Need conduit/trenching planning advice

[Fallon]

I'm going to be running 3 conduits from the house out to the end of my driveway. 1 power (20@ circuit), 1 for fiber, & one because conduit is cheap & trenches are expensive. Total run is about 350'. I've got several 100' chunks & 50' chunks glued up already & laying next to the driveway. I've got a 3pt trencher for my tractor that cuts a 6" trench up to about 3' deep (not quite enough to clear the frost line here in Colorado).

I don't expect more than 3@ normal use tops, probably less, occasionally using 10-15@ a few times a year for HAM radio field day out in the pasture or an occasional power tool. Debating between 12 & 10 gauge, possibly 8 to fight voltage drop. Shouldn't be a big deal at the average amp or 2 of draw going into regulated 12v power supplies (for that matter most of my higher amp usages will be HAM radio field day, also into regulated 13.5v power supplies). But I'll figure that out at some point after the conduit is all installed.

East side option: Pretty much a straight run for 350', except for the sweep 90's at each end.
West side option: Not quite as straight, but I have a spot for a pull box 100' from the house & would end up putting in a 30-40' chunk of drain pipe in the same trench in under a driveway to later pull some drip line in.

In either case I'm likely dropping in 2 30' conduits to go under the driveway right next to the arch & another down the side driveway on the outbound drivers side to put a button on a post for an eventual gate opener.

Where is a good cheap source for a pull box? Don't see any listed at Home Depot/Lowes & I assume the $30 plastic sprinkler ones aren't rated or appropriate for electrical.

Red = new conduit I need to put in
Blue = 3-4" conduit I'd put in if I went that way (would terminate next to the pull box, not in the pull box)
Green = pull box
Pink = existing 16" culvert
Yellow = 6" small culvert I'd likely put in

West side route East side route

Ranch arch at the end of the driveway

 

[leonz]

Hello Fallon,

Have you considered just using the 90 degree sweep to pull the cable through and simply having a splice box above the ground which is how it is done as a rule??

I do not think your going to find an inexpensive water proof cable splicing box as you will have to rent a winch to pull the cable through the conduit after you snake the nylon twine and then the winch rope from one end to the other. you will also have to invest in a couple of kellums clamps to pull the cable through.

Your going to have to rent or buy a tape snake to run the nylon twine through the conduit and then the winch rope and then the cable. your also going to have to buy a pail of cable lube to prevent the cable skin from being damaged and increasing the friction on the cable when pulling it through the conduit.

Some contractors also use a shop vac to pull a pipeline pig ball through the conduit that is also carrying the nylon twine to start the process.

 

[TemporaryKubotaOwnerMark]

Your going to have to rent or buy a tape snake to run the nylon twine through the conduit and .

Not if you run the twine or rope while you are gluing it. It's easy to tie a weight to the end of it and just drop it through the section, glue it up, repeat.


But, he's already got long sections glued up, so the easy way isn't an option for him.

 

[Redlands Okie]

And leave a pull rope in that spare conduit........

 

[Fallon]

Hello Fallon,

Have you considered just using the 90 degree sweep to pull the cable through and simply having a splice box above the ground which is how it is done as a rule??

I do not think your going to find an inexpensive water proof cable splicing box as you will have to rent a winch to pull the cable through the conduit after you snake the nylon twine and then the winch rope from one end to the other. you will also have to invest in a couple of kellums clamps to pull the cable through.

Your going to have to rent or buy a tape snake to run the nylon twine through the conduit and then the winch rope and then the cable. your also going to have to buy a pail of cable lube to prevent the cable skin from being damaged and increasing the friction on the cable when pulling it through the conduit.

Some contractors also use a shop vac to pull a pipeline pig ball through the conduit that is also carrying the nylon twine to start the process.

I've successfully sucked or blown a plastic bag through a couple hundred feet of conduit before with an air compressor or shop vac. In theory a perfect vacuum is around 15psi below atmospheric pressure, so blowing with 100psi air ends up driving the pull string & parachute through better than sucking. Have a 5 gallon bucket full of pull string as well. While I haven't done it personally I know of a good number of people who have glued conduit around pull string before. They then get to pull a new pull string through because the first one ends up glued to the conduit in several places inside.

I wasn't assuming the pull box was going to be waterproof. I have a concrete one up near the shop that the guys installing my solar put in (right in front of the shop before the trench makes a 90 degree turn). It's just sweep 90's coming up through the dirt inside the box. I haven't busted it yet driving over it with the tractor, but pretty sure I would if I didn't have it flagged, so don't want another one out in the middle of the field or my driveway. Cable comes in one pipe, does a 180 & goes back down the next pipe, no splicing. It's just there so you are only pulling half the conduit at a time. I could probably just use a sprinkler box for that, but figure I should try & do it right if it's not going to be to costly.

I'm more worried about the cable pull lengths than anything else. Some of the pulls around 100' in the back yard were pretty squirly to pull as they had a little over to 360 degrees of bends in them despite not being that long. These runs are going to be longer, but pretty straight, so wondering if I should bother with a pull box where it would fit reasonably well 100' out from the house near a tree. All the other spots to put a pull box are likely to get damaged from being driven over when mowing, or would be under the outlet of a culvert (which would flood the conduit & box with mud & water).

Amusingly Google maps still shows all the trenches open all over the back & side yard from a year and a half ago when I dug them for the solar install (trenched out to the chicken coop to install power & put in a couple frost free water hydrants while I had the trenches open too). Google Maps

 

[RNeumann]

Run the conduit at the recommended/code depth. Electrical at 2', water 6"-12" below frost line (deeper a the driveway) and fiber at 12-18". Technically they can't be in the same trench so separating them vertically will help. I now fiber doesn't suffer from being next to an electrical line but copper data can degrade so separate those two as much as possible- opposite sides of trench and depth difference.

