Conduits inside Conduit

Not clear on what your up to.
How about a wireway with dividers.
Need to design entry and how to terminate or end the run. Maybe a custom pullbox with a partial removable cover and one fixed portion to mount your outlet.
 
MyCleveland said:
Not clear on what your up to.
How about a wireway with dividers.
Need to design entry and how to terminate or end the run. Maybe a custom pullbox with a partial removable cover and one fixed portion to mount your outlet.
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My OP describes what's being proposed. However, instead of the small conduits it was recommended in later posts to use innerduct.
 
Grouch1980 said:
I've never specified innerduct, so this would be a first for me.
Is this it?: https://innerduct.com/corrugated/

How does this work? The AC wiring would go in its own innerduct (instead of conduit), the DC in its own, and the communications wiring in its own innerduct as well? And then all 3 corrugated innerducts would be installed inside the large conduit? So this would eliminate all the small conduits, now replaced by innerduct?
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That is my understanding. You find a innerduct rated for the application and put in a 6" pipe. It could have been any piping. Most of the time I think I see PVC used. There is one set in 6" EMT in the building I work in. Used for mixture of lighting and communication. But adding in the DC 2000V cable shouldn't make it more complicated. So long as the conductors aren't too large.

You pull in all the innerduct with pull tape at the same time (or that was how it was explained to me when I was drafting plans). Then they use the pull tape to pull the conductors through. In 6in conduit we have put 4-1" innerduct conduits. The cables would have to fit inside the innerduct conduit for fill consideration.

I was just trying to answer the question for you. I have never tried to design it the way you wrote it. But I do think it would be possible this way.
 
Elect117 said:
That is my understanding. You find a innerduct rated for the application and put in a 6" pipe. It could have been any piping. Most of the time I think I see PVC used. There is one set in 6" EMT in the building I work in. Used for mixture of lighting and communication. But adding in the DC 2000V cable shouldn't make it more complicated. So long as the conductors aren't too large.

You pull in all the innerduct with pull tape at the same time (or that was how it was explained to me when I was drafting plans). Then they use the pull tape to pull the conductors through. In 6in conduit we have put 4-1" innerduct conduits. The cables would have to fit inside the innerduct conduit for fill consideration.

I was just trying to answer the question for you. I have never tried to design it the way you wrote it. But I do think it would be possible this way.
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Aside from being easier to install conduit within conduit... does innerduct alleviate any heat build up?
 
Grouch1980 said:
Aside from being easier to install conduit within conduit... does innerduct alleviate any heat build up?
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Someone would have to use etap or similar modeling software to check it.

There is the possibility it does and the possibility it doesn't.

The heat from a loaded cable in innerduct would act the same way as a duct bank. Where a duct bank is in earth the innerduct is not spaced and is in (more or less) stale air. I would assume it is better than if all those cables were directly touching. I would also assume that it is worse than if you were to put each circuit in their own conduit and mount them with separation in free air.
 
Elect117 said:
Someone would have to use etap or similar modeling software to check it.

There is the possibility it does and the possibility it doesn't.
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I keep thinking it's similar to the conduits being in a tight wall cavity. Could heat build up more than in a wall cavity?
 
2020 NEC 310.15(C)(2) has the blanket requirement "Spacing between raceways shall be maintained."

Is it correct to say that an innerduct installation does not comply with 310.15(C)(2), and therefore at most one of the innerducts may be used for a Chapter 3 wiring method?

Cheers, Wayne
 
Grouch1980 said:
I keep thinking it's similar to the conduits being in a tight wall cavity. Could heat build up more than in a wall cavity?
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As a practical realistic matter, IMHO no.

As a code matter, maybe.

Consider that code requires the exact same derating for 9 #12 CCCs in a 1/2 EMT, as for those same 9 #12 CCCs in a 6" GRC. Obviously heat is less of a factor in the second case, but code makes no allowance for this.

If you have three sets of conductors in three code compliant raceways, but they are then all in a sleeve that is itself a raceway, then I don't know what code says about derating.

Jonathan
 
wwhitney said:
2020 NEC 310.15(C)(2) has the blanket requirement "Spacing between raceways shall be maintained."

Is it correct to say that an innerduct installation does not comply with 310.15(C)(2), and therefore at most one of the innerducts may be used for a Chapter 3 wiring method?

