Conduit size

[MarkSolar]

I'd use XHHW aluminium. It will be about half the weight and probably 30% cheaper. As mentioned it's more flexible and has tougher insulation. It's also chemical resistant if that matters in your environment.

 

[pvgirl]

I'd use XHHW aluminium. It will be about half the weight and probably 30% cheaper. As mentioned it's more flexible and has tougher insulation. It's also chemical resistant if that matters in your environment.

Switching to aluminum will require increasing the wire size to keep ampacity and voltage drop the same, 4 AWG for lines and neutral and 8 AWG for ground.

 

[Zwy]

I don't leave anything in the conduit. If I need to pull something later, I get a plastic shopping back (the kind you get at the grocery store), a kite string and a wet/dry vac.

suck the bag through the conduit with the vacuum. then tie the kite string to whatever muletape you are using to pull with, and pull it through.

It works if the conduit remains dry inside.

I'd run a heavy nylon fishing line thru it first if I was to leave the conduit empty for a long time. A piece of foam works sometimes better than a plastic bag. The fishing line won't rot like string or rope, even some mule tapes.

This past winter, there was a boring company running new wires and sleeves to upgrade the utility lines to underground. Ground foreman was out mid winter for shoulder surgery. When he was back they decided to run the wire to the distribution box by my driveway that feeds 3 different acreages.

First they put a small vac on it. Kept getting water but eventually they thought it was clear. Finally, they pulled a tape thru, then went to pull the steel cable which is used to pull the wire. Had a little problem, the tape was wet from sitting overnight and snapped. Next, they came with a bigger truck mounted vacuum and sucked for half a day. Some rocks came thru and damaged the vacuum but they did get the tape thru again and pulled the steel cable thru. Finally got the winch cranked up to pull the heavy wire.

The water came from up the hill. The distribution box was at the low spot between 2 hills and when the snow melted with some rain, a large wall of water came down the draw and filled the pipe. Along with the water it carried rocks.

 

[Bluedog225]

I appreciate that alu can work if done properly. But having ”fixed” the ex’s alu wiring, I’m not a fan. Near certain copper will outlive me.

Some beefy fishing line sounds like a good plan.

 

[wheelman55]

Like others have said 2” PVC underground and metallic above ground.

Use the long radius 90’s. They require at least a 3 ft or so depth. Super easy to pull through.

As long as you have the trench:

- bury a 6 gauge bare copper wire if you ever need to bond the grounds from conex to cabin.
- place a second conduit run a minimum of 12” inches from the first. Someday you might want to run a communication cable.
- drill holes in the bottom of the conduit if there is a water concern.
- bed the conduit runs in 4” of sand
- I bury to 4 feet depth if there will ever be any vehicles on top.

Best of luck!

 

[timselectric]

drill holes in the bottom of the conduit if there is a water concern.

I don't recommend this.
This will allow water and Mudd to enter the conduit.

 

[Bluedog225]

Thanks Wheelman. Terlingua.…the solar capital of Texas? I imagine shading isn’t much of an issue. ?

 

[CoolWill]

It works if the conduit remains dry inside.

I'd run a heavy nylon fishing line thru it first if I was to leave the conduit empty for a long time. A piece of foam works sometimes better than a plastic bag. The fishing line won't rot like string or rope, even some mule tapes.

This past winter, there was a boring company running new wires and sleeves to upgrade the utility lines to underground. Ground foreman was out mid winter for shoulder surgery. When he was back they decided to run the wire to the distribution box by my driveway that feeds 3 different acreages.

First they put a small vac on it. Kept getting water but eventually they thought it was clear. Finally, they pulled a tape thru, then went to pull the steel cable which is used to pull the wire. Had a little problem, the tape was wet from sitting overnight and snapped. Next, they came with a bigger truck mounted vacuum and sucked for half a day. Some rocks came thru and damaged the vacuum but they did get the tape thru again and pulled the steel cable thru. Finally got the winch cranked up to pull the heavy wire.

The water came from up the hill. The distribution box was at the low spot between 2 hills and when the snow melted with some rain, a large wall of water came down the draw and filled the pipe. Along with the water it carried rocks.

There is no PVC underground that doesn't have water in it. The only way I've found to keep water out of PVC is to use primer and cement.

 

[Warpspeed]

Agree, impossible to keep dry unless you are in the desert.
Water also comes from condensation as well as leakage. Think of early morning dew, and conduit does breathe, unless you continuously pressurize it with something like dry nitrogen. The telephone companies sometimes actually do that in very wet flood prone areas, not practical for us though.

The air blower and bag idea works well with new empty DRY conduit, not so well with an almost full conduit with twisted lumpy cable already in there and standing pools of water. So use the next size conduit up to what you think you need. You may be very glad later on. Do not overlook fitting a cable pit half way, especially if the conduit has to change direction along the way. The top can be completely buried as long as you very accurately measure its exact location so its easy to find later.

Fit a really strong plastic coated steel pull through at the time of initial installation, and leave it in there. It may save a lot of cussin and swearin later on.

