Expansion fittings

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cosmos

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Considering that all conduits will expand and contract with temperature change; how much of an expansion (eg. 1/8") is generally permitted without requiring an expansion fitting? I noticed a 100' run of rigid steel conduit with threaded fittings being installed outdoors between boxes without one; and I estimate 1" of possible consequential movement.
 
Far as I know it is not addressed by the NEC. Aside from the 1/4" PVC rule, Metal can expand and contract without breaking (with in reason). I see them used between building using RMC but thats about it. Just my 2 cents.
 
One inch of steel will expand 0.00000645 inches for every degree increase in temperature. This would be about 16 inches per mile for a 40 degree change. A 100' run is about 0.3096".
 
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Dave did the math. There is no reason to consider the thermal expansion of 100' of RMC. Where did you come up with the 1"?
 
You'd be well advised to use an expansion fitting or a flexible section across building expansion joints and seismic joints.

buildingexpansionjoint.jpg

Photo courtesy of the International Association of Electrical Inspectors (IAEI)
 
mdshunk said:
You'd be well advised to use an expansion fitting or a flexible section across building expansion joints and seismic joints.

buildingexpansionjoint.jpg

Photo courtesy of the International Association of Electrical Inspectors (IAEI)
Click to expand...

I remember a question a while back about whether it was permissible to use a rigid coupling to convert from rigid to flex. Since this photo is courtesy of the IAEI, does that mean that it is OK to use a rigid coupling to covert from rigid to flex?
 
Iaei

Iaei

Thank you, Lou

I don't know how many times in my life a picture of an electrical installation
demonstarting one point, introduces a host of other questions/points.
That electrician proudly standing by his work on the cover of EC&M turns out to be totally embarassed when the commernts start. :)
 
This seems like much ado about nothing. What are the other options? A flex connector with female threads perhaps? Can someone give an example of a case where a rigid conduit coupling would not be acceptable to use on rigid conduit?
 
Thanks

Thanks

Thanks for all the replies! Dave/Trevor, my 1-inch RSC expansion derived from NEC Hanbook FPN for Article 300.7(b). (Expansion table for PVC 352.44(a) times 20% for RSC.)
 
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