Raceway Expansion from ∆T

[George Stolz]

Help me out here. Earlier last year, I had my nose stuck into 352.44 for the first time, and now there have been proposals accepted to introduce the concept of thermal expansion movement with expansion fittings in EMT as well.

How do we determine temperature change in the real world? In my area, winters drop to -30?F and summers peak out at 100?F in the shade, not considering the sun at all.

When dealing with sunlight on rooftops, we are told that we can just take a single temperature value out of a book and use it for all calculations all year long.

When considering an outdoor installation and raceway expansion, should we use those two extremes (-30?F / 100?F) to figure out how much our raceways will expand and contract?

If this change to EMT were to become code, how would we secure the EMT while still allowing the expansion fitting to relieve stress on the raceway? Usually, we would use mini's or strut straps every 10' to secure the EMT. If there are a dozen straps between the expansion fitting and the beginning and end of the raceway, what good would the expansion fitting do?

The coefficient of expansion for steel electrical metallic tubing is 1.170x10E-5 (0.0000117 mm per
mm of tubing for each degree C in temperature change)[0.650 X10E-5 (0.0000065 in. per inch of tubing for each degree
F in temperature change)]. The coefficient of expansion for aluminum electrical metallic tubing is 2.34x10E-5 (0.0000234
mm per mm of tubing for each degree C in temperature change)[1.30X10E-5 (0.000013 in. per inch of tubing for each
degree F in temperature change)].

Effectively, a 40?F temperature change on a 150' run of steel EMT would require an expansion fitting - right?

 

[kwired]

Help me out here. Earlier last year, I had my nose stuck into 352.44 for the first time, and now there have been proposals accepted to introduce the concept of thermal expansion movement with expansion fittings in EMT as well.

How do we determine temperature change in the real world? In my area, winters drop to -30?F and summers peak out at 100?F in the shade, not considering the sun at all.

When dealing with sunlight on rooftops, we are told that we can just take a single temperature value out of a book and use it for all calculations all year long.

When considering an outdoor installation and raceway expansion, should we use those two extremes (-30?F / 100?F) to figure out how much our raceways will expand and contract?

If this change to EMT were to become code, how would we secure the EMT while still allowing the expansion fitting to relieve stress on the raceway? Usually, we would use mini's or strut straps every 10' to secure the EMT. If there are a dozen straps between the expansion fitting and the beginning and end of the raceway, what good would the expansion fitting do?



Effectively, a 40?F temperature change on a 150' run of steel EMT would require an expansion fitting - right?

I think there is more to it than just the expansion of the raceway. With PVC you have a material that changes length with change of temperature much more rapidly than most anything you will mount it on.

If you have 150 feet of steel raceway mounted on a steel structure wouldn't they both expand at same rate and therefore no additional strain imposed on raceway? Just what I think - fire away if you disagree.

 

[iwire]

I think there is more to it than just the expansion of the raceway. With PVC you have a material that changes length with change of temperature much more rapidly than most anything you will mount it on.

If you have 150 feet of steel raceway mounted on a steel structure wouldn't they both expand at same rate and therefore no additional strain imposed on raceway? Just what I think - fire away if you disagree.

I agree with you.

How do we determine temperature change in the real world? In my area, winters drop to -30?F and summers peak out at 100?F in the shade, not considering the sun at all.

I use 100F here which can be exceeded. I should probably use a higher temp as all it takes is one real cold day to pull a coupling apart, or one real hot day to break the mounts off the building. (See link below)

If this change to EMT were to become code, how would we secure the EMT while still allowing the expansion fitting to relieve stress on the raceway?

I am sure we would see a entire new selection of high priced supports. I recently had to change some $3.00 uni-strut clips with around $15 ones.

Strut clips that allow PVC to move.

 

[kwired]

I agree with you.




I use 100F here which can be exceeded. I should probably use a higher temp as all it takes is one real cold day to pull a coupling apart, or one real hot day to break the mounts off the building. (See link below)





I am sure we would see a entire new selection of high priced supports. I recently had to change some $3.00 uni-strut clips with around $15 ones.

Strut clips that allow PVC to move.

cool, lets say it was 2 inch schedule 40 you have $30 of clamps for every $7 worth of raceway.

 

[George Stolz]

I am sure we would see a entire new selection of high priced supports. I recently had to change some $3.00 uni-strut clips with around $15 ones.

Which leads into the unasked question: Has anyone here ever seen EMT pull apart due to thermal expansion?

Strut clips that allow PVC to move.

Wow - I missed that thread - Nice work! The only thing I wonder about is how you got the expansion fittings installed without repulling the wire.

 

[chris kennedy]

How do we determine temperature change in the real world??

Here is a link to a table I use for roof top temps compliments of sellmorewire.org.