# Quick question about underground PVC install



## MikeFL (Apr 16, 2016)

Pipe is 2-3' u/g in a region with a 5' frost line.
It's going to move.
I'd think vertical expansion joint is sufficient, but my inspections tenure is limited to working in beach sand where we don't have freezing.
Let's see what the peers up north say their inspectors expect.


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## J F Go (Mar 1, 2014)

I have never used expansion joints underground. Where it is above ground is where it is required. That is where thermal expansion will occur. The NEC says " at the start of a run" but I always do it at each end if it is outside and in the elements at both ends. Nothing in the NEC says anything about using them underground that I could find. Make him show you where it's at because you have looked and can't find it.


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## tmessner (Apr 1, 2013)

Sure the ground moves. In every direction under the sun. The expansion cplg will not work in the the ground as it will be held in place by the frozen ground. They only work poorly above ground once the real world has deposited enough dust and crud o them.


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## Southeast Power (Jan 18, 2009)

Vertical, yes. Underground? You have to hold the barrel in place for it to work.
Maybe you Yankees have some kind of underground type. We don't see those here.


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## HertzHound (Jan 22, 2019)

Are you sure you understood the inspector? Expansion joints direct buried is unheard of to me. 

Years ago we never worried about expansion joints where it emerged from underground. Today the inspectors would require it. I think that’s what your inspector meant. I would have found a way to use an expansion joint where it emerged from grade. If that meant using an LB going inside, instead of a sweep, that’s what I would have done. I don’t think I ever stubbed up into a sweep going into the building anyhow. You would need an expansion just going up a few feet into a meter pan around here. I have seen PVC pulled free of the connectors in the past. With such short runs I wouldn’t think it was expanding in the PVC, but Earth settling. 



> 300.5 (J)
> (J)Earth Movement.
> Where direct-buried conductors, raceways, or cables are subject to movement by settlement or frost, direct-buried conductors, raceways, or cables shall be arranged so as to prevent damage to the enclosed conductors or to equipment connected to the raceways.
> Informational Note: This section recognizes “S” loops in underground direct burial cables and conductors to raceway transitions, expansion fittings in raceway risers to fixed equipment, and, generally, the provision of flexible connections to equipment subject to settlement or frost heaves.


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## kolyan2k (Apr 13, 2014)

Well I have expansions on higher up run that emerge from ground and go up the vertical wall 4-5 feet or so. I did not install them in place where PVC emerge and goes right inside almost at ground level with LB. I am not even if there is room for them to be above the ground.

But I am pretty sure inspector wanted them in horizontal pcv underground. He signed it off anyway but said I need them for next time.


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## Kevin (Feb 14, 2017)

kolyan2k said:


> Well I have expansions on higher up run that emerge from ground and go up the vertical wall 4-5 feet or so. I did not install them in place where PVC emerge and goes right inside almost at ground level with LB. I am not even if there is room for them to be above the ground.


There's your problem. I've seen the ground settle and break an LB when there's no expansion joint. It's not just expansion and contraction of the pipe with PVC. As the ground settles under the conduit, so will the ground over the conduit, causing strain on the fittings without an expansion joint.

I did one job where a portion of the expansion joint was below grade due to where the LB had to go thru. Is it ideal to have half burried? No. Will it work? Probably.



Sent from my Samsung using Tapatalk


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## kolyan2k (Apr 13, 2014)

Thanks. I'll install them. Wires are not connected anywhere thankfully, just need to be careful cutting the pipe with wires inside


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## splatz (May 23, 2015)

The expansion fitting on the vertical riser portion is a good idea, to allow for settling, but I don't see where it's a code requirement. In most cases / most places a short length of PVC is not going to expand / contract the 1/4" where code requires the expansion fitting.


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## flyboy (Jun 13, 2011)

splatz said:


> The expansion fitting on the vertical riser portion is a good idea, to allow for settling, but I don't see where it's a code requirement. In most cases / most places a short length of PVC is not going to expand / contract the 1/4" where code requires the expansion fitting.


While it doesn't specifically mention expansion fittings, this is probably the code reference an inspector will reference. Here in the northeast they look for them.

300.5(J) Earth Movement. Where direct-buried conductors,
raceways, or cables are subject to movement by settlement
or frost, direct-buried conductors, raceways, or cables shall
be arranged so as to prevent damage to the enclosed conductors
or to equipment connected to the raceways.


Informational Note: This section recognizes “S” loops in
underground direct burial to raceway transitions, expansion
fittings in raceway risers to fixed equipment, and, generally,
the provision of flexible connections to equipment subject
to settlement or frost heaves.


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## emtnut (Mar 1, 2015)

I've overseen literally 1000's of miles of U/G plant ... Even with overboard gov't specs, never once saw an expansion joint underground :vs_laugh:


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## fmwowol (Aug 11, 2019)

Pipe is 2-3' u/g in a region with a 5' frost line.
It's going to move.
I'd think vertical expansion joint is sufficient, but my inspections tenure is limited to working in beach sand where we don't have freezing.
Let's see what the peers up north say their inspectors expect.


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## 99cents (Aug 20, 2012)

emtnut said:


> I've overseen literally 1000's of miles of U/G plant ... Even with overboard gov't specs, never once saw an expansion joint underground :vs_laugh:


Yep. Silly Americans scared of frozen dirt  .


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## joe-nwt (Mar 28, 2019)

I've had this discussion up here with our AHJs. CEC 12-1118 specifies exp joints needed where maximum expansion exceeds 45mm. There is a chart in Appendix B showing Coefficient of Linear Expansion, as well as an example calculation. The expansion for PVC is much higher than other types of conduit.