Your local electrical wholesaler will have a pull box. I'd go for 10ga wire. You are correct to upsize for voltage loss. But 8ga doesn't hook to plugs etc well. Plus, in a pinch the 10ga can run most RVs.
As far as pull cord just put the conduit in and put the string in later. The old vacuum/leaf blower/BIG air compressor and plastic bag trick is what folks who do this everyday use.
This is a poor homeowner type video but you get the idea-
vaccuming a string through a pipe - YouTube

You will need to size the conduit. If the utility will be running the fiber (their box is at the house) they will demand a specific size. Most will require something way to big. If it's on your side of the utility (box at road) then an 1 1-4" or bigger should do. The electrical should be sized for 3-4 10ga THHN wires-4 wires (only one extra) would give you 2 20-30a circuits- a little extra for your HAM stuff at little extra cost. They have conduit sizing calculators. Southwire has one on their website or let me know and I can do it.
Take your time and cut the ends straight, debur and glue properly. The last thing you want to do is have to dig something up because you rushed. Same goes for keeping debris out- lift and pull pieces to you- no pushing conduit away from you!
You will also want long sweeps- spend the extra few bucks. The wholesaler will have the nice ones- their is a difference.
The extra one should be over and inch imho. No reason to underside that one.
350' technically doesn't need a pull box. However I'd leave a 20' section in the middle exposed until you get the pull cord through- just in case.
If you hadn't purchased conduit already I'd recommend going to HDPE. With a tractor you could get spools and do it in one shot. However, regular PVC will work fine.

Good luck and keep us posted. It's always nice to help folks who want to do things right!

 

[lennyzx11]

I've successfully sucked or blown a plastic bag through a couple hundred feet of conduit before with an air compressor or shop vac. In theory a perfect vacuum is around 15psi below atmospheric pressure, so blowing with 100psi air ends up driving the pull string & parachute through better than sucking. Have a 5 gallon bucket full of pull string as well. While I haven't done it personally I know of a good number of people who have glued conduit around pull string before. They then get to pull a new pull string through because the first one ends up glued to the conduit in several places inside.

I wasn't assuming the pull box was going to be waterproof. I have a concrete one up near the shop that the guys installing my solar put in (right in front of the shop before the trench makes a 90 degree turn). It's just sweep 90's coming up through the dirt inside the box. I haven't busted it yet driving over it with the tractor, but pretty sure I would if I didn't have it flagged, so don't want another one out in the middle of the field or my driveway. Cable comes in one pipe, does a 180 & goes back down the next pipe, no splicing. It's just there so you are only pulling half the conduit at a time. I could probably just use a sprinkler box for that, but figure I should try & do it right if it's not going to be to costly.

I'm more worried about the cable pull lengths than anything else. Some of the pulls around 100' in the back yard were pretty squirly to pull as they had a little over to 360 degrees of bends in them despite not being that long. These runs are going to be longer, but pretty straight, so wondering if I should bother with a pull box where it would fit reasonably well 100' out from the house near a tree. All the other spots to put a pull box are likely to get damaged from being driven over when mowing, or would be under the outlet of a culvert (which would flood the conduit & box with mud & water).

Amusingly Google maps still shows all the trenches open all over the back & side yard from a year and a half ago when I dug them for the solar install (trenched out to the chicken coop to install power & put in a couple frost free water hydrants while I had the trenches open too). Google Maps

Just laid two two inch conduits 24 inches apart and 24 inches deep. One for water and other for electric.
Used a nylon string from the trotline fishing section of Walmart and the plastic bag it came in with my 8 year old shop vac.
Turned on shop vac at one end.
Shoved bag into other end (120 ft) with string tied to handles.
Walked to shop vac end where bag was waiting. I had 2 45 degrees and on 90 upright sweep for it to pull through.

 

[2458n]

Directional boring is another method of doing this.. Guys who do it all week long use their bosses machine on Saturday to pick up some pocket change.

 

[Fallon]

Directional boring is another method of doing this.. Guys who do it all week long use their bosses machine on Saturday to pick up some pocket change.

I already bought the 3pt trencher for this & a few other projects. Spent the last weekend helping a friend dig a similar shorter trench for a similar project.

 

[tmc_31]

Fallon, a couple of things to think about. Assuming that you want to stay within the 3% voltage drop limit (per NEC), 4 amps is about all you can count on if you use #10 copper wire. If you up size to #8, you can count on about 7 amps being available.

You don't say what size conduit you are using, that needs to be determined based on the number and size of conductors you are using.

I was in the business of installing sports lighting systems for many years so I am no stranger to pulling wire for long distances. The longest pull I ever made was just over 900' with 3-#2's and 1-#4 conductors in a 2" conduit. We used my tractor to pull the well lubed wire. I would suggest that you leave the 90 deg sweeps off until the pull is done then add them after. This helps keep the pull as straight as possible. Also, if you use a nylon pull string the string will cut through the wall of the sweep and of course the string will break at that point. I think there are other string materials that are less likely to have this problem but I can't remember what they are offhand. I always used the shop vac method of pulling my string through the conduit (even on the 900' run it worked just fine).

One more point then I will leave you alone. If you soil is rocky, consider bedding your conduit in sand. This means at least 4" of sand below the conduit and 8" above it. The conduit must also be centered in the ditch so that you have at least a conduit diameters width between the ditch sidewall and the side of the conduit on either side of the conduit. If you cut a 6" wide ditch it should be sufficient for 2" conduit.

All the best,
Tim