Direct bury vs Conduit???

[rd65]

I have my trencher reserved for this Saturday for my ditch. What are the opinions on direct bury vs conduit? 100 amp service to shop, approx. 225' from house panel to shop. If you dirt has a lot of rocks then conduit but the holes for the building poles were very clean sandy clay type soil. 24" deep trench. Washington state so 2017 NEC regs.

 

[Aceman]

Conduit, always conduit.

PVC is cheap. There is no reason not to use it.

 

[Mr_fixit]

Conduit, always conduit.

PVC is cheap. There is no reason not to use it.

I agree, it only takes one rock to damage the insulation and ten years later it's corroded in half. And then you have to replace it again ( if you direct bury).

Around here you could have clay, sand and rock all within 50 feet.

 

[sberry]

I have thousands of feet of direct for 35 years, not one fault. The poco buries miles of entrance a year direct. If it's such a deal why don't they pipe and why isn't it code? If it's sandy it's not much a problem, it's a lot of extra work at that distance.
But it ain't there,,,,, with clay and rocks all in 50 ft.

 

[Musicinabottle]

Another nod for conduit. If ever you need to replace it, no digging required.

 

[sberry]

You would think with all the speculation there would be at least the occasional post here about failure. It seems I would have at least 1 failure if not several? One would think they would be digging up a service or 2 in my town every day from hundreds of them installed for decades. I wonder why that's not happening?

 

[Musicinabottle]

You would think with all the speculation there would be at least the occasional post here about failure. It seems I would have at least 1 failure if not several? One would think they would be digging up a service or 2 in my town every day from hundreds of them installed for decades. I wonder why that's not happening?

Me. I had to dig up my line from the pedestal to the house on account of rocky soil. direct burial. It had been buried in Sept 1982 by me when I was 16 years old, and lasted until 2004. I buried the new line in conduit swearing I'd never dig up my yard again. Much easier to pull than dig.

 

[NUTTSGT]

I'm no electrician here but the conduit gives you one more level of protection for the future.

Just ran power out to a buddy's barn (as a surprise gift) from his house. Not only did I run conduit for the power, I tossed a 3/4" conduit in the trench for any future coax, data or security system wire he may chose to run.


Compare the cost of conduit to the trencher rental. Have an issue in the future, pull the wire out and rerun it. Direct bury, rent the trencher again. Unless of course you own a means of trenching or backhoe.

 

[mike93lx]

I would run conduit too. Direct is more than likely fine, but it it is easy, why not add a little protection?

What wire are you running?

 

[alfredeneuman]

The poco buries miles of entrance a year direct. If it's such a deal why don't they pipe and why isn't it code?

The PoCo's are exempt from the NEC.
The have their own Code, the NESC (National Electrical Safety Code), written by PoCo engineers.

 

[sberry]

No kiddin? Sometimes it feels a little like spoon feeding here. The poco does this,,, past that,,, on the other end of the wire the code doesn't call for it. You would think that if this was a problem on either end one of these would give a ****. Especially the poco since they could probably get a bulk deal on some pipe? Especially with their cost of labor and long term outlook.
I will agree there are places it make a lot of sense but it doesn't need it everywhere. In this case, 225 ft, probably need to go to 2 inch to pull it, pipe it all, glue it, stick it in, now pull vs roll it out, kick it in and cover it with a little sand can be gleaned a little from the excavation.

 

[Aceman]

You would think with all the speculation there would be at least the occasional post here about failure. It seems I would have at least 1 failure if not several? One would think they would be digging up a service or 2 in my town every day from hundreds of them installed for decades. I wonder why that's not happening?

That's one point of view.

I do this for a living and we make many repairs to direct buried cables every year. And since we also work along side power companies all the time, I also know they make several repairs to their older direct buried cables too. They also use conduit now. We're starting a project right now where the customer is having their padmount transformer refed from a different direction because the DB cable has faulted and been repaired four times already.

I just checked HD's site, it looks like 2" conduit and fittings would run him somewhere around $200.

I consider that cheap in the grand scheme of things.

 

[sberry]

Yes, it adds about 200 or so, end cost is about another dollar a foot plus labor. I would say you probably are more likey to see some problems. Similar to the guy at an engine shop or my bud works on TV's. You get to see more stuff and you can be in an environment that may be different.
My Bud is in auto,,, said the other day,,, havnt ground a valve in 20 years, same for me. On common cars havnt had but 1 job had the front of an engine off and only an intake gasket in a couple of decades. My experience is likely closer to the real numbers than a guy that works at an engine replacement shop. Same reason that where every auto store used to have machine shops and almost none do now.
Come ask about it on a forum and the opin differs and likely skews away from the real numbers which likely match my own experience. I got 6 runs of direct in similar soil where I didn't chuck it full of rocks, probably 1500 ft, x 4 conductors. Never had to did it up and its been in at least 35 and although I don't wire full time have never has a call on it except for someone hitting it with equipment.

