Conduit inside of other conduit

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TravisA76

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Portland, OR, USA
Another engineer and I have been discussing an installation under construction. There is a need to run two lighting circuits to a shelter about 100 feet away. One circuit is on normal power and the other is UL 924 emergency. It seems to me that the best solution is to run two raceways underground to the shelter and then transition to LFMC for running inside the structural steel of the shelter. The other engineer has proposed running a 2" steel conduit underground to the shelter with (2) 1/2" LFMCs (and a bare copper ground conductor) inside of this steel conduit. Has anyone seen this type of installation before? It isn't apparent to me that it is code compliant, but I can't see that the code necessarily prohibits it either.
 
I don't see any code or real world issues with putting the LFMC in a sleeve, however I doubt that would be a cost effective installation as compared to two conduits.
 
I see no problem running 'conduit in conduit'. The inner conduit is the one that meets code, the outer conduit is simply a mechanical enclosure.

Is running _two_ circuits to a detached structure itself a problem?

-Jon
 
TravisA76 said:
The other engineer has proposed running a 2" steel conduit underground to the shelter with (2) 1/2" LFMCs (and a bare copper ground conductor) inside of this steel conduit. Has anyone seen this type of installation before?
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No, and, thank goodness.... :happyno:


JAP>
 
I have seen this in residential settings, sort of. Usually it's the 4" (or smaller) sleeve run under a driveway with a gate circuit, landscape cable, pool circuit, etc.

Any reason why you can't run PVC? Little bit cheaper to use...
 
I agree with Don, its a lot of fussing around to get conduits inside a conduit. And if you use say, 4" PVC water pipe, in the future, someone digging says, hey no problem its a water pipe, we'll cut and repair. Opps what are those conduits and wires in there!!!
 
I don't see a problem with this. We've even intentionally designed this before. One case is where you've got an existing oversized raceway and there is need to maintain seperatation (for whatever reason) between two different sets of cables. Conduit/flex goes inside the existing raceway. Where seperation is desirable but not required, my preference is to use fabric-type innerduct. In your case, though, I'd certainly prefer just two conduits by themselves.
 
Thank you

Thank you

Thank you for your responses. After discussing with the contractor, it was decided to run two separate 1-1/4" PVC conduits underground to the shelter, each with one 1/2" LFMC and separate bare ground wire.
 
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