cable tray clarification.

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69gp

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Just looking for an opinion if cable tray would be considered a raceway? article 100 definitions says that a raceway is enclosed. So does that mean an open cable tray is not a race way but that if the cable tray has a cover it is then considered a raceway?

thanks in advance
 
I am trying to determine if an expansion fitting is required by code when crossing a a rooftop expansion joint. If it was RGS, EMT or a similar wiring method then it is definitely required. The photo below shows a cable tray crossing over a rooftop expansion with no provisions for a expansion fitting in the tray. There are expansion fittings in the cable tray but not at the building expansion joint. The cable tray shown in the picture is going to have a cover installed over it.

I have seen where cable tray not properly installed will self destruct if not properly installed. My opinion says that a expansion fitting is required. But I am unable to find anything in the code to back this up.

Cable tray SSB.jpg
 
As Smart stated cable tray is not a raceway and is considered a support system by the NEC.


392.2 Definition.Cable Tray System. A unit or assembly of units or sections
and associated fittings forming a structural system used to
securely fasten or support cables and raceways.
II. Installation
392.10 Uses Permitted. Cable tray shall be permitted to be
used as a support system for service conductors, feeders,
branch circuits, communications circuits, control circuits,
and signaling circuits.
Click to expand...
 
infinity said:
As Smart stated cable tray is not a raceway and is considered a support system by the NEC.
Click to expand...


I understand the definition at this point. My question now is around if an expansion fitting is required for the cable tray as it passes over a roof expansion joint.
 
69gp said:
I understand the definition at this point. My question now is around if an expansion fitting is required for the cable tray as it passes over a roof expansion joint.
Click to expand...
There's nothing in Code which specifically requires a cable tray expansion joint let alone its exact placement.

Structurally speaking, even if a slip joint is required because of a structural expansion joint, it does not have to be directly in line with the structural expansion joint. Anywhere between two unyielding securements will suffice. Nonetheless, where the most flexure will occur is the best location. :D
 
69gp said:
I understand the definition at this point. My question now is around if an expansion fitting is required for the cable tray as it passes over a roof expansion joint.
Click to expand...


IMO the NEC would require the EJ for a raceway but not a support system.
 
Smart $ said:
Nonetheless, where the most flexure will occur is the best location. :D
Click to expand...

I disagree. You usually want breaks in continuity to occur where the bending stress is as little as possible. This generally is at the 1/4 & 3/4 points along the span.

But it is true that for axial flexibility, you want it in the span that crosses an expansion joint.
 
69gp said:
I am trying to determine if an expansion fitting is required by code when crossing a a rooftop expansion joint. If it was RGS, EMT or a similar wiring method then it is definitely required.
Click to expand...

What NEC code section would definitely require that?
 
qcroanoke said:
I feel like this is a setup but here goes:
300.7(B)
352.44
355.44
366.44
368.244
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2014 NEC?

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

When 'is necessary' who decides?

352.44, 355.44, 366.44, 368.44 are all methods the OP did not mention.

The OP specified EMT or GRC.
 
iwire said:
2014 NEC?



When 'is necessary' who decides?

352.44, 355.44, 366.44, 368.44 are all methods the OP did not mention.

The OP specified EMT or GRC.
Click to expand...

Actually 2017.
Is Massachusetts under 2017 now? But it does say where necessary.
"Raceways shall be provided with expansion, expansion-deflection or deflection fittings where necessary to compensate for thermal expansion, deflection and contraction."


"69gp


"I am trying to determine if an expansion fitting is required by code when crossing a rooftop expansion joint. If it was RGS, EMT or a similar wiring method then it is definitely required."

so, no, he said similar wiring method also. :)
 
iwire said:
What NEC code section would definitely require that?
Click to expand...
300.4
(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...
 
Smart $ said:
300.4
Click to expand...

This applies to raceways and since cable tray is not considered a raceway this would not apply..

My thing is that aluminum expands more than steel and the tray is almost the same as a raceway and should in my opinion follow the same guidelines as conduit where it crosses over a building expansion joint. If an expansion fitting is not installed its either the cable tray getting damaged or the roof membrane being damaged.
 
For a raceway method lack of a needed expansion joint could easily result in damage to conductors (or at least exposure of conductors). That is, IMHO, much less likely with a cable tray.
Failing to install a needed expansion joint in a cable tray can result in damage to the cable tray, but that may not be a matter for the NEC unless it is covered by the installation instructions.

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