 

[sberry]

Best I can recall,,,, have never added a wire to a spare pipe, never said,,,, I wish I would have ran bigger to a light fixture cause now I wanna come back and put some 6's for a welder in it and in reality have abandoned more than added during renovation or changed route or design anyway.
Have never had to come back to upsize an air line and only had 1 water I didn't install that was marginal and mostly due to poor design. Never put 14 for lights in a house and came back to add 3 quartz fixtures where it would need a 12, not rarely but never.
This is a bit different than the design and build on a casino or large ag facility but for common folk doing common work. While codes are minimum doesn't mean its inadequate. They rate wire and pipe the same as they did 75 years ago, it all got better, voltage went up, fixtures are now low flow,, still sized the same. Buzz box welder pulls 4 less A than it did when they invent it and rate it for 220. Heck,,, poco doesn't even change a lot of the feeders from 100 to 200 upgrades anymore.
Some of this falls in to the same class as endless worry about a couple air connectors,,, what if if if if, well if it was so important the engineers would have put a 3/8 port on the new air gun if it would make any difference.

 

[readhead]

Local POCO switched to conduit about ten years ago. To many failures. I was working on a new condo development where three faults occurred before the project was done because the dirt guys didn't back fill properly. They had to dig up and install conduit and replace landscaping for 24 units.

In the pig picture why wouldn't you install conduit? It's a very small price for peace of mind.

 

[joe_padavano]

I'll be the contrarian here. I've run direct burial to four outbuildings on my farm. Some of this wire has been in place for over 20 years. I took care to bed the wire in stone dust to protect it and I was careful not to throw big rocks directly on top of the cable.

Not one issue, ever.

The only places I've used conduit is where the cable runs under a gravel road.

 

[readhead]

Nobody is saying it doesn't work. I did it at my house twenty years ago and haven't had any problems. Times change and things get done better ways. For example, carburetors work but fuel injection works better.

 

[Stuart in MN]

Direct bury will be just fine in most cases, but given the choice and the budget I'd go with conduit. Sometimes you can also get damage to direct buried cable from critters chewing on them, it's uncommon but I have seen it happen. A conduit is big enough that they have a hard time getting their jaws around it.

 

[pattenp]

Dominion Power here in Virginia has switched to using a cable-in-conduit product because of the number of repairs needing to be made to direct bury cable.

 

[b-boy]

You would think with all the speculation there would be at least the occasional post here about failure. It seems I would have at least 1 failure if not several? One would think they would be digging up a service or 2 in my town every day from hundreds of them installed for decades. I wonder why that's not happening?

The cable to my old barn had a failure. It was a 200ft run.

The power was working, then it just stopped one day. The breaker didn't even trip.

I can't say how old the cable was. Probably 15-20 yrs old I'd guess. No problems at the panel, but nothing at the other end.

 

[02vito]

I would use PVC conduit, especially if there are burrowing animals in your area. There is nothing wrong with direct-burial cable in a proper trench. Consider also the cost of wires in conduit compared with direct-bury cable.

 

[rd65]

I'm no electrician here but the conduit gives you one more level of protection for the future.

Just ran power out to a buddy's barn (as a surprise gift) from his house. Not only did I run conduit for the power, I tossed a 3/4" conduit in the trench for any future coax, data or security system wire he may chose to run.


Compare the cost of conduit to the trencher rental. Have an issue in the future, pull the wire out and rerun it. Direct bury, rent the trencher again. Unless of course you own a means of trenching or backhoe.

For me the cost of trencher vs conduit is a wash. $165 for trencher, 225' of conduit. Not that cost is my deciding factor but it does weigh in.

 

[sberry]

I am doing one this week to a pole barn, not long, 50 ft ditch in sand and its going to be direct.

 

[Musicinabottle]

That's one point of view.

I do this for a living and we make many repairs to direct buried cables every year. And since we also work along side power companies all the time, I also know they make several repairs to their older direct buried cables too. They also use conduit now. We're starting a project right now where the customer is having their padmount transformer refed from a different direction because the DB cable has faulted and been repaired four times already.

I just checked HD's site, it looks like 2" conduit and fittings would run him somewhere around $200.

I consider that cheap in the grand scheme of things.

Actually come to think about it... Northern lights did have to come out and replace their direct burial line from the pole at the edge of my 20 acres, up to the ground placed transformer. They left the old line in the ground.

 

[rd65]

I would run conduit too. Direct is more than likely fine, but it it is easy, why not add a little protection?

