How to support underground conduit?

Status
Not open for further replies.

wus2000

Member
If some electrical conduits (suppose IMC) to be buried underground. Then how to support them, using unistut, or just laying them in the soil, or make a trench?

And for the pullbox, is there any guideline the depth of the pullbox for underground conduits. If it is too deep, then access the pullbox is difficult.
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
If some electrical conduits (suppose IMC) to be buried underground. Then how to support them, using unistut, or just laying them in the soil, or make a trench?
I would save the unistrut for another project and yes, if I were going to install these conduits underground I would dig a trench.:grin:

And for the pullbox, is there any guideline the depth of the pullbox for underground conduits. If it is too deep, then access the pullbox is difficult.
If it is too deep I agree that accessing it is difficult. :grin:

Roger
 

cadpoint

Senior Member
Location
Durham, NC
If some electrical conduits (suppose IMC) to be buried underground. Then how to support them, using unistut, or just laying them in the soil, or make a trench?

And for the pullbox, is there any guideline the depth of the pullbox for underground conduits. If it is too deep, then access the pullbox is difficult.

Why IMC underground? :) Just for giggle's I'd get the soil tested for the record have a formal document presented verses the material! Around here the struff would be eat up over time, I'm just saying.

Here's a link to one manufacture of the product. Republic.

Be sure to read all of Article 342 and note the second part of the sentence in 342.10(B).

If to be in concrete, and in the ground, why not some PVC between points? Plastic bushings are way less than grounding busings...

Depth of the run of conduit is covered in Table 300.5.

The supports that are designed to hold conduit underground piece together and interlock into a mostly plastic assemebly that I know as the term "chairs". They are staked in place, note securing in the same given Article.

I beleive the same term is used for other structural supports "chairs"; one would be used for metal rods to be held to height when the conrete is poured on it.

I also beleive there is also a true usuage of both a structural chairs in framing steel, and carpentary also, but can't think of thus right now...
 
Last edited:

kwired

Electron manager
Location
NE Nebraska
The reality is the soil around a buried conduit is what is supporting it. Now if you are looking for a temporary support until the trench is backfilled there are unlimited number of ways you could do so. If you have a lot of raceways to go in same trench you could possibly use unistrut just to help hold them in the place you want them until backfill time. If there is construction lumber scraps around I may even use those as spacers, stakes, etc to help hold things in place but once trench is filled they are not going anyplace.
 

Smart $

Esteemed Member
Location
Ohio
If some electrical conduits (suppose IMC) to be buried underground. Then how to support them, using unistut, or just laying them in the soil, or make a trench?

...
I take it then that you have never been buried in sand on the beach... :roll:
 

jeremysterling

Senior Member
Location
Austin, TX
...I beleive the same term is used for other structural supports "chairs"; one would be used for metal rods to be held to height when the conrete is poured on it.

I also beleive there is also a true usuage of both a structural chairs in framing steel, and carpentary also, but can't think of thus right now...

Thanks for the good post, cadpoint. Is the structural "chair" you are thinking of called "beam bolster"?

We have used "beam bolster with runners" to support smurf (ENT) for concrete decks. You could use it in a trench, too.

The interlocking chairs are a nice for duct banks, sometimes I use 3/4 PVC and tiewire.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
.What type of soil are you working with? How many conduits?

Most single conduits get laid into the trench after a minimal amount of leveling. Multiple may get spaced via whatever is handy. I use strut to keep the risers straight and in position if they need to be.

We had portions of a 1300' run of PVC in sand that floated up as the wind blew sand back into the ditch. That was a learning experience.

I have never buried a pull box. Always treated them as if they needed to be accessible and figured if they were buried, they were not.
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
I have never buried a pull box. Always treated them as if they needed to be accessible and figured if they were buried, they were not.

There is an exception.


314.29 Boxes, Conduit Bodies, and Handhole Enclosures to Be Accessible.

Boxes, conduit bodies, and handhole enclosures shall be installed so that the wiring contained in them can be rendered accessible without removing any part of the building or, in underground circuits, without excavating sidewalks, paving, earth, or other substance that is to be used to establish the finished grade.

