2" emt expansion rough estimate
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kwired
Electron manager
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- NE Nebraska
Probably not enough to be concerned about it.
If the roof is steel, consider the fact that it will expand nearly the same amount.
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- Massachusetts
The formula in the code is for PVC only. It will not work for EMT and you don't have to worry about it.
kwired
Electron manager
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- NE Nebraska
Steel will expand and contract with temperature changes, just not anywhere near the amount that PVC will. I don't know the change for 100 deg @ 100 feet long but would guess it is only like a tenth of an inch at the most, which is not even close to the 4 inches you may see from a PVC object. Like I said before - if this is on a steel roof, the object it is attached to will expand at very similar rate and nothing will be impacted by any difference in change between the two.
Here is the application white rubber membrane roof 2"EMT about 120' total run set on Caddy rubber blocks. fixed on both ends. was unsure if expansion fittings were needed in this application. In other places on this roof they are running conduits over building expansion joints with no expansion fittings and i know that that is a code violation. the first picture is of the long run and the 2nd shows 2 2" EMT conduits going over a building expansion joint.
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- Massachusetts
If there is a building expansion joint you cross you would need an expansion fitting on the EMT as you said.
But you will not need one where there is none it crosses.
But you will not need one where there is none it crosses.
300.7(B) Informational Note says steel can be figured at 0.20 times the values in Table 352.44... so approx. 1 inch for 120' with a 100?F differential.
That said, the roof may have a rubber memebrane, but the "pan" is likely steel supported with steel trussing. With the rubber membrane being white, the steel below will experience less differential, especially while occupied and HVAC operating. However, the roof will expand and contract some. WAG perhaps 50% that of the conduit, so you're still looking at about 0.5" difference.
That said, the roof may have a rubber memebrane, but the "pan" is likely steel supported with steel trussing. With the rubber membrane being white, the steel below will experience less differential, especially while occupied and HVAC operating. However, the roof will expand and contract some. WAG perhaps 50% that of the conduit, so you're still looking at about 0.5" difference.
shortcircuit2
Senior Member
- Location
- South of Bawstin
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.
Maybe the manufacturer of the product should be consulted for more information.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
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
Ill take a stab at it: .000007
kwired
Electron manager
- Location
- NE Nebraska
.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
Using the 200 foot run @ 110 deg change that would amount to 2400 inches x 110 degrees x .000007 = 1.848 inches of change.
Seems like a lot of change and you would think we would see more expansion fittings than we do on steel raceways, but at same time you have to consider what the expansion rate is of whatever it is attached to. If it is attached to a steel surface it will change at about the same rate.
300.7(B) I.N. states 0.0000065 in. per inch of conduit for each ?F in temperature change.
Absolutely.
...or should that be relatively?
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- Placerville, CA, USA
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- Retired PV System Designer
Although sometimes the surface it is attached to (like a metal roof) will have its own expansion joints.
In which case you have to look at the structure under it. Which may not heat up at all.
Tapatalk...
In which case you have to look at the structure under it. Which may not heat up at all.
Tapatalk...
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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.
shortcircuit2
Senior Member
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- South of Bawstin
kwired
Electron manager
- Location
- NE Nebraska
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:
kwired
Electron manager
- Location
- NE Nebraska
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).
kwired
Electron manager
- Location
- NE Nebraska
OK, maybe I made a bad comparison or could have at least worded it much better. 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 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.
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
I agree... it is a bit much for EMT.
And for those that don't know, the expansion fitting can be placed anywhere between straps. It does not have to be placed adjacent to a strap as shown in the diagram. Additionally, intermediate straps are not required either, such as those shown in the 200' and 400' runs.
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