Pvc expansion joints

[steve66]

if the conduit turns vertical and extends out of the ditch to a "fixed" enclosure or fitting, an expansion joint is often used (sometimes required) to compensate for ground movement. Often times the conduit without an expansion joint will "settle" and pull loose from the enclosure.

Do you mean like this:

View attachment 3380

I just ran across that about an hour ago. Interesting coincidence. You can see from the color on the conduit that the conduit was once completely seated in the coupling (or at least it was mostly in the coupling).

I'm not sure I see any sign of glue, though.

Steve

 

[augie47]

no glue = TN expansion joint :smile: prevents damage to the meter base :smile:

 

[Pierre C Belarge]

Typically, from the ground to the bottom of a meterpan is approximately 4 feet. There will not be too much expansion of the PVC due to temperature changes.
Ground movement on the other hand can be significant due to extremes of temperature.
The picture is a good example of what we see here in the northeast. We do see 100F temperature swings during the course of the year. The ground movement comes via the frost heave. Some areas within the area I live show significantly different amounts of movement, based on the soil types.

 

[cpal]

The 4.06" (or the adjusted 2.03") of movement is for a run in ambient air temperature. An undergroiund run is not subject to the same ambient temperature or swings. For an area with a 100? ambient air temperature swing through all four seasons, an ambient soil temperature swing at 2' BFG may only be 50? (just a WAG).

Thanks

looking back at the posts I got a little off topic
My origional point would have been, a typical expansion fitting (of the slip type) is not listed for installations below grade. They do make a fitting for direct burrial that is the type I mentioned with the two coupelings conneceted with an inner tube ( or thats how they look)

 

[jimbo9927]

pvc expasion jionts

pvc expasion jionts

thanks guys for all your help i will look in to the codes mentioned and the carlon product. i will let you know how it works out

 

[troa303]

Do you mean like this:

View attachment 3380

I just ran across that about an hour ago. Interesting coincidence. You can see from the color on the conduit that the conduit was once completely seated in the coupling (or at least it was mostly in the coupling).

I'm not sure I see any sign of glue, though.

Steve

Seen that happen time and time again. That's why Pvc expansion joints are a good idea. Unfortunately, the're not cheap, hence why some electricians don't install them.

 

[kwired]

I wonder how plumbers deal with it?

most of their PVC pipe is not subject to temperature extremes, with the exception of vent pipes in an attic, most of them are not fixed on the ends so there is no place to go when the pipe expands. I have seen poorly supported horizontal runs in attics that start to sag when it gets hot up there this creates a trap and when freezing weather comes the pipe breaks and eventually leaks on the ceiling.

 

[kwired]

I understand an expansion fitting providing protection of a raceway during thermal expansion. But I have often questioned engineers that work for one of the local POCO's that wants expansion fitting on all service laterals what good does it do for ground settling or frost heave. Sure the fitting will expand or contract and protect the raceway but what happens to the conductors inside they will remain the same length or at the very least not change near as much as the PVC raceway. A 200 amp conductor being pulled by a settling trench will pull against the terminals in the meter socket and break the terminal because the conductor is too stiff to flex and no expansion fitting will protect the conductors within from this event.

 

[Smart $]

I wonder how plumbers deal with it?

most of their PVC pipe is not subject to temperature extremes, with the exception of vent pipes in an attic, most of them are not fixed on the ends so there is no place to go when the pipe expands. I have seen poorly supported horizontal runs in attics that start to sag when it gets hot up there this creates a trap and when freezing weather comes the pipe breaks and eventually leaks on the ceiling.

The ones that take expansion and contraction into consideration where needed put "saddles" (?) in the run...

 

[iwire]

The ones that take expansion and contraction into consideration where needed put "saddles" (?) in the run...

I see this all the time for gas lines run across the tops of buildings.


Back to electric work ........... no one is suggesting we have to use expansion joints under ground right??????

 

[ptonsparky]

I heard that suggestion once. Ignored it.

 

[Smart $]

........... no one is suggesting we have to use expansion joints under ground right??????

Seems to me that 352.44 is more than a suggestion

BTW, soil temp data can be obtained here: http://www.ncdc.noaa.gov/oa/soil/soiltemps/

 

[iwire]

Seems to me that 352.44 is more than a suggestion

How do you comply with any part of 352.30 especially the second par of the first sentence of 352.30 itself?

 

[don_resqcapt19]

From this Carlon document.

Use of Expansion Fittings Where
Concrete Encased or Direct Buried
In normal circumstances, expansion fittings are not needed with
concrete encased nonmetallic conduit since the movement of
the conduit will coincide with the expansion and contraction of
the concrete. The only place where an expansion fitting would
be utilized is where the concrete itself has an expansion joint.
In direct burial situations, expansion fittings are not needed
because the ground has relatively constant temperatures.
In cold areas, buried lines must be below the frost line to prevent
buckling during freezing and thawing cycles. In warmer areas,
the depth of cover protects against temperature extremes.

 

[M. D.]

But what about the settlement factor ,... expansion couplings are for thermal expansion of the conduit . the wires don't move much with thermal ,.. if the ground settles ,.the wire will need to move .. so... enter the slack box... is this what 300.5(J) is talking about .. not sure a regular expansion fitting is meant for earth settlement,.. though I did recommend it ...:roll:

 

[Twoskinsoneman]

But what about the settlement factor ,... expansion couplings are for thermal expansion of the conduit . the wires don't move much with thermal ,.. if the ground settles ,.the wire will need to move .. so... enter the slack box... is this what 300.5(J) is talking about .. not sure a regular expansion fitting is meant for earth settlement,.. though I did recommend it ...:roll:

Yes this is the real issue for underground PVC. Check out this settling. And this actually had an expansion joint. I don't think it was installed properly though not put in deep enough.

 

[Smart $]

How do you comply with any part of 352.30 especially the second par of the first sentence of 352.30 itself?

Not sure, as it is not very specific how or if it applies to direct burial.

I guess the best way to at least appear as an attempt to comply is to backfill so as to envelop the raceway(s) with something like "concrete sand" (essentially a mix of sand and pea gravel). See 300.5(F) and 300.50(D), second paragraphs of each.

PS: Don't kill the messenger :smile:

 

[Smart $]

From this Carlon document.

I agree with the part about concrete-encased PVC... but the latter part seems to contradict 352.44 and the fact that most soil temperatures at direct burial depth are not constant. Even soil temperatures at frost-line depth are not constant.

 

[M. D.]

I agree with the part about concrete-encased PVC... but the latter part seems to contradict 352.44 and the fact that most soil temperatures at direct burial depth are not constant. Even soil temperatures at frost-line depth are not constant.

Well if you have the circumstance to use them in the trench,.. they are listed for direct burial

 

[220/221]

The pics posted are not necessarily expansion/contraction related. More than likely this is an exmple of improper backfill. A LOT of times people (laborers) just chuck dirt back into the trench without properly supporting the pipe.