 

[DIYrich]

I'd love to take credit for it, but it's something my dad showed me like 30 years ago. No idea where he learned it.
But, I've seen the same process used all over the place, so it's decently well known, I'd imagine

Did plastic shopping bags (today's flimsy type that could get sucked through conduit) exist 30 years ago?

 

[Warpspeed]

Some of us here are old enough to remember handkerchiefs.
A small light weight rag works just as well as plastic. Its a very old idea.

 

[n2aws]

Did plastic shopping bags (today's flimsy type that could get sucked through conduit) exist 30 years ago?

Not sure, he used to use wadded up aluminum foil. (not tightly balled up, loosely balled, and about 2/3rd the size of the conduit. I use the grocery bags, cuz they are plentiful and I always have a dozen handy.

 

[rcrracer]

Plastic bread bag with parts of bread bags stuffed inside to make it poofy. Sponge rats cost money and suck up water making them too heavy. Also the foam rats probably allow more air to slip past than bread bags do.
Funny story only slightly related. Day one: Had to run two 350' conduits for primaries and install strings for utility company. The four rigid/imc sweeps weighed 110 pounds each. First day: Heated sweeps ends with propane torch to allow female adaptors to be slid on instead of screwed. Backhoe digging, homeowners fence fell into the ditch. ran the few hundred feet of conduit, filled ditch back up , put homeowners fence back into place. Day two: Rented huge diesel air compressor trailer to blow bread bags through each of the two conduits. Slit the bottom of an empty plastic gallon size wire lube bucket. Inserted the compressor hose and bread bag and string through the slit. Turned on compressor. Jumped onto bottom bucket, held hose. Pressure built. Pressure built until I was launched about 15 feet away. Landed on my side still standing on the bucket holding the compressor hose. Problem was pipe was full of water and I didn't weigh enough. Repeated the process but added screws through bucket and into pipe. Better luck this time. Second pipe went better.

 

[timselectric]

I always use the plastic shopping bags. Like from Walmart. Tie the string to the handles and let her rip.
Works every time.

 

[wheelman55]

I don't recommend this.
This will allow water and Mudd to enter the conduit.

Tim. Our local journeyman/master electrician says that condensation gradually fills the conduit up. He recommends drilling the holes.

I can certainly see a case where the weep holes would allow dirt in and also allow roots to grow inside the conduit.

My area has virtually no vegetation so no roots to worry about.

 

[wheelman55]

Thanks Wheelman. Terlingua.…the solar capital of Texas? I imagine shading isn’t much of an issue. ?

Right, no shading. We have a “few” acres, so did a ground mount.

We have critters that will eat anything and everything. Local knowledge says that the critters can’t wrap their jaws around the 2” conduit.

 

[timselectric]

Tim. Our local journeyman/master electrician says that condensation gradually fills the conduit up. He recommends drilling the holes.

I can certainly see a case where the weep holes would allow dirt in and also allow roots to grow inside the conduit.

My area has virtually no vegetation so no roots to worry about.

The purpose of the conduit is to provide protection for the conductors. Underground conduit always has water in it. That's why the conductors have to be rated for wet conditions. Drilling holes just let's Mudd into the conduit.
The greatest benefit of conduit is the ability to change or replace the conductors, at a later date.
Not going to be easy (if at all possible) with the conduit full of dried Mudd.

 

[DVD]

The purpose of the conduit is to provide protection for the conductors. Underground conduit always has water in it. That's why the conductors have to be rated for wet conditions. Drilling holes just let's Mudd into the conduit.
The greatest benefit of conduit is the ability to change or replace the conductors, at a later date.
Not going to be easy (if at all possible) with the conduit full of dried Mudd.

I haven’t buried that much PVC conduit, maybe several hundred feet over several decades, but I’ve never had to deal with moisture inside. Interesting. Nonetheless the insulation ratings for wet environments add the insurance if the solvent joints weren’t properly connected.

 

[timselectric]

but I’ve never had to deal with moisture inside. Interesting.

It's a 50/50 shot around here.
Maybe because of elevation and the nearby Ohio River.

 

[Hedges]

?

A clarification that doesn't apply to your situation specifically. If more than 3 conductors are in a conduit then the ampacity has to be derated. In this case the Ground wire(s) is not counted.

Derating is based on current-carrying conductors. L1/N/L2/G counts as only 2, because N carries difference between L1 and L2.
(Don't tell anyone I'm capable of making it carry the sum, since I started studying PV systems and auto-transformers.)

As for conduit fill, the only way you'll reach the rated fill capacity is by stuffing wires through a straight nipple. Use WAY oversize conduit, giving yourself lots of room for this pull and the possibility of pulling more. I've gone back and pulled quite a few more 12 awg through 1.25" conduit. Always easier to pull than push, I'm not able to run fish tape through anymore. But I can use 12 awg to pull multiple 12 awg.

Stranded is easier to get around bends than solid.

Though I don’t know if a short would burn through the conductors and the pull tape.

An arc could.
Over-current shouldn't with proper size wires and OCP.

As noted, ground can be undersize for OCP protected circuits, because time is limited. This is not the case for PV runs because even if there is OCP it is sized to not trip. Ground should be sized for continuous operation.