Hi does anybody know off hand how much a 2" run of emt 100' long on a roof in New England expands. i know its listed in a formula in the code but thought this might be faster way of finding out.
thanks
Hi does anybody know off hand how much a 2" run of emt 100' long on a roof in New England expands. i know its listed in a formula in the code but thought this might be faster way of finding out.
thanks
The formula in the code is for PVC only. It will not work for EMT and you don't have to worry about it.
An article in the Oct/Nov issue of SOLARPRO magazine says a 200ft run of EMT with a temperature change of 110 degrees can expand 1.72 inches..."pipe guides along with expansion fittings allow for axial movement of the raceway"
Maybe the manufacturer of the product should be consulted for more information.
.000007 should be correct.My recollection is that steel expands/contracts about 7 millionths of an inch per inch per degree F. For comparison aluminum is 12 and PVC is 28. Now the hard part is getting the correct decimal for 7 millionths Ill take a stab at it: .000007
300.7(B) I.N. states 0.0000065 in. per inch of conduit for each ?F in temperature change..000007 should be correct.
Absolutely.... you have to consider what the expansion rate is of whatever it is attached to.
That's covered under 300.4(H) and requires the installation of an expansion/deflection fitting or other approved means in the run. Where such is required, it can also serve to satisfy 300.7(B).Although sometimes the surface it is attached to (like a metal roof) will have its own expansion joints.
Below is a diagram from the SolarPro Dec/Jan 2014 magazine issue...
40% steel to PVC is not too far behind :huh:Unless I am not understanding correctly, that seems to be indicating a 4 inch change of length in a 100 foot run, assuming this is rooftop applications it is not quite the same expansion rate of PVC but is not too far behind.
40% steel to PVC is not too far behind :huh:
I did not say that... :blink:If steel raceways are changing 4 inches in 100 feet, why are we not seeing either (A) similar requirements as with PVC or (B) seeing a lot of failure of the installations that are out there that are not using any expansion fittings? If it is changing that much in length and not being stressed by it, then it is likely that whatever it is attached to is changing dimensions at a similar rate.
I did not say that... :blink:
Steel raceways do not change 4" in 100'. Only ~1-5/8" for 100 degree swing at 40% of PVC. And then you can subtract the expansion of the structure to which it is attached (which you can also do for PVC, though Code does not mention this).
The diagram caption indicates straight rooftop on a parapet wall. Only the diagram was posted. There may have been associated parameters (e.g. temperature swing) mentioned in the document text... There was no mentioned temperature change in the figure I was replying to, but based on the source can kind of be assumed that it is rooftop type of conditions.
I agree... it is a bit much for EMT.I was mostly trying to point out a 4 inch change on a 100 foot run seemed a bit much and was maybe more likely to be something seen from PVC installations.