Need opinion on pvc expansion fittings

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peterrudart

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I have a run of 1" pvc that is 10' vertical, 40' horizontal, then 6' vertical all between an LB and a disco. This is in Minnesota so i assume a 100 degree temp change. How many expansion fittings should i use and where best to use them?
 
Relative to the horizontal run, do both vertical runs go up or both go down? Or does one go up and one go down?

Cheers, Wayne
 
2017 NEC 352.44 Expansion Fittings. Expansion fittings for PVC conduit shall be provided to compensate for thermal expansion and contraction where the length change, in accordance with Table 352.44, is expected to be 6 mm (1∕4 in.) or greater in a straight run between securely mounted items such as boxes, cabinets, elbows, or other conduit terminations

Per the table, at 100F temperature delta, the length change is 4" per 100 ft. So the 6 ft section will only move 0.24" and 352.44 doesn't require anything. Still would probably be wise not to strap the horizontal run right next to that elbow; if you strap it 3' - 8' away (depending on the conduit size), then the elbow could move up/down slightly.

The 10 ft run will move 0.4", so if the elbow where it turns horizontally is restrained vertically, it will require an expansion fitting. Not sure what the limit is to allowing that elbow to move by again keeping the closest strap on the horizontal run as far away as possible; maybe that would accommodate 0.4" of movement, maybe not.

The 40 ft run will move 1.6", so an expansion fitting is required.

Cheers, Wayne
 
marmathsen said:
I'm curious why you ask this...
Click to expand...
Just trying to get a picture of what the conduit will want to do when it expands. With the "up/over/down" geometry, the horizontal run will want to move up and down, and rotate slightly because the up and down lengths are different. With an "up/over/up" geometry, the horizontal run would mostly just want to rotate about a fixed point, which would be the midpoint if the two up runs are the same length.

Is there perchance a way to strap horizontal PVC such that in addition to the PVC moving axially through the strap as is typical, the whole strap can move up and down? E.g. a piece of strut with some sort of spring loaded clamp that could slide in the strut when enough force is applied, but will hold the weight of the PVC statically otherwise? If so, then using those on the horizontal run would eliminate the need for any expansion fittings on the vertical portions.

Cheers, Wayne
 
wwhitney said:
Just trying to get a picture of what the conduit will want to do when it expands. With the "up/over/down" geometry, the horizontal run will want to move up and down, and rotate slightly because the up and down lengths are different. With an "up/over/up" geometry, the horizontal run would mostly just want to rotate about a fixed point, which would be the midpoint if the two up runs are the same length.

Is there perchance a way to strap horizontal PVC such that in addition to the PVC moving axially through the strap as is typical, the whole strap can move up and down? E.g. a piece of strut with some sort of spring loaded clamp that could slide in the strut when enough force is applied, but will hold the weight of the PVC statically otherwise? If so, then using those on the horizontal run would eliminate the need for any expansion fittings on the vertical portions.

Cheers, Wayne
Click to expand...
Interesting puzzle to consider. I'm picturing a mini hanger mounted into some sort of slide change so it allows movement in one direction but not the other. I'll get right to work in developing that

Rob G, Seattle
 
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