Cheers, Wayne
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I think that is just saying that adjustment factors are required and should be considered if the conduits aren't spaced. But it also doesn't say what the spacing is. Can they touch? lol.

I think (C)(2) is just saying that raceways that are spaced right don't need adjustment. Like if you had 2 CCCs, you wouldn't need to read (C)(1). You also have a sentence in (C)(1) that points to conductors of different systems in a common raceway. So they might consider the larger conduit the raceway you would do the derating with.


Grouch1980 said:
I keep thinking it's similar to the conduits being in a tight wall cavity. Could heat build up more than in a wall cavity?
Click to expand...

You might need a modeling program. I can't answer that. I personally treated it like a duct bank and someone else did the modeling for ampacity adjustments.
 
Grouch1980 said:
Aside from being easier to install conduit within conduit... does innerduct alleviate any heat build up?
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I would think not as the smaller conduit is encapsulated within another larger conduit with other mixed usage innerduct holding in the heat and actually heating the low voltage communication cables duct depending on the heat generated. Only way it would is if the outer conduit had open air flow or forced air flow though the outer conduit cooling the inner conduits.
 
Elect117 said:
I think that is just saying that adjustment factors are required and should be considered if the conduits aren't spaced. But it also doesn't say what the spacing is. Can they touch? lol.
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References 2023 NEC

800.133(B) Other Applications.
Communications wires and cables and CATV-type coaxial cables shall be separated at least 50 mm (2 in.) from conductors of any electric light, power, Class 1, non-power-limited fire alarm, or medium-power network-powered broadband communications circuits.

(Hard pressed to see how this can be complied with when inside another conduit with current carrying conductors.)

310.15(C)(2) Raceway Spacing.
Spacing between raceways shall be maintained.
(Whatever that really means. Other than they can't touch or cross. Not sure how it would be accomplished with flexible conduit within another conduit. )

300.3(C) Conductors of Different Systems.​

(1) 1000 Volts ac, 1500 volts dc, Nominal, or Less.​

Conductors of ac and dc circuits rated 1000 volts ac, 1500 volts dc, nominal, or less shall be permitted to occupy the same equipment wiring enclosure, cable, or raceway. All conductors shall have an insulation rating equal to at least the maximum circuit voltage applied to any conductor within the enclosure, cable, or raceway.
Secondary wiring to electric-discharge lamps of 1000 volts ac, 1500 volts dc, or less, if insulated for the secondary voltage involved, shall be permitted to occupy the same luminaire, sign, or outline lighting enclosure as the branch-circuit conductors.
 
Grouch1980 said:
Aside from being easier to install conduit within conduit... does innerduct alleviate any heat build up?
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How could it? Heat once generated has to conduct to the outside. The more layers, the more barriers and thermal resistance.

What would help is chopping the outer-duct for ventilation, or using steel. If all the conductors are encapsulated inside, then the outterduct is just a raceway, like a cable tray, no?
 
wwhitney said:
2020 NEC 310.15(C)(2) has the blanket requirement "Spacing between raceways shall be maintained."

Is it correct to say that an innerduct installation does not comply with 310.15(C)(2), and therefore at most one of the innerducts may be used for a Chapter 3 wiring method?

Cheers, Wayne
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I found this thread regarding an explanation from Charlie on "spacing between raceways shall be maintained"... go to Post #6. Seems like conduits can actually touch.

Seperation of conduits in trench

Is there any code, building, NEC or otherwise that calls for seperation of PVC conduit being buried in a trench for low volt runs, fire, alarm, telephone, cable? On the same note is there any code that calls for seperation of 120/208/240/277 runs in PVC in a ditch? I couldn't find anything...
forums.mikeholt.com

Elect117 said:
I think that is just saying that adjustment factors are required and should be considered if the conduits aren't spaced. But it also doesn't say what the spacing is. Can they touch? lol.
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Fred B said:
310.15(C)(2) Raceway Spacing.
Spacing between raceways shall be maintained.
(Whatever that really means. Other than they can't touch or cross. Not sure how it would be accomplished with flexible conduit within another conduit. )
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So if conduits can touch, and the NEC doesn't mention derating factors... then you don't have to derate?
 
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