PVC and expansion

[electrofelon]

So I was looking through the pvc conduit expansion tables and I was surprised to find out that in an outdoor application, pretty much any length ten feet or over needs an expansion coupling?? This doesn't seem right, or at least I never see it in practice. How many of you guys strictly adhere to this? Come on be honest! My assumption is 65 degree temp differential which seems reasonable pretty much anywhere, except Hawaii.

 

[JohnE]

If it is between 2 fixed points, we enforce generally enforce it. For example, and overhead service does not have the conduit run between 2 fixed points. Entire conduit run including weatherhead can expand. Although I have heard of some inspectors requiring an expansion coupling for this application, which is wrong IMO.

 

[al hildenbrand]

Is that 65?C or 65?F?

 

[pierre]

In the lower NY area we have approximately a 90F differential. Expansion fittings are being installed and inspected.

 

[bphgravity]

Don't forget to add 30? F for raceways exposed to direct sunlight.... :wink:

 

[electrofelon]

Al,

I was using F, and I think that is what the NEC tables are calculated with.

Bryan,
Is the extra 30 degrees mentioned in the NEC, or just logical asuumption?

 

[benaround]

Electofelon,


Remember to support it about every 3' or it will sag in no time!

 

[pierre]

Bryan
Are you preparing us for the future?

 

[al hildenbrand]

Electrofelon,

The reason I asked after the temperature scale was because 65C? turn into 117F? which is what I could kind of feel comfortable with. Here, we average minus 20?F to 100?F, or, a 120F? differential.

The 2005 NEC Handbook commentary has this to say:

Expansion fittings are generally provided in exposed runs of rigid nonmetallic conduit where (1) the run is long, (2) the run is subject to large temperature variations during or after installation, or (3) expansion and contraction measures are provided for the building or other structures. Rigid nonmetallic conduit exhibits a considerably greater change in length per degree change in temperature than do metal raceway systems.
In some parts of the United States and other countries, outdoor temperature variations of over 100?F are common. According to Table 352.44(A), a 100-ft run of PVC rigid nonmetallic conduit will change 4.06 in. in length if the temperature change is 100?F.
The normal expansion range of most larger sizes of rigid nonmetallic conduit expansion couplings is generally 6 in. Information concerning installation and application of this type of coupling may be obtained from manufacturers' instructions.
Expansion fittings are seldom used underground, where temperatures are relatively constant. If rigid nonmetallic conduit is buried or covered immediately, expansion and contraction are not considered a problem.

 

[bphgravity]

I believe the 30? F is a listing instruction by all the manufacturer's. Carlon specifies it in their instructions. :?:

 

[raider1]

The 30 degrees F is also mentioned in FPN No. 2 to 310.10.

Conductors installed in conduits exposed to direct sunlight in close proximity to rooftops have been shown, under certain conditions, to experience a temperature rise of 30 degrees F above ambient temperature on which the ampacity is based

Chris

 

[pierre]

I have mentioned before, that I believe this FPN is going to lead to a future code requirement, as a result of studies being performed now.