When to use expansion couplings?

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tkb said:
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You will see this same things when gas lines are run across a roof.
 
electrofelon said:
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.
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This has always been a pet peeve of mine, people wanting an expansion fitting for settling of uncompacted fill.

The expansion fitting protects the raceway from damage from movement but what protects the conductors that are inside of it? Extra slack inside boxes or cabinets may be fine for smaller conductors but for larger conductors that just does not work most of the time, if it is going to move it will strain terminals on things like breakers or especially meter sockets. Do the job right and make sure the fill is compacted correctly has always been my approach.
 
Anybody know a code reference for Rigid expansion couplings? Im looking for a code reference on couplings that are made to move back and forth not expand and not PVC.
 
What could cause pipe to move 1/4"?

Apart from an earthquake, there are many things that can cause this to happen.

As one poster suggested, changes in the ambient temperature and a long pipe run can cause all those tiny expansions to add up to 1/4". Every material expands at a certain rate, and the amount accumulates.

Your mounting method can affect just how this expansion affects the installation. Something rigidly attached - like the ladder going up a water tower- will expand by actually bowing between supports. This is one reason so many outdoor PVC pipe runs look like soggy spaghetti- the plastic deforms when it gets heated by the sun.

Another cause of pipe moving is when the structure itself moves. For example, frost heave in the soil can actually break the PVC of an underground service feed - one reason folks in northern climes want to bury the stuff well below the frost line. Other causes of movement are vibration, as well as changes to the loading of the structure. That's why you'll often see expansion fittings used at the seams in parking garages and bridge mounts.

This change in dimension causes the most trouble where the pipe changes direction. OK, so the radius of a bend and the degree of a bend can flex, so as to absorb much of this movement- but what happens at a 'hard' turn, like with an LB? Something has to give. That's what the expansion fitting is for.
 
renosteinke said:
What could cause pipe to move 1/4"?

Apart from an earthquake, there are many things that can cause this to happen.

As one poster suggested, changes in the ambient temperature and a long pipe run can cause all those tiny expansions to add up to 1/4". Every material expands at a certain rate, and the amount accumulates.

Your mounting method can affect just how this expansion affects the installation. Something rigidly attached - like the ladder going up a water tower- will expand by actually bowing between supports. This is one reason so many outdoor PVC pipe runs look like soggy spaghetti- the plastic deforms when it gets heated by the sun.

Another cause of pipe moving is when the structure itself moves. For example, frost heave in the soil can actually break the PVC of an underground service feed - one reason folks in northern climes want to bury the stuff well below the frost line. Other causes of movement are vibration, as well as changes to the loading of the structure. That's why you'll often see expansion fittings used at the seams in parking garages and bridge mounts.

This change in dimension causes the most trouble where the pipe changes direction. OK, so the radius of a bend and the degree of a bend can flex, so as to absorb much of this movement- but what happens at a 'hard' turn, like with an LB? Something has to give. That's what the expansion fitting is for.
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If the ladder going up the water tower is made of same material as the tower will they not expand or contract at same rate?

If the LB is not rigidly fastened to anything why wouldn't it flex. Isn't the bigger issue a straight run that is rigidly fastened at each end, there is no place to expand so the middle ends up bowing.
 
Dennis Alwon said:
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.
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My guess: he is thinking of heat generated by current flow. Of course the derating for multiple circuits serves to keep the heat gain about the same.

Another note: aluminum conduit thermal expansion is greater than steel,but less than PVC.

On long, vertical risers the thermal expansion coefficient difference between the steel conduit and vertical support requirements create another set of problems to be solved.
 
iwire said:
Don't skimp on clips that allow it to slide or it may sheer the mounting hardware ..... :eek:hmy:

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For installations like this, long horizontal runs of conduit, I always install a saddle washer and square or spring nut against the bottom strap in the strut. If the conduit does move downward it will not fall off of the strut as shown in Bob's photo's.
 
infinity said:
For installations like this, long horizontal runs of conduit, I always install a saddle washer and square or spring nut against the bottom strap in the strut. If the conduit does move downward it will not fall off of the strut as shown in Bob's photo's.
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The pipes did not fall off the strut, the strut fell off the wall. :D

The new struts are in place waiting for the pipes to be raised back up.


Strut clips that allow PVC to move.
 
Kwired, in my examples I was trying to draw your attention to the role geometry plays in expansion issues.

Even when the materials are the same -and with a water tower, there are plenty of wood or masonry support frames holding up metal or plastic tanks out there- the shape of the pieces will influence the way things move. Probably the best example of this is found with old-fashioned sleeve bearings; when heated, the tubular pieces actually show a reduction of the ID, as the metal expands into the bore.

Likewise, I used the LB to illustrate the idea that where you have a 90-degree change in direction, you have a 'fixed' point against which the forces will act. With a bend, there is all that transition length over which the movement can be spread; with a sharp right turn you don't have that buffer. There's no curved section of pipe to act as a spring.
 
renosteinke said:
Kwired, in my examples I was trying to draw your attention to the role geometry plays in expansion issues.

Even when the materials are the same -and with a water tower, there are plenty of wood or masonry support frames holding up metal or plastic tanks out there- the shape of the pieces will influence the way things move. Probably the best example of this is found with old-fashioned sleeve bearings; when heated, the tubular pieces actually show a reduction of the ID, as the metal expands into the bore.

Likewise, I used the LB to illustrate the idea that where you have a 90-degree change in direction, you have a 'fixed' point against which the forces will act. With a bend, there is all that transition length over which the movement can be spread; with a sharp right turn you don't have that buffer. There's no curved section of pipe to act as a spring.
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I don't disagree, I will say with the case of the LB, the smaller the raceway the more easily it will move. With metal raceway we usually are not talking about much movement as compared to PVC raceways. Locations of supports will also make a difference of what can move.
 
I am talking about rigid expansion couplings run in the air not pvc on a wall. Does anybody have a code reference for rigid expansion couplings?
 
Eddy Current said:
I am talking about rigid expansion couplings run in the air not pvc on a wall. Does anybody have a code reference for rigid expansion couplings?
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There is no NEC requirement to use a fitting for expansion and contraction of rigid metal conduit.

Often it is a job specification when you cross a building expansion joint.
 
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