Eddy Current
Senior Member
I think its 352.44 that says something like a straight run with a 1/4 or greater has to have an expansion fitting. What does it mean by 1/4 or greater which way?
PVC expansion fitting 1/4 or greater?
- Thread starter Eddy Current
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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.
[Emphasis mine]
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.
[Emphasis mine]
As Jon noted, 1/3 inch of movement.
Determine the temperature variation to which the conduit will be subjected and see what the expansion characteristic is, for instance if the runs sees a 100 degree change then a 100 ft run would expand and contract 4.06", so a section roughly 6 ft long would move 1/4'.
Note the expansion fitting is needed between securely mounted items something like a vertical riser to a weatherhead would not need an expansion fitting.
The attached link explains it in more detail plus provides info on how to install and "set" the expansion joint:
http://www.carlon.com/Installation_Training/IT-NEMAEXJTA.pdf
Determine the temperature variation to which the conduit will be subjected and see what the expansion characteristic is, for instance if the runs sees a 100 degree change then a 100 ft run would expand and contract 4.06", so a section roughly 6 ft long would move 1/4'.
Note the expansion fitting is needed between securely mounted items something like a vertical riser to a weatherhead would not need an expansion fitting.
The attached link explains it in more detail plus provides info on how to install and "set" the expansion joint:
http://www.carlon.com/Installation_Training/IT-NEMAEXJTA.pdf
Last edited:
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Great link Gus! :thumbsup:
- Location
- Massachusetts
I am working on some repairs to a 150' long straight run of PVC that has worked the supports loose. Given a 100F change of temp (reasonable to expect here) it would be expected to change more than 5" in length over all.
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
Agreed. I have been putting them in the middle of runs and not securing the barrels.:blink: Thanks Gus.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Some people forget that they need to keep straps loose enough to allow the raceway to move, because it is going to move. Expansion fitting will not do what it is supposed to do if that is the case as tight straps are like having a box there that is fastened to mounting surface. If it can't move in a linear direction it will start bowing wherever it can.
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