Exception: Listed boxes and handhole enclosures shall be permitted where covered by gravel, light aggregate, or noncohesive granulated soil if their location is effectively identified and accessible for excavation.
 

iwire

Moderator
Staff member
Location
Massachusetts
314.29 Boxes, Conduit Bodies, and Handhole Enclosures
to Be Accessible.
Boxes, conduit bodies, and handhole
enclosures shall be installed so that the wiring contained
in them can be rendered accessible without removing
any part of the building or, in underground circuits, without
excavating sidewalks, paving, earth, or other substance that
is to be used to establish the finished grade.

Exception: Listed boxes and handhole enclosures shall be
permitted where covered by gravel, light aggregate, or noncohesive
granulated soil if their location is effectively identified
and accessible for excavation.
 

jmellc

Senior Member
Location
Durham, NC
Occupation
Facility Maintenance Tech. Licensed Electrician
I've always seen conduits laid in ditch and covered. Lots of PVC's would be in Cadpoint's chairs, plastic frames laying conduits side by side across ditch and layered up. Seems we once did 8 across and 4 high if I recall. Kept conduits roughly straight, bends aligned and stub ups plumb.

Boxes could be buried near a post or building corner, where a small sign can be posted, giving location. Or can 90 from the ground and put a box on a short 4x4 post. That's best if things may need repulling later.

I would not use IMC the whole way, unless you have to bury it shallow. Use PVC and use IMC or rigid 90's if long hard pulls. Keeps rope from cutting PVC 90's.
 

renosteinke

Senior Member
Location
NE Arkansas
I suppose it's about time we had an opportunity to discuss the very basic task of running pipe in the ground. After all, the DOL calls us "inside wiremen," so it's fair to say many have probably never run wires for any distance underground.

I'm going to give the 'gold standard,' and point out a few issues along the way ....

First off, use big pipe, and bury it deep. I say this without regard for either the type of pipe or the location of the trench.
You want 'big pipe' because pipe is cheap, digging is expensive, pulling can be a PITA, and you will love the extra room.
I say 'deep' - meaning about 2 ft. to the top of the pipe - for two reasons. The first is protection; you want the pipe to be well past the reach of the casual shovel probe or sprinkler repair. You also want to use sweep 90's to come into your handholes from beneath; this makes wire pulls so much easier.

There's a misconception about steel and rust. In my experience, once the pipe is a foot or so under the soil, the soil is packed tightly enough that there's not enough air/oxygen for rust to form. Still, I will admit that I like PVC for the horizontal runs.

If serious, or repeated, wire pulls are expected, you will want your sweeps to be steel. This is so the pull string does not cut into them. Wrap the steel in heavy vinyl 'pipe wrap tape' to prevent rust.

Just before you place the pipe in the trench, level the bottom with a layer of sand. This sand will also help prevent rocks, roots, etc., from stressing the pipe at any single point. Then put a few inches of sand over the pipe to hold it in place. If you're running more than one pipe, you might want to strap the pipe to bits of wood or scrap pipe to maintain spacing during your filling operation. Also seal your pipe ends against dirt entering; duct tape works well. Now is when you call for your 'open trench' inspection.

A proper handhole will be about 16" deep. Make little earthen 'dams' at the ends of the trenches, then fill the handhole area to this level with 'pea' gravel. The gravel will support the handhole, allow you to level it, and allow for drainage. Once you've placed the boxes, you can fill everything in. Make sure to 'tamp,' or compact, the soil around the handholes.

If your handhole is smaller than a 5-gallon bucket, you're using the wrong product. Nor are metal "Bell" boxes suitable (soil alkalinity rapidly corrodes them away, and dirt enters past the gasket no matter what you do).

It is allowed for the gardener to cover the handholes with light layers of mulch, crushed bark, etc.

Wire splices need to be absolutely waterproof, yet you need not use 'direct burial' methods. Personally, I stay away from the expensive silicone-filled wire nuts. For lighter duty applications I will simply fill ordinary wire nuts with Scotch-kote and point them so as to drain. For severe applications, I will submerge the wire nuts completely in one of the Scotch epoxy-packs (this is a product also approved for direct burial). I won't do any sealing until I am certain that the circuit is good and the connections correct.
 

readydave8

re member
Location
Clarkesville, Georgia
Occupation
electrician
I suppose it's about time we had an opportunity to discuss the very basic task of running pipe in the ground. After all, the DOL calls us "inside wiremen," so it's fair to say many have probably never run wires for any distance underground.

