expansions

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rayertz

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I have a bank of overhead conduits leaving a plant going to a RTO equipment pad. Pad is about a 40' x 50' x 10' deep reinforced concrete. the conduit is 30' in length from the building until it turns a 90. Is an expansion required.

I am in Michigan. I looked up the expansion and found with a 100 degree swing in temp the expansion is about .75" in 100'. we are talking 30' so .25" expansion.

Your thoughts are welcome.
 
When the expansion exceeds 1/4" between fixed points an expansion fitting is required. It's calculated according to table 352.44. For 100° F the expansion for 100' of length is 4.06" or .0406"/ft. 30'*.0406=1.218" which exceeds the less than .25" allowance.


352.44 Expansion Fittings. Expansion fittings for PVC
conduit shall be provided to compensate for thermal expan-
sion and contraction where the length change, in accordance
withTable 352.44, 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.
Click to expand...
 
infinity said:
When the expansion exceeds 1/4" between fixed points an expansion fitting is required. It's calculated according to table 352.44. For 100° F the expansion for 100' of length is 4.06" or .0406"/ft. 30'*.0406=1.218" which exceeds the less than .25" allowance.
Click to expand...

Note that if the last 90 el is not firmly fastened but cantilevered off a support several feet down the vertical run, the provision above may not apply.
The interpretation of firmly fastened has to be taken in conjunction with the amount of expansion expected.
Some fastening situations, like the el I describe above, might allow 1/4" but not 2".
 
GoldDigger said:
Note that if the last 90 el is not firmly fastened but cantilevered off a support several feet down the vertical run, the provision above may not apply.
The interpretation of firmly fastened has to be taken in conjunction with the amount of expansion expected.
Some fastening situations, like the el I describe above, might allow 1/4" but not 2".
Click to expand...

I agree, it might require an "eyeball" from the inspector. Chances are that smaller PVC like 1/2"-1" would have a strap near the elbow since the supports must be no greater than 3' apart.
 
infinity said:
When the expansion exceeds 1/4" between fixed points an expansion fitting is required. It's calculated according to table 352.44. For 100° F the expansion for 100' of length is 4.06" or .0406"/ft. 30'*.0406=1.218" which exceeds the less than .25" allowance.
Click to expand...

This is rigid galvanized conduit. I do not see a table for RMC.
 
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