Requirements for expansion in RMC in a vertical run?

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VinceS

Senior Member
When would a expansion joint be required for RMC in a vertical run? Article 344 doesn't seem to address this as table 352.44 does for PVC.

My application is RMC in the overhead of an industrial steel trussed roof. The building isn't air-conditioned. The vertical drops to various equipment and wire-ways located 35 feet below are where my concerns lie.

I may be overly concerned but desire any rules of thumb, voices of experience or calibration, (ie... "Its in the code you missed it.")

Thank in advance...
 
The use of expansion fittings for RMC in runs the length you mention is rare.

Take a look at the FPN located just after 300.7(B).
It does give some guidance as to the length of RMC in regards to the expansion coefficient.

I can tell you after you read it that the multiplier will be:

0.078"/1000ft for each degree of F in temperature change.

It take alot of temperature change and distance of RMC for expansion issues to arise.
 

Smart $

Esteemed Member
Location
Ohio
The use of expansion fittings for RMC in runs the length you mention is rare.

Take a look at the FPN located just after 300.7(B).
It does give some guidance as to the length of RMC in regards to the expansion coefficient.

I can tell you after you read it that the multiplier will be:

0.078"/1000ft for each degree of F in temperature change.

It take alot of temperature change and distance of RMC for expansion issues to arise.

Especially if it is supported by or secured to structural steel, as it too expands and contracts.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Especially if it is supported by or secured to structural steel, as it too expands and contracts.
And while the code does not support this idea, I see no purpose in using expansion devices when the steel conduit is run parallel with and on a steel structure that will have the same expansion coefficient.
 

iwire

Moderator
Staff member
Location
Massachusetts
The only time I have used expansion joints in steel conduits is on horizontal runs when we pass an expansion joint in the building. :smile:
 
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