expansion conduit supports

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rayertz

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on a 700 foot trestle we have an expansion fitting every 60'. there is no expansion in the trestle itself. the question is how is the conduit supported between expansions.
Currently it is rigidly supported using right angle beam clamps (corn clamps). this leaves no room for conduit movement.
I read somewhere the conduit should be rigidly supported in the middle of the span then the supports between the middle to the expansions are like an over sized U-bolt used as a guide. the conduit is 1" GRC.
please advise. thanks for your guidance.
 
rayertz said:
yeah, it true. not 1 expansion in the trestle steel.
Click to expand...
There's no need for expansion joints in a run supported and/or secured to a structure of the same material, steel attached to steel in this case. You only need install expansion/contraction joint where there is a structural joint...

300.3 Conductors
...
(H) Structural Joints.A listed expansion/deflection fitting
or other approved means shall be used where a raceway
crosses a structural joint intended for expansion, contraction
or deflection, used in buildings, bridges, parking garages,
or other structures.
Click to expand...

...and if there aren't any, you only have to consider...

300.5 Underground Installations.
...
(J) Earth Movement. Where direct-buried conductors,
raceways, or cables are subject to movement by settlement
or frost, direct-buried conductors, raceways, or cables shall
be arranged so as to prevent damage to the enclosed conductors
or to equipment connected to the raceways.

Informational Note: This section recognizes “S” loops in
underground direct burial to raceway transitions, expansion
fittings in raceway risers to fixed equipment, and, generally,
the provision of flexible connections to equipment subject
to settlement or frost heaves.
Click to expand...
 
So on a 95 degree day, the hot sun beating on this 700' steel trestle has no affect on the structure.
We ran 13.8 feeders in conduit on an old railroad trestle last year. The trestle was 400' long, and on a hot day the expansion joints for the structure would absorb 2+ inches of lateral movement.

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