I can't find anywhere in the NEC that specifically prohibits using ty raps to fasten PVC to building frame members. I have a contractor fighting me on this issue. We have a newly constructed greenhouse at our new high school; the interior is classified as a wet location. I made them remove tie wire in a couple of areas where they had to run conduit parallel to existing strut. Since unistrut straps will only work on a perpendicular install, they went back with ty raps. I'm trying to get the engineering firms to get them to add strut where neccesary, but in the meantime I'm trying to find out if ty raps are prohibited for use as a means of "fastening". ??
Using a menralac one hole pipe clamp with a uni-strut nut will allow securing to the uni-strut in any direction, and I agree the NEC allows wire ties to secure conduit, but the problem with PVC is expansion, like vinyl siding it must be allowed to move, this means the straps or clamps used must allow the pipe to slide through them, and expansion joints must be used when runs are over a certain length, or you wind up with a spaghetti mess. 352.30
When a job call for exposed PVC I tend to install more supports than the code requires, to keep it running straight table 352.30 allows 1/2"-1" to be supported every 3' on 1/2" I do 2' supports, I even go over board with expansion joints, when the conduit is between fixed points, or 90? turns, but here we can have over 90? temp in the summer and go down to -10? in the winter.
Inside runs are not as much a problem in a controlled environment, but it does seem to shrink over time when exposed to high temps, which can pull out of boxes and fittings.
hmy:
