# Underground conduits / duct seal



## TOOL_5150 (Aug 27, 2007)

Had an inspector say today "Id like to see that underground conduit sealed with duct seal" I just kind of noddded and was going to see if she was going to put it on the permit to be done before final. She didn't so I didnt have to fight it, but it got me wondering: Is it required anywhere in the NEC, other than classified locations, to seal underground conduits?

~Matt


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## leland (Dec 28, 2007)

TOOL_5150 said:


> Had an inspector say today "Id like to see that underground conduit sealed with duct seal" I just kind of noddded and was going to see if she was going to put it on the permit to be done before final. She didn't so I didnt have to fight it, but it got me wondering: Is it required anywhere in the NEC, other than classified locations, to seal underground conduits?
> 
> ~Matt



Will be Next month. 2011


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## TOOL_5150 (Aug 27, 2007)

leland said:


> Will be Next month. 2011


got a ref? California is just going to 2008 jan1


~Matt


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## manchestersparky (Mar 25, 2007)

before giving an answer, we need to know what the conduits were terminated to, and where they were run and so forth.

Look into article 300.5 (B) and then 300.5(4)(G) in the 2008 NEC.

300.5(B) tells you that a conduit under ground is a wet location.
300.5(4)(G) tells you to plug the end(s) of conduits if the conduit can introduce moisture to live parts.


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## raider1 (Jan 22, 2007)

TOOL_5150 said:


> got a ref? California is just going to 2008 jan1
> 
> 
> ~Matt


Check out 225.27 in the 2011 NEC.



> *
> 225.27 Raceway Seal.​*​​​​Where a raceway enters a building
> or structure from an underground distribution system, it
> shall be sealed in accordance with 300.5(G). Spare or unused
> ...




Also this has been required for services for awhile.

Check out 230.8.

Chris


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## Podagrower (Mar 16, 2008)

Well, while we are talking about it...
I've always (mostly) sealed conduits that exited the building, service entrance, exterior lighting, AC compressors, etc. I did a job last year where the inspector said all the conduits under the slab left the building, so they all needed to be sealed. It wasn't worth arguing (maybe 30 1" homeruns), so I just did it.
So, do the pipes under the slab leave the building? Or is everything inside the footer inside the building?


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## TOOL_5150 (Aug 27, 2007)

The conduit went from a bell box on a detached structure, underground, then back up into the bottom of a 10x10 3R that was on the house. There was no way water would leak into either of the boxes.

~Matt


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## TOOL_5150 (Aug 27, 2007)

raider1 said:


> Check out 225.27 in the 2011 NEC.
> 
> 
> 
> ...




EVen under 2011, this would not apply - its not an underground distribution system.

~Matt


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## leland (Dec 28, 2007)

TOOL_5150 said:


> Had an inspector say today "Id like to see that underground conduit sealed with duct seal" I just kind of noddded and was going to see if she was going to put it on the permit to be done before final. She didn't so I didnt have to fight it, but it got me wondering: Is it required anywhere in the NEC, other than classified locations, to seal underground conduits?
> 
> ~Matt



Now that you expanded this... No need to seal.


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## Southeast Power (Jan 18, 2009)

For some reason, we put ductseal on conduits ONLY for underground services.
I usually put duct seal in conduits that come inside from generators. An air exchange sometimes develops when the unit comes on.


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## joebanana (Dec 21, 2010)

AHJ. I did a power gen. plant a few years back, and all u/g vault conduits had to be sealed because of the rats. They'd use the 4"'s for a drive thru dinner. They can digest THHN/THWN, and SIS, but not duct seal.


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## one2question (Sep 2, 2010)

I have seen water fill up storage rooms because they where not sealed. Below the water table.


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## B4T (Feb 10, 2009)

Goose poop would do a better job of keeping water out of conduits..

There are millions of compression water tight connectors on services that rely on duct seal to keep the water out.

We all know how good that is working, but it does generate some nice dollars.. :thumbsup:


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## Peter-D (Dec 22, 2010)

B4T said:


> Goose poop would do a better job of keeping water out of conduits..


Would Scotchkote do a better job? :laughing:


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## thegoldenboy (Aug 15, 2010)

We do a lot of traffic intersections for the company I work for. It's usually 3" Sch. 80 underground with concrete handholes every 150' or thereabouts and after we pull the wire in we go behind and put a duct seal patty over the ends of the pipe in the handholes. I've only personally done it once but the traffic foreman told me it was more of a state requirement than a NEC requirement. 

The job I was on this summer, I think we used spray foam and duct seal when the lateral came into the CT cabinet. I didn't work on it myself but I'm pretty sure what that's what the guy used to seal it up.


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## macmikeman (Jan 23, 2007)

Duct seal looks pretty. Expanding foam works better. Take your pick.


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