Expansion of 3" EMT On Roof

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gary

Senior Member
Location
California
Occupation
Retired electrical contractor / general contractor
Question I have (5) runs of parallel 3" EMT Conduits Each with (2) Sets of 400Kcm Alum & (1) #350 Gr Alum the run is 535 then 90Deg 35' for a total of 570' this run uses Cooper B-line Dura-Blocks for support on the roof at 8' apart 6" off of roof 3 x 3 x 12 on each end, My Inspector is requesting Expansion Couplings, I have never heard of this on a roof and what would be the Calculation for this , the area is Ontario, Ca Max ASHRAE for this area is 98Deg F (2% Wet Bulb Summer , Can not find Winter ? Need Help:angel:
 

tom baker

First Chief Moderator
Staff member
See 300.7(B) for a IN on the expansion of metal raceways, including EMT. Its given in inches change per degree of temp change.
Determine the run and the temp change, and see what the total expansion. If more than 1/2" you may need exp joint just depends on when it expands will it damage a connection or box?
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
If the blocks allowed the 535 foot run to slide relative to the roof and the box or 90 could move sideways far enough to take up the expansion too, then no problem. But you have to at least do the calculation to determine that. And EMT mounted to a metal roof or metal structure on the roof will expand at the same rate as the support until you get to an expansion joint in the support.
It really does come down to whether something would be damaged.

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Mouser

Member
Location
Riverside, CA.
300.7

300.7

(B) Expansion Fittings. Raceways shall be provided with
expansion fittings where necessary to compensate for thermal
expansion and contraction.

Informational Note: Table 352.44 and Table 355.44 provide
the expansion information for polyvinyl chloride
(PVC) and for reinforced thermosetting resin conduit
(RTRC), respectively. A nominal number for steel conduit
can be determined by multiplying the expansion length in
Table 352.44 by 0.20. The coefficient of expansion for steel
electrical metallic tubing, intermediate metal conduit, and
rigid conduit is 1.170? 10?5 (0.0000117 mm per mm of
conduit for each ?C in temperature change) [0.650 ? 10?5
(0.0000065 in. per inch of conduit for each ?F in temperature
change)].
A nominal number for aluminum conduit and aluminum
electrical metallic tubing can be determined by multiplying
the expansion length in Table 352.44 by 0.40. The
coefficient of expansion for aluminum electrical metallic
tubing and aluminum rigid metal conduit is 2.34 ? 10?5
(0.0000234 mm per mm of conduit for each ?C in temperature
change) [1.30 ? 10?5 (0.000013) in. per inch of conduit
for each ?F in temperature change].
 
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