What wire are you running?

I don't know what to run. 225', 100 amps. Shop will not be running anything that has huge draw. Compressor is 115/230V @ 15 amps, welder is 120V @ 20 amps. Otherwise just lights and occasional grinder use. I am working with a guy (kid to me) but he is a bit hard to get ahold of and I am not overly convinced on his knowledge. Southwire voltage drop calculator says to run #1 copper or #3/0 aluminum. A guy I ran into a Platt says #2 urd w/ #4 ground in 1-1/2" conduit. This is all very new to me.

 

[rd65]

I didn't consider the underground critter factor. We do have moles and there is a rather large tree within 20-25' of trench area. Btw GopherHawk traps kick ***

 

[davidlee]

I did direct bury and had failure in about four years. I then went to conduit and that has been over ten years without and trouble.

 

[alfredeneuman]

Southwire voltage drop calculator says to run #1 copper or #3/0 aluminum. A guy I ran into a Platt says #2 urd w/ #4 ground in 1-1/2" conduit.

The guy ran into @ Platt is wrong, especially considering the length of the run.
#2 aluminum, URD or not is, rated at 90Amps.
The only time #2 is good for 100 is with service conductors, not subfeeds.

 

[LS1-IROC]

Poco just replaced our direct burial service line this spring due to a fault. Damn near burnt our house down. New service is in PVC that they had to hand trench due to access.

 

[Bert_]

I fix one or two underground faults a year. I would say 75 percent or more are caused by somebody nicking the wire when digging a post hole or something. So the falures are few.

I just had to take apart a 400 terminal box on a bin the other day. The old bin needed to be torn down and a larger one was build. Had to move the wires about 5'. Would have been a huge pain with conduit, box had 5 sets of 4/0-4/0-2/0 inside. Pulling all the wire out of hundreds of feet of conduit just to move conduit a few feet would have been much more work than just digging them up and moving the direct bury wire. Would have taken days instead of hours.

Also I can plow in direct bury wire. Can't plow conduit. I plowed in like 400' of phone line a week ago. Took maybe a half hour. I bet you couldn't even put the conduit together that fast.

 

[rburke65]

Conduit. Conduit. Conduit. And...an extra conduit. I had to redo my next door neighbors direct burial feed to his garage. 225’ is a long pull. Sweep 90*. You’ll thank me down the road.

 

[rlitman]

...Also I can plow in direct bury wire. Can't plow conduit. I plowed in like 400' of phone line a week ago. Took maybe a half hour. I bet you couldn't even put the conduit together that fast.

There are flexible HDPE conduit systems you can plow in, but I can't say that I've ever seen one used.

 

[aka Larry]

Much easier to pull than dig.

This all you need to know. Get the conduit.

 

[mike93lx]

Also I can plow in direct bury wire. Can't plow conduit. I plowed in like 400' of phone line a week ago. Took maybe a half hour. I bet you couldn't even put the conduit together that fast.

Maybe in iowa, but not in some other parts of the country. I can't dig a 12" deep hole without pulling out at least one big rock

 

[theoldwizard1]

I have thousands of feet of direct for 35 years, not one fault. The poco buries miles of entrance a year direct.

One fault on a short run. It had 2 splices because it was originally buried about 6" down ! 18" minimum. Put a caution tape about 6" above.

 

[jd_1138]

belt and suspenders -- conduit

 

[sberry]

For a small garage number 2 alum with a 50 or 60 breaker on it for 225 ft. 1.75 a foot, maybe less.

 

[RocketScott]

+1 on the conduit

All our soil is glacial till. To do direct burial you would probably need to buy a load of sand to pack around it.

While you are at it run an extra or two, even just 1"-2". I was glad I did when I wanted to run internet out to my shop. Yesterday I hooked up a hose bib on the front, really nice not having to walk back to the house for water.

 

[joe_padavano]

Nobody is saying it doesn't work. I did it at my house twenty years ago and haven't had any problems. Times change and things get done better ways. For example, carburetors work but fuel injection works better.

All my cars have carburetors. Many have points.

"New" isn't necessarily better. Why does the dome light in a car need to be controlled by the ECU? Why does a fridge or thermostat need an internet connection? Keep it simple.

 

[rd65]

+1 on the conduit

All our soil is glacial till. To do direct burial you would probably need to buy a load of sand to pack around it.

While you are at it run an extra or two, even just 1"-2". I was glad I did when I wanted to run internet out to my shop. Yesterday I hooked up a hose bib on the front, really nice not having to walk back to the house for water.

When they bored the holes for the poles there was not much if any rock. I will be running water out there for sure. 6 years of having a sink in the garage was enough to convince me to never go without water in garage again.