I'm going to give the 'gold standard,' and point out a few issues along the way ....

Also seal your pipe ends against dirt entering; duct tape works well.


good crash course! I've used many of these techniques and will try the others.

I like plumbers PVC caps stuck on dry, quicker and easier than duct tape, may not be practical in larger sizes. When I use duct tape in a place that I'll be later extending I often wrap 1st with sticky side out, easier to get off and no gummy residue. Of course any stubout left wild the taped end will be cut off anyway and I tape normally.
 

kwired

Electron manager
Location
NE Nebraska
I suppose it's about time we had an opportunity to discuss the very basic task of running pipe in the ground. After all, the DOL calls us "inside wiremen," so it's fair to say many have probably never run wires for any distance underground.

I'm going to give the 'gold standard,' and point out a few issues along the way ....

First off, use big pipe, and bury it deep. I say this without regard for either the type of pipe or the location of the trench.
You want 'big pipe' because pipe is cheap, digging is expensive, pulling can be a PITA, and you will love the extra room.
I say 'deep' - meaning about 2 ft. to the top of the pipe - for two reasons. The first is protection; you want the pipe to be well past the reach of the casual shovel probe or sprinkler repair. You also want to use sweep 90's to come into your handholes from beneath; this makes wire pulls so much easier.

There's a misconception about steel and rust. In my experience, once the pipe is a foot or so under the soil, the soil is packed tightly enough that there's not enough air/oxygen for rust to form. Still, I will admit that I like PVC for the horizontal runs.

If serious, or repeated, wire pulls are expected, you will want your sweeps to be steel. This is so the pull string does not cut into them. Wrap the steel in heavy vinyl 'pipe wrap tape' to prevent rust.

Just before you place the pipe in the trench, level the bottom with a layer of sand. This sand will also help prevent rocks, roots, etc., from stressing the pipe at any single point. Then put a few inches of sand over the pipe to hold it in place. If you're running more than one pipe, you might want to strap the pipe to bits of wood or scrap pipe to maintain spacing during your filling operation. Also seal your pipe ends against dirt entering; duct tape works well. Now is when you call for your 'open trench' inspection.

A proper handhole will be about 16" deep. Make little earthen 'dams' at the ends of the trenches, then fill the handhole area to this level with 'pea' gravel. The gravel will support the handhole, allow you to level it, and allow for drainage. Once you've placed the boxes, you can fill everything in. Make sure to 'tamp,' or compact, the soil around the handholes.

If your handhole is smaller than a 5-gallon bucket, you're using the wrong product. Nor are metal "Bell" boxes suitable (soil alkalinity rapidly corrodes them away, and dirt enters past the gasket no matter what you do).

It is allowed for the gardener to cover the handholes with light layers of mulch, crushed bark, etc.

Wire splices need to be absolutely waterproof, yet you need not use 'direct burial' methods. Personally, I stay away from the expensive silicone-filled wire nuts. For lighter duty applications I will simply fill ordinary wire nuts with Scotch-kote and point them so as to drain. For severe applications, I will submerge the wire nuts completely in one of the Scotch epoxy-packs (this is a product also approved for direct burial). I won't do any sealing until I am certain that the circuit is good and the connections correct.

For lines buried across farm cropland it is a whole different ballgame.

1400 feet plus is somewhat of a normal distance.

You better bury deeper than 2 feet or it will be damaged by farming equipment, already had to repair a couple this year that were not deep enough and got hit by ripper. About 4 foot burial is fairly normal - this allows for variations in the trench as well as some soil erosion before shallow depth becomes a problem.

There are no handholes as they will be damaged by farming equipment also.
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
Thanks for the reply. But anyone has some picture to show the real situation?

Here is an example of PVC support is sugar sand.

Lifeskillsunderground12-5012.jpg
 
Status
Not open for further replies.
Top