Conduit in a conduit

[David Hinton P.E.]

Got a unique question from my boss. He wants to know if you can run HDPE (Article 353) inside a larger size Rigid (Article 344) conduit in order to separate control wiring from power wiring for a generator set. Specifically, he wants to mix in the same conduit the power and control wiring (in HDPE) for a building's back-up generator. The HDPE would separate the control wiring from the power wiring. Can this be done? Comments?

 

[petersonra]

Don't they make a product specifically for doing just this?

353.10 Uses Permitted. The use of HDPE conduit shall be
permitted under the following conditions:
...
(5) Above ground, except as prohibited in 353.12, where
encased in not less than 50 mm (2 in.) of concrete.

353.12 Uses Not Permitted. HDPE conduit shall not be
used under the following conditions:
...
(2) Within a building

I think as long is it is outside and either underground or in concrete you might be OK.

 

[A/A Fuel GTX]

Why not use conductors with high enough voltage ratings to be installed together in the same conduit?

 

[fmtjfw]

Think ENT echo nemo tango

 

[A/A Fuel GTX]

Why not use conductors with high enough voltage ratings to be installed together in the same conduit?

Guess I should have asked what the supply voltage from the generator was before I made my comment.

 

[don_resqcapt19]

Why not use conductors with high enough voltage ratings to be installed together in the same conduit?

In many cases that will not help. It is often a code violation to run the control conductors in the same raceway as the power conductors even if all of the conductors have the same voltage rating.

 

[A/A Fuel GTX]

In many cases that will not help. It is often a code violation to run the control conductors in the same raceway as the power conductors even if all of the conductors have the same voltage rating.

I was using 300.3(C)(1) as my reference, Don. This wouldn't apply to a generator and it's control wiring?

 

[dicklaxt]

My first question would be how are you going to terminate the inner conduit,how are you going to gain access to fittings on the inner conduit,how are you going to pull wire in the inner conduit etc etc. You would probably spend more in labor to make this work than the price of a 2nd conduit.

I personally don't think this is a good design approach .I have never seen or heard of this being done unless the outer conduit is just a sleeve for long a span support.

I don't know if it is legal or not by the code but it certainly is unorthodox.

dick

 

[Dennis Alwon]

I was using 300.3(C)(1) as my reference, Don. This wouldn't apply to a generator and it's control wiring?

Depends on what class wiring it is. Look at 725.136(A)

 

[A/A Fuel GTX]

Depends on what class wiring it is. Look at 725.136(A)

I'd say the control wiring for a generator would fall under class 1 and be allowed with the supply conductors as long as the insulation was adequate.

 

[dicklaxt]

The physical parameters I was always held to in industrial design was the mixture of power and control conductors was not allowed when the power conductor was larger than #2.The reasoning behind this was the smaller conductors could get jammed and insulation skinned/ripped loose when pulling especially around bends when they got sandwiched in by the larger conductors.

There was also a break when the user end was greater than 50hp/kw.

I believe this was a design practice industry wide and not a code dictate.

dick

 

[tom baker]

I was using 300.3(C)(1) as my reference, Don. This wouldn't apply to a generator and it's control wiring?

You are missing the note at the end of that section.

 

[Flex]

if there are DC battery charger wires, wouldnt they have to be seperate?

 

[fmtjfw]

Nope

Nope

if there are DC battery charger wires, wouldnt they have to be seperate?

300.3 Conductors.
(C) Conductors of Different Systems.
(1) 600 Volts, Nominal, or Less. Conductors of ac and dc circuits, rated 600 volts, 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.

 

[fmtjfw]

ENT

ENT

Smurf tube (ENT) and its cousins are sometimes used in other conduits to separate cables, especially telecom stuff. ENT is allowed inside buildings (some rules for fire rating and place of assembly). It is pretty sturdy, I can jump up and down on it without breaking or deforming it. You could pull empty ENT with the power conductors into the main conduit, treating it as a single conductor of its outside diameter for fill purposes. It also comes as a prewired assembly. Consider:

725.136 Separation from Electric Light, Power, Class 1, Non?Power-Limited Fire Alarm Circuit Conductors, and Medium-Power Network-Powered Broadband Communications Cables.
(A) General. Cables and conductors of Class 2 and Class 3 circuits shall not be placed in any cable, cable tray, compartment, enclosure, manhole, outlet box, device box, raceway, or similar fitting with conductors of electric light, power, Class 1, non?power-limited fire alarm circuits, and medium-power network-powered broadband communications circuits unless permitted by 725.136(B) through (I).
(B) Separated by Barriers. Class 2 and Class 3 circuits shall be permitted to be installed together with the conductors of electric light, power, Class 1, non?power-limited fire alarm and medium power network-powered broadband communications circuits where they are separated by a barrier.
(C) Raceways Within Enclosures. In enclosures, Class 2 and Class 3 circuits shall be permitted to be installed in a raceway to separate them from Class 1, non?power-limited fire alarm and medium-power network-powered broadband communications circuits.

Calling a raceway an enclosure may be a little stretch.

100 Definitions.
Enclosure. The case or housing of apparatus, or the fence or walls surrounding an installation to prevent personnel from accidentally contacting energized parts or to protect the equipment from physical damage.

A raceway certainly performs the function of an enclosure.

 

[suemarkp]

This is commonly done in large conduits for fiber optics. Innerduct can be pulled through the conduit (in our building there are 3 innerducts per 3" or 4" conduit). I don't think Innerduct is a listed Chapter 3 NEC raceway, but it looks a lot like ENT to me except it is orange. The standard stuff is HDPE, but you may need the plenum or riser type to use it in a building.

 

[hurk27]

never understood the reasoning but buy a Generac home generator with a transfer panel (the one with breakers) and it will come with all conductors in the same conduit (flex) from the generator to the panel?

 

[dicklaxt]

It looks like a person(inspector) would be hard pressed to prove it could not be done but the other person(contractor) is still reading between the lines and leaning on the gray areas.

If you were the owner would you allow it ????????

I vote :thumbsdown: but I like my spaghetti to all run the same way on the plate,seriously ,what a hodge podge of an installation done by a professional.

dick

 

[fmtjfw]

This is commonly done in large conduits for fiber optics. Innerduct can be pulled through the conduit (in our building there are 3 innerducts per 3" or 4" conduit). I don't think Innerduct is a listed Chapter 3 NEC raceway, but it looks a lot like ENT to me except it is orange. The standard stuff is HDPE, but you may need the plenum or riser type to use it in a building.

That's why I suggested ENT, it is listed.

 

[fmtjfw]

never understood the reasoning but buy a Generac home generator with a transfer panel (the one with breakers) and it will come with all conductors in the same conduit (flex) from the generator to the panel?

It's probably listed as a single entity. If so the wiring in a listed device (think range, television, for instance) does not fall under NEC.