Got some info on average ground temperatures for our area (don't have them handy) and believe it or not, once you get to a certain length underground, to be code compliant expansion joints are required. Even if you think nothing would move in frozen ground, (it does) it certainly will move when the ground thaws.

We use them all the time coming out of the ground as the soil around here is fairly unstable. 

Without them I've seen anchored meter boxes get ripped off of block walls. The ground can be really heavy when it wants to.....

Just throwing this out there in case it may save you a headache down the line as expansion joints are easy to install when first running the conduit.


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## macmikeman (Jan 23, 2007)

99cents said:


> Yep. Silly Americans scared of frozen dirt  .



What is this frozen dirt you speak of?
https://youtu.be/WolhhbcOtYw?t=2


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## 99cents (Aug 20, 2012)

joe-nwt said:


> I've had this discussion up here with our AHJs. CEC 12-1118 specifies exp joints needed where maximum expansion exceeds 45mm. There is a chart in Appendix B showing Coefficient of Linear Expansion, as well as an example calculation. The expansion for PVC is much higher than other types of conduit.
> 
> Got some info on average ground temperatures for our area (don't have them handy) and believe it or not, once you get to a certain length underground, to be code compliant expansion joints are required. Even if you think nothing would move in frozen ground, (it does) it certainly will move when the ground thaws.
> 
> ...


Where it exits the ground makes sense. Underground, I’m not even sure if the piston would even operate properly.


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## joe-nwt (Mar 28, 2019)

I don't know either. They make us install them here anyway.

Interesting reading, last page:

https://www.nema.org/Standards/ComplimentaryDocuments/NEMA PRP 4-2009 (R2016) WATERMARKED.pdf

Says they aren't needed but to install lines below the frost line. Maybe because our frost goes much deeper here and because of permafrost they decided to make us put them in?


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## glen1971 (Oct 10, 2012)

joe-nwt said:


> I don't know either. They make us install them here anyway.
> 
> Interesting reading, last page:
> 
> ...


Last winter we had a lot of water lines in the area freeze, that have never frozen in the past 40+ years. Some of these are down 5-8'. How far down would one have to go to make sure you are below this year's and future year's frost lines? 

I agree that where the PVC emerges from the ground there should be one on each end, but I can't see how it would work, as 99 said. Even if it did, it may work for a couple of years, then there'd be enough grit inside it may not.


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## emtnut (Mar 1, 2015)

joe-nwt said:


> I've had this discussion up here with our AHJs. CEC 12-1118 specifies exp joints needed where maximum expansion exceeds 45mm. There is a chart in Appendix B showing Coefficient of Linear Expansion, as well as an example calculation. The expansion for PVC is much higher than other types of conduit.
> 
> Got some info on average ground temperatures for our area (don't have them handy) and believe it or not, once you get to a certain length underground, to be code compliant expansion joints are required. Even if you think nothing would move in frozen ground, (it does) it certainly will move when the ground thaws.
> 
> ...


I'd think you are in permafrost, so I wouldn't think there would be much temp change ???

In my area the frost line is 2-4' . The U/G plant was generally at about 3.5 feet.

Even so, the temperature change is minimal. 10˚C in the summer, to slightly below freezing in a bad winter.
We usually didn't go more than 75M between manholes.

We often added/replaced cable after 20yrs, and it slid right in.

I agree with @99cents ... the exp joint would fill with crap and seize up within a year or 2.


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## joe-nwt (Mar 28, 2019)

emtnut said:


> I'd think you are in permafrost, so I wouldn't think there would be much temp change ???


For the most part, we are not in permafrost. Ever try to dig in permafrost? Not the same as frozen soil you might run into. It is as hard as, or harder than concrete. I know, seems hard to believe.

Since I posted this morning, I sent an email with the NEMA literature to our AHJ asking the rationale behind forcing us to install expansion joints. No reply so far.


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## MechanicalDVR (Dec 29, 2007)

kolyan2k said:


> The job is already done but the inspector was kinda upset that I didn't use expansion fittings on my 200ft underground PVC run. The reason why I didn't use any is because pipe is like 2-3ft underground and temp changes are minimal there (I am not even sure if those expansions work underground) and manufacturer specs say that in general it's not needed underground as well. Inspector said there is earth movement and that's why they are needed, not because temp changes. But anyway, the main reason why I didn't install them because I used direct burial cable and PVC was only used for further protection. What do you think, expansions needed or not?
> 
> The other questions is this... When pipe emerges from ground and within like a foot or less goes straight inside the building with a 90, do you need expansion is this case?



You are misinterpreting what they are for. They are to compensate for frost unheavel and vertical thermal expansion and contraction.

There is uniform lateral temperature change, so no expansion device is needed in the buried horizontal run.


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## Incognito (Apr 14, 2019)

joe-nwt said:


> I don't know either. They make us install them here anyway.


They make you install them underground? 

It would have to be a pretty far run for code to require an expansion joint as the temperature does not change much underground.


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## MechanicalDVR (Dec 29, 2007)

Incognito said:


> They make you install them underground?
> 
> It would have to be a pretty far run for code to require an expansion joint as the temperature does not change much underground.


Exactly!

Somebody is a moron somewhere. 

How many millions of miles of plastic water and gas lines are run underground and never one expansion joint in any of them?


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## emtnut (Mar 1, 2015)

joe-nwt said:


> For the most part, we are not in permafrost. Ever try to dig in permafrost? Not the same as frozen soil you might run into. It is as hard as, or harder than concrete. I know, seems hard to believe.
> 
> Since I posted this morning, I sent an email with the NEMA literature to our AHJ asking the rationale behind forcing us to install expansion joints. No reply so far.


I've dug in frozen ground ... sometimes the backhoe almost gets airborne :biggrin:

I'm interested in what the AHJ gets back to you with !


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