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#93156 05/05/05 08:12 PM
Joined: May 2005
Posts: 15
M
Member
running three hundred feet of 4inch pvc pipe horizontly on outside of building. table 352.44A talks about amount of expansion but iam confused about at what intervals do I need a expansion joint.


dukes
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#93157 05/05/05 08:19 PM
Joined: Jan 2003
Posts: 4,391
Moderator
The NEC does not tell us how many expansion joints would be needed.

It depends on the amount of temperature change and the amount of movement provided by the expansion joint.

In the last few days I have been using some expansion joints from Carlon that state right on them to use one every 30'


Bob Badger
Construction & Maintenance Electrician
Massachusetts
#93158 05/05/05 08:37 PM
Joined: May 2005
Posts: 15
M
Member
Thanks for the reply. It would be more cost effective to run steel?


dukes
#93159 05/06/05 12:14 AM
Joined: Jan 2004
Posts: 1,507
G
Member
Bob- How do you set your expansion joints with relation to the temperature and how does the inspector check this?


George Little
#93160 05/06/05 05:38 AM
Joined: Jan 2003
Posts: 4,391
Moderator
George the expansion joints that I have been using have instructions on each joint.

They do not say anything about how to set them dependent on temp, but I have wondered the same thing as you.

What they have is a scribe mark that shows how far to insert the PVC, that mark seems to be in the mid point.

I imagine if they are all set in the mid point and installed every 30' as instructed they will be enough overlap to deal with higher or lower temps than the day of installation.

These new joints are only about 6" long overall in 1.25" raceway and only cost a little more than a coupling.


Bob Badger
Construction & Maintenance Electrician
Massachusetts
#93161 05/06/05 07:01 AM
Joined: Oct 2000
Posts: 2,749
Member
Go to www.nema.org and download the following for free:

Expansion Joints for PVC Rigid Nonmetallic Conduit NEMA Standards Expansion Joints for PVC Rigid Nonmetallic Conduit

Status: Active
[No Document Number]

This guide provides information about when and how expansion joints are used. Discusses that fluctuations in temperature have a greater effect upon polyvinyl chloride (PVC) than more traditional construction materials, such as aluminum and steel.

Thermal expansion and contraction have significant effects on long, straight runs of conduit; therefore, expansion joints are used to accommodate changes in length. This prevents potentially harmful stresses in the conduit itself or in any supporting structures.

Electronic Copy
$0.00 [DOWNLOAD]


Joe Tedesco, NEC Consultant
#93162 05/06/05 08:23 AM
Joined: Jan 2004
Posts: 1,507
G
Member
Thanks Joe. Good information for all of us.


George Little
#93163 05/06/05 03:33 PM
Joined: Apr 2002
Posts: 7,389
Likes: 7
Member
Gentlemen:
In addition to Joe's info...Carlon has expansion joint info within their catalog. It also is available on there website.

Their tables, and a few easy calc's explain the 'setting' of the expansion joint.

John


John

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