Conduit fill with conduit in conduit

[exp]

In general it’s not allowed to run low-voltage wiring along with line voltage in the same conduit. However, it seems to be permissible to put another conduit in the conduit through which to run the low voltage wiring.

Example: 1-1/4 EMT with 3 THHN wires and one 1/2 ENT. Through the ENT Ethernet.

How does conduit fill work in this case?

Here is my attempt: 1-1/4 EMT has 1.23sqin cross section. 1/2 ENT has 0.196sqin.

Now I subtract them and the remaining area in the EMT is 1.031sqin which corresponds to 1.15” diameter. Round down to an 1” EMT. In a 1” EMT I could run up to four AWG4 THHN copper.

Is that right?

 

[letgomywago]

Only time I'd every consider anything like this would be a sleave in a concrete wall.

They do this with directional boring but there's more too it like doing 2 separate conduits inside a main sleeve.

They make direct bury lv cable that'd only need to be 6 in deep I'd go that route way before any of these shenanigans

 

[exp]

Do you mean a penetration wall SLEEVE?

This is actually very close to my application. But through stucco wall, and then 2-3 ft on exterior wall.

Anyway, as a general question, I’m interested in how conduit fill would even work in such a “shenanigan” case

 

[winnie]

I would think you'd need to consider the outer cross section of the inner conduit, and you need to calculate the outer cross section using the largest OD of the inner conduit.

You would also need to ensure that the outside of the inner conduit is suitable for pulling wire against.

1/2 ent has an outer diameter of 0.84" and an outer cross section of 0.554 sq. in. 4x #4 THHN + 1x 1/2 ENT in 1-1/4 ENT gives a conduit fill of 58%, and is a no go except for a sleeve up to 24" long.

The Southwire conduit fill calculator let's you add 'user defined' wires to the calculation, so you can check arbitrary wire combinations.

Jon

 

[letgomywago]

Do you mean a penetration wall SLEEVE?

This is actually very close to my application. But through stucco wall, and then 2-3 ft on exterior wall.

Anyway, as a general question, I’m interested in how conduit fill would even work in such a “shenanigan” case

Yes auto correct failed me a sleeve. If you're doing this in stucco why not just cut a new hole

 

[exp]

Hi Jon, thank you!

So the calculation like this would be correct?




These followup questions:

1.)

You would also need to ensure that the outside of the inner conduit is suitable for pulling wire against.

How would one figure that out?

2.) It seems 1/2 ENT is the smallest diameter I can find. Is there any other tubing with smaller diameter that would be permissible? What exactly defines (NEC reference preferred) which tubing could be put into EMT along with line voltage AND run SELV inside the tubing? There is for example "CHICAGO ELECTRIC 3/8 in. Protective Wire Wrap". I assume this would NOT be allowed, but based on which NEC section?

 

[winnie]

That is the calculation I did.

Regarding the outside being suitable for pulling against, I'd think any NM conduit without sharp edges would be fine.

Regarding a smaller suitable conduit, I have no suggestions.

-Jonathan

 

[winnie]

If the wall penetration portion is <24" long, then you might be able to use the 'sleeve' rules which allow for 60% fill.

For the outside run, use a larger (or separate) conduit.

Transition in a suitable box inside and outside

 

[mikeames]

In general it’s not allowed to run low-voltage wiring along with line voltage in the same conduit. However, it seems to be permissible to put another conduit in the conduit through which to run the low voltage wiring.

Since you specified ethernet.

You can with the appropriate cable (Class1). You have to take performance characteristics into considerations. Here's a product for example. https://www.panduit.com/content/dam/panduit/en/products/media/7/87/887/9887/110149887.pdf

 

[MacG]

I am curious how you're terminating the inner conduit and handling the mix of lv and line in the same box.

 

[exp]

I am curious how you're terminating the inner conduit and handling the mix of lv and line in the same box.

Assuming conduit fill passes etc, I would connect the inner tube on a junction box with proper fittings. Then the one LV knockout is a “tunnel” that never comes in contact with a line voltage section. IMO this should be compliant, but do not have reference.

Since you specified ethernet.

You can with the appropriate cable (Class1). You have to take performance characteristics into considerations. Here's a product for example. https://www.panduit.com/content/dam/panduit/en/products/media/7/87/887/9887/110149887.pdf

This is amazing! Can you confirm/clarify that the Ethernet could even be brought outside of the conduit enclosure? With a proper bushing on a metal junction box for example?

 

[mikeames]

I don't know, I have not used it. Their page is here.

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