Expansion fittings - again

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peter d

peter d

Senior Member
Location
New England
Would you use expansion fittings if the soil was heavily compacted and nearly has hard as rock (almost impossible to hand dig)? Only about 18" is emerging from grade and then into the building with an LB. These are raceways for outbuildings. Climate is the highly variable northeast (extreme heat to extreme cold is the norm.)
 
peter d said:
Would you use expansion fittings if the soil was heavily compacted and nearly has hard as rock (almost impossible to hand dig)? Only about 18" is emerging from grade and then into the building with an LB. These are raceways for outbuildings. Climate is the highly variable northeast (extreme heat to extreme cold is the norm.)
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In general we use expansion fittings wherever a complete raceway emerges from ground. A sleeve that protects direct bury conductors, No, but that is here and me.

I did omit one where the conduit was laying on the footings. :ashamed:
 
There is a pvc expansion table for calculating expansion in the NEC. The NEC requires expansion fittings if the conduit is expected to move more than a 1/4". It's easy enough to run the numbers and see how much movement you should expect.

Over here, I know based on what you described, I would not be using an expansion fitting. But, we also don't get the frost heave other areas do as well. So you have temperature and frost heave both playing a part in whether or not you would need expansion fittings.
 
You have to decide if 300.5(J) applies.

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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Even with no settlement, such an installation is still subject to frost heave.

Just look at paved roads in your area. The earth is very compacted and the surface is hard as a rock. Yet they still get all wavy, cracked and soon have potholes, all a result of frost heave. So what do you think?
 
Smart $ said:
Even with no settlement, such an installation is still subject to frost heave.

Just look at paved roads in your area. The earth is very compacted and the surface is hard as a rock. Yet they still get all wavy, cracked and soon have potholes, all a result of frost heave. So what do you think?
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Yes, frost heave is certainly and issue and that's why I'm going to install them. They cost me all of $70 for several runs of pipe and that's very cheap insurance if one raceway were to move even 1/2" because it would do some damage. But, I also realize they are not commonly used in other parts of the country so I was curious how people make a judgement on whether they use them or not.
 
Does anyone kwon why these things are so expensive. A 1/2" PVC expansion fitting costs about $13. :rant:
 
infinity said:
Does anyone kwon why these things are so expensive. A 1/2" PVC expansion fitting costs about $13. :rant:
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This will blow your mind - I pay around $15.xx for a 1.25", 1.5" and 2". :blink: Basically the same price for those three sizes and I pay around the same price you mentioned for a 1/2" one as well. There is no consistency with their pricing at all.
 
ActionDave said:
I use them all the time for under ground PVC. I like the inch or so of slop that they allow when landing in a panel or gluing up to an LB.
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I agree. I think it is good practice, particularly here in the northeast with freezing. For the 2 inch size, you can make your own with 2.5 pvc and this sometimes give you the added benefit of not having a concentric knockout
 
electrofelon said:
... For the 2 inch size, you can make your own with 2.5 pvc and this sometimes give you the added benefit of not having a concentric knockout
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I thought about mentioning BYOXF...but we're on a Code forum. :D

352.6 Listing Requirements. PVC conduit, factory elbows,
and associated fittings shall be listed.
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Anyway, there are a few different sizes that match up... some are better with a SCH80-SCH40 pairing.... and they do make reducers.
 
electrofelon said:
I don't really see a "home made" slip riser as being a listing violation. It's still listed conduit and listed fittings....
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I see it as the Arlington fitting when used per instructions is listed for the purpose, but a standard 2.5 inch TA and short length of 2.5 inch PVC is not listed for the purpose though it is essentially about the same thing. I will admit to using the latter in a pinch and it worked just fine. Was not on a job that was going to be inspected though - so not sure how it would have went if an inspector saw it.
 
kwired said:
I see it as the Arlington fitting when used per instructions is listed for the purpose, but a standard 2.5 inch TA and short length of 2.5 inch PVC is not listed for the purpose though it is essentially about the same thing. I will admit to using the latter in a pinch and it worked just fine. Was not on a job that was going to be inspected though - so not sure how it would have went if an inspector saw it.
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The advantage of the Arlington is that it fits into a 2" KO even though the "slip" portion of PVC is 2.5".
 
infinity said:
The advantage of the Arlington is that it fits into a 2" KO even though the "slip" portion of PVC is 2.5".
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Around here you can get a 1 piece "slip riser" that is a piece of 2.5 sched 40 PVC (says right on it) and the end is shrunk down into a 2" TA. As I mentioned, I often prefer the 2.5 TA cuz it gets rid of the concentric . IIRC the slip riser version is a bit cheaper than a regular expansion coupling, but still ridiculous for what it is, maybe $20. Ive never had an inspector say anything about my home made version, but inspections are a joke around here.
 
To me this is again a gamble I will not take.

The cost to include it from the beginning pales in comparison to the cost, hassle and loss of confidence of the customer if the inspection fails.
 
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