expansion coupling requirement

[gserve]

What is the minimum horizontal length of PVC conduit that can be run before an expansion couping is required by code? Code reference please. Thanks

 

[iwire]

That depends on the expected temperature range.

352.44 Expansion Fittings.
Expansion fittings for RNC shall be provided to compensate for thermal expansion and contraction where the length change, in accordance with Table 352.44(A) or (B), is expected to be 6 mm (1/4 in.) or greater in a straight run between securely mounted items such as boxes, cabinets, elbows, or other conduit terminations.

 

[mdshunk]

Non min or max for 300.7(B) installations. You just need something.

Normally it's controlled by 352.44 and table 352.44(A).

 

[mdshunk]

I guess I was having a typing race with Bob, and didn't realize it.

Here's a very nice NEMA document on expansion joints that is probably the best aid for applying the code to PVC expansion joints. http://www.nema.org/stds/expansionjoints-pvc.cfm#download

 

[infinity]

As Bob said you need to know the temperature range in which the conduit is installed. For here in NJ the yearly change is about 100 degrees. Knowing that and using table 352.44(A), conduit installed on the coldest day would expand about 4" per 100' on the hottest day.

 

[bphgravity]

Length of run is only one half of the equation when considering expansion/contraction characteristics of RNC conduit. The main issue is temperature. Expansion or contraction can occur at very short lengths of conduit if the temperature change is very high, and no length change may occur if the temperature remains low and does not change dramatically.

Also remember that most expansion fittings have instructions that indicate a 30?F factor must be added to highest ambient temperature where exposed to direct rays of the sun.

For example, assume a 50' run of RNC in direct sunlight with a maximum expected temperature of 95?F and minimum likely temperature of 25?F:

95? + 30? - 25? = 100?F temperature change. Per Table 352.44(A), this would produce a change in conduit length of 4.06 in / 2 = 2.03 in.