Expansion fittings

[cosmos]

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.

 

[S'mise]

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.

 

[justdavemamm]

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".

 

[infinity]

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"?

 

[wbalsam1]

Far as I know it is not addressed by the NEC......

See 300.7(B) and the FPN

 

[mdshunk]

You'd be well advised to use an expansion fitting or a flexible section across building expansion joints and seismic joints.

Photo courtesy of the International Association of Electrical Inspectors (IAEI)

 

[hardworkingstiff]

You'd be well advised to use an expansion fitting or a flexible section across building expansion joints and seismic joints.

Photo courtesy of the International Association of Electrical Inspectors (IAEI)

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?

 

[augie47]

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.

 

[hardworkingstiff]

augie

augie

Do you remember that thread? Was there ever a consensus as to whether you can use a rigid coupling for this conversion?

 

[augie47]

thread

thread

http://forums.mikeholt.com/showthread.php?t=85913&highlight=coupling

 

[vhay]

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?

 

[cosmos]

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.)