Eddy Current
Senior Member
Anybody know a reference for this? Im guessing on long runs of pipe.
When to use expansion couplings?
- Thread starter Eddy Current
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Are you asking about expansion coupling for rigid steel or for PVC conduits ?
I believe steel expansion couplings are most often used in conjunction with building expansion joints or other structures like bridges, or as you mention, on fairly long runs..
PVC expansion joints are used considerably more often do the expansion of PVC conduit.
This link will provide with some idea of the expansion of steel conduit:
http://www.steelconduit.org/pdf/Co-Efficient%20Expansion.pdf
I believe steel expansion couplings are most often used in conjunction with building expansion joints or other structures like bridges, or as you mention, on fairly long runs..
PVC expansion joints are used considerably more often do the expansion of PVC conduit.
This link will provide with some idea of the expansion of steel conduit:
http://www.steelconduit.org/pdf/Co-Efficient%20Expansion.pdf
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brantmacga
Señor Member
- Location
- Georgia
- Occupation
- Former Child
352.44 for RNC
Eddy Current
Senior Member
If you don't overfill the pipe there shouldn't be any thermal expansion right, or are they talking about external environmental weather conditions? I cant think of any situation that would cause a pipe to move an 1/4 of an inch besides maybe an earthquake. I thought there was a code that stated how often to put a junction box, if so there shouldn't be any long runs of pipe requiring an expansion coupling.
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kwired
Electron manager
- Location
- NE Nebraska
PVC expands and contracts rather rapidly with temperature change.
Table 352.44 tells us how much change in length to expect for a given change of temperature.
Notice in the first row of the table that only a 5 degree change of temperature will make .20 inches of length change in 100 feet of raceway.
Now put the raceway in a place that is subject to 140 degrees from the coldest and hottest temperatures it is likely to encounter and it will change length 5.68 inches in 100 feet from one extreme to the other. That is .568 inches change in 10 feet - a little over double the .25 requirement maximum amount of change allowed without an expansion device. Even 5 feet of raceway at this temperature change will require an expansion fitting.
140 degree change is not that uncommon in central and northern states.
Table 352.44 tells us how much change in length to expect for a given change of temperature.
Notice in the first row of the table that only a 5 degree change of temperature will make .20 inches of length change in 100 feet of raceway.
Now put the raceway in a place that is subject to 140 degrees from the coldest and hottest temperatures it is likely to encounter and it will change length 5.68 inches in 100 feet from one extreme to the other. That is .568 inches change in 10 feet - a little over double the .25 requirement maximum amount of change allowed without an expansion device. Even 5 feet of raceway at this temperature change will require an expansion fitting.
140 degree change is not that uncommon in central and northern states.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
What does pipe fill have to do with expansion. It has to do with temp change.
BTW there is no code on distance a raceway is limited to.
Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
We've wired some long dairy barns, anywhere from 1100-2300' long steel buildings using EMT. The buildings have expansion joints every 2-300 feet or so. If you don't also install expansion joints/flex you will crush any boxes you may have in that run of conduit nearest their expansion joint. Don't ask me how I know this...:roll:
brantmacga
Señor Member
- Location
- Georgia
- Occupation
- Former Child
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
I was at a plant once where thermal expansion of a rigid run that was bolted to the side of a building had actually pulled a brick out of the wall a couple of inches. Pretty impressive.
The same plant had another spot where someone had run a piece of rigid that was run through the end of a building and cemented in place. The pipe expanded and pushed a chunk of concrete that was maybe a couple feet in diameter about an inch.
The same plant had another spot where someone had run a piece of rigid that was run through the end of a building and cemented in place. The pipe expanded and pushed a chunk of concrete that was maybe a couple feet in diameter about an inch.
Quarter mile is the longest I've ever went without a box. Per code, there is no call-out on the boxes...However a lot of job spec's will have call outs in them!
Doing it cheap, isn't necessarily right... but doing it right will be cheap in the long run...
Open Neutral
Senior Member
- Location
- Inside the Beltway
- Occupation
- Engineer
Steam lines used to use a jog/offset for this very reason; 3 ft over, 6 ft further, 3 back again....
kwired
Electron manager
- Location
- NE Nebraska
earlejohnson
Member
- Location
- ga.
Please elaborate on this.
earlejohnson
Member
- Location
- ga.
Open Neutral
Senior Member
- Location
- Inside the Beltway
- Occupation
- Engineer
Far better than any description of mine...
Eddy Current
Senior Member
What about strapping next to a rigid expansion coupling?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Don't forget about using an expansion coupling when exiting grade to allow for frost heaving and setttling of uncompacted fill. In my neck of the woods this is probably more important than using for thermal expansion. In this application you would strap the top of the expansion coupling and let everything below it float. A while back Mike sent out a newsletter with 10 of the most common code violations and non-use, or mis-use of expansion couplings was on it.
- Location
- Massachusetts
Don't skimp on clips that allow it to slide or it may sheer the mounting hardware .....
hmy:
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