Deflection couplings

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pgordon

pgordon

Senior Member
Location
Maine
Occupation
Electrician
I have a 250' run of 3" emt conduit outside on a wall of a building . The conduit runs over (10) 3/4" structure joint.
I am having a hard time finding a listed deflection coupling listed for EMT. They are listed for PVC or RMC but none for EMT .
Plus they are $350 + each
Can i use short pieces of liquid tight for this application ?
A 3/4" structural joint should only need a foot of liquid tight i would think.
 
Listed schmisted.

http://www.homedepot.com/p/Fernco-3...ic-Socket-Flexible-Coupling-1060-33/203310961

*grin*

(Tongue firmly in cheek)

Seriously, this has been discussed several times, google is your friend:
http://forums.mikeholt.com/showthread.php?t=175409
http://forums.mikeholt.com/showthread.php?t=140164

Which pointed to this resource:
http://www.cooperindustries.com/con...s_conduitexpansionjointsforemt.resources.html

Only $600 each (gaak)
http://www.newark.com/crouse-hinds/xjg84-emt/conduit-expansion-joint-steel/dp/38X5685

It appears that most of the difficulty and expense with these fittings is to create something that provides proper ground bonding and also is internally smooth to permit cable pull, even as everything moves.

-Jon
 
winnie said:
Listed schmisted.

http://www.homedepot.com/p/Fernco-3...ic-Socket-Flexible-Coupling-1060-33/203310961

*grin*

(Tongue firmly in cheek)

Seriously, this has been discussed several times, google is your friend:
http://forums.mikeholt.com/showthread.php?t=175409
http://forums.mikeholt.com/showthread.php?t=140164

Which pointed to this resource:
http://www.cooperindustries.com/con...s_conduitexpansionjointsforemt.resources.html

Only $600 each (gaak)
http://www.newark.com/crouse-hinds/xjg84-emt/conduit-expansion-joint-steel/dp/38X5685

It appears that most of the difficulty and expense with these fittings is to create something that provides proper ground bonding and also is internally smooth to permit cable pull, even as everything moves.

-Jon
Click to expand...

A slightly less sucky price:

http://www.galco.com/buy/Crouse-Hinds/XJG84-EMT



SceneryDriver
 
Jim1959 said:
Seems like you could run the conduit on Unistrut and avoid the issue.
Click to expand...
If the strut is securely fastened to both sides of the building expansion joint and the conduit is securely clamped to the strut, what happens when there is movement between each side of the expansion joint?
 
pgordon said:
I have a 250' run of 3" emt conduit outside on a wall of a building . The conduit runs over (10) 3/4" structure joint.
I am having a hard time finding a listed deflection coupling listed for EMT. They are listed for PVC or RMC but none for EMT .
Plus they are $350 + each
Can i use short pieces of liquid tight for this application ?
A 3/4" structural joint should only need a foot of liquid tight i would think.
Click to expand...

You're going to spend more than $350 in LFMC 3" connectors, LFMC, rigid couplings, and raintight connectors just to make a LFMC transition. That's not counting all the labor to put it together either.

I'm curious if you couldn't just use those B-Line strut straps made to allow for a slip fit?
 
Cow said:
...
I'm curious if you couldn't just use those B-Line strut straps made to allow for a slip fit?
Click to expand...
The physics says you can with just one expansion joint if that is all that is needed... but Code implies you have to use a listed fitting for each joint [300.4(H)].

Best to contact AHJ to get preapproval (in writing).
 
Last edited:
pgordon said:
I have a 250' run of 3" emt conduit outside on a wall of a building . The conduit runs over (10) 3/4" structure joint.
I am having a hard time finding a listed deflection coupling listed for EMT. They are listed for PVC or RMC but none for EMT .
Plus they are $350 + each
Can i use short pieces of liquid tight for this application ?
A 3/4" structural joint should only need a foot of liquid tight i would think.
Click to expand...

Is this for a tilt slab construction?. If so you do not need to install expansion fittings. The structural joint in this application is just how they attach the slab to the steel.
If you do need to use an expansion fitting that is all you would need. An expansion / deflection fitting allows for expansion and contraction along with sideways movement. That is why it is called deflection.
As for liquid tight this is not approved for expansion. Although it is good for deflection.
You could use a strut clamp like this https://www.gexpro.com/usg/Root-Cat...-B-Line-B2417-3ZN-STRUT-MOUNTED-PIPE/p/169553. You would still need to fix both ends of the conduit run and install at least 1 expansion fitting.
 
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