury USE-2 wires without conduit.

The rapid shutdown box I am looking at is set up for a 1" conduit. A 1" conduit is technically big enough for the conductors I am running, but I think it will be a pain to pull four #8s and a ground through 150+ feet of 1" conduit. I also think I could end up being over 360 degrees of bend in the conduit and need a pull box. A conduit body can be used for a pull box, but it can't be buried. I would like to avoid a giant access box in the middle of my yard just to have a conduit body accessible.

Direct burial seems so much easier other than having to be 24" deep instead of 18" deep.

If you are running your DC lines 150+ feet between the panels and inverter, where are your panels located?

If not on a roof then I don't believe you really need a rapid shutdown box to comply with code.

[GRickard]

Four #8s and a #6 ground (all THHN) in a 1" sch. 40 PVC conduit is only 24.47% fill out of a maximum allowable 40% so conduit fill won't be a problem. Not sure why you would have so many bends in the run, embedded conduits are typically installed in as straight a run as possible with a bow in the ditch if necessary. Think of the turn radius of a trencher.

I just made a pull a couple of days ago that was eight #10s and a #6 ground, 170' with 2 90's and it wasn't any problem at all. Some people have been known to run wire then pull the conduit over it to make the pull easier. This is better than direct burial in my opinion. With the conduit, if you ever have a wire fail, you don't have to dig a whole new ditch and replace all of the wire.

Greg

[SunEagle]

Four #8s and a #6 ground (all THHN) in a 1" sch. 40 PVC conduit is only 24.47% fill out of a maximum allowable 40% so conduit fill won't be a problem. Not sure why you would have so many bends in the run, embedded conduits are typically installed in as straight a run as possible with a bow in the ditch if necessary. Think of the turn radius of a trencher.

I just made a pull a couple of days ago that was eight #10s and a #6 ground, 170' with 2 90's and it wasn't any problem at all. Some people have been known to run wire then pull the conduit over it to make the pull easier. This is better than direct burial in my opinion. With the conduit, if you ever have a wire fail, you don't have to dig a whole new ditch and replace all of the wire.

Greg

The problem with a wire that has failed and is in a conduit it being able to get it back out. I have experienced a few time that the cable shorted to the conduit and has now welded itself to the side making it very difficult to put out. The best prevention to replacing wire in conduit is to make sure the conduit is not stuffed to capacity and you have used so type of non solidifying "lube" to pull the wire through which usually helps with being able to pull the wire back out again.

[GRickard]

The problem with a wire that has failed and is in a conduit it being able to get it back out. I have experienced a few time that the cable shorted to the conduit and has now welded itself to the side making it very difficult to put out. The best prevention to replacing wire in conduit is to make sure the conduit is not stuffed to capacity and you have used so type of non solidifying "lube" to pull the wire through which usually helps with being able to pull the wire back out again.

Agreed. At 24% fill, there shouldn't be a problem as long as the conductors go in smooth and don't get all twisted and tangled. Welding wouldn't ever be a problem in PVC (if the local terrain will allow). Most likely it will never come up anyway.

Greg

[reader2580]

Array will be ground mount with inverter in garage. If the inverter is in garage then I have to have rapid shutdown because PV cables are in or on building. I had run the numbers on putting the inverter at the array and it seemed like I needed some really big wire to avoid large drops in the AC voltage. I ran the numbers again and the wire size for AC doesn't seem quite so bad. I'm still really leery about having $2000 of electronics sitting out in the rain and snow 365 days a year. One replacement inverter would pay for rapid shutdown multiple times over.

My conduit would have a 90 at each end to come out of the ground plus another 45 or 90 to go around the corner of my garage. To be fully compliant with code you are supposed to count towards the 360 degree rule any time the conduit deviates more than one degree from straight, or the trench isn't level and the grade rises or falls by more than one degree. Most inspectors aren't that stringent.

[reader2580]

I installed a standby generator last summer with 1" conduit. It was only 10 feet but had three 90 degree elbows. I was below 40% fill, but it was a royal pain to pull nine conductors through the conduit.

[GRickard]

Go to the local electrical supply house and ask for a quart bottle of "PolyWater". Pour some in the conduit and then rub a liberal amount on the wire. You'll be amazed.

A lot of the wire you get now has the "SimPull" label on it and is pretty slick without soap.

Greg

[reader2580]

I have a bottle of that stuff from when I wired my previous house in 2002. I couldn't find what I did with it when I did the generator last year. I didn't want to spend 30 minutes running to the store for another bottle as they sell it at Home Depot.

[tyab]

Simpull is amazing stuff and be aware that Southwire specifically states to not use any lube with it - the larger spools like I used have multiple huge red warning labels that you can't miss stating not to use any lube. Stuff is amazingly slippery.