Conduit Sealing

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A/A Fuel GTX

A/A Fuel GTX

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Electrician
Is expanding foam acceptable for sealing conduits that transition from the outside to the inside, especially in the case of service entrance conductors, or is a product specifically designed for this purpose required?
 
A/A Fuel GTX said:
Is expanding foam acceptable for sealing conduits that transition from the outside to the inside, especially in the case of service entrance conductors, or is a product specifically designed for this purpose required?
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When changing enviornments, I think you might need a potting compound. MHO
 
It sure seems like the expanding foam would provide a better seal but I'm not sure about UL listing issues. That being said, the foam is used all the time to seal off penetrations where romex is changing environments in new construction.
 
I'm assuming that you're not talking about sealing off hazardous areas, so 300.50(E) calls for the conduit to be sealed with an 'identified compound' ... 'or it shall be so arranged to prevent moisture from contacting live parts.

Chapter 1 defines identified as "Recognizable as suitable for thespecific purpose, function, use, environment, application, and so forth where described in particular Code requirement."

My intrepretation would be no that you can not because expanding foam does not make a watertight seal. I know that underground conduits are never water tight, but the intent of the code is to prevent moisture ....

What do othes think?
 
A/A Fuel GTX said:
Correct. I'm talking about preventing cold air migrating into warm areas where condensation would be an issue.
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Are you talking around the conduit or in the end of a conduit? Underground run emerging inside, or not underground at all?

Regardless, of the preceding questions, the NEC does not make any substantial provisions on the material used for such. Traditionally, duct seal is used for inside the ends of conduit. Around the conduit is not governed by the NEC, so any commonly-used construction sealant for the type of penetration should suffice (even a DIY-type :mad::roll:)
 
Smart $ said:
Are you talking around the conduit or in the end of a conduit? Underground run emerging inside, or not underground at all?
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Possible scenarios would be:

Service entrance conductors in a conduit coming off the bottom of a meter socket, going into an LB and terminating in a loadcenter on an inside wall. I will usually seal off the conduit where it enters the building.

An underground feeder emerging from the ground, into an LB, entering the building and onward to the load. Here again, I will seal the conduit where it enters the building.
 
A/A Fuel GTX said:
Possible scenarios would be:

Service entrance conductors in a conduit coming off the bottom of a meter socket, going into an LB and terminating in a loadcenter on an inside wall. I will usually seal off the conduit where it enters the building.

An underground feeder emerging from the ground, into an LB, entering the building and onward to the load. Here again, I will seal the conduit where it enters the building.
Click to expand...
Around a conduit may require a fire-rated sealant. I am not certain of where, so I'll leave it at that.

If fire-rated sealant is not required, expanding foam would not be my first choice... at least not from a visible finish aspect. To fill gap I'd say it's okay, but I don't care for any "oozed-out" finished appearance. Trim it off when hardened and coat with caulk or something that mimics the exterior finish, and interior if readily visible in a finished area of the building. Yet this is just my opinion... no Code to back it up ;)
 
lakee911 said:
I'm assuming that you're not talking about sealing off hazardous areas, so 300.50(E) calls for the conduit to be sealed with an 'identified compound' ... 'or it shall be so arranged to prevent moisture from contacting live parts.
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The OP does not mention underground conduits, so 300.50 may or may not apply. He does mention transition from the outside to the inside, so I think 300.7(A) may be the more appropriate section. That section requires an "approved material to prevent the circulation of warm air to a colder section of the raceway or sleeve".

John25 said:
We use fiberglass insulation. There is usually some laying around the job site.
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I wouldn't approve that. Fiberglass insulation does slow down air movement, but it is not air tight.

As for the original question, I think the expanding foam does prevent air movement. So, unless underground conduits are involved, triggering 300.50, I would approve the expanding foam.
 
eprice said:
As for the original question, I think the expanding foam does prevent air movement. So, unless underground conduits are involved, triggering 300.50, I would approve the expanding foam.
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Why would 300.50 (E) change the picture? Wouldn't the expanding foam seal out moisture or gasses?
 
lakee911 said:
I'm assuming that you're not talking about sealing off hazardous areas, so 300.50(E) calls for the conduit to be sealed with an 'identified compound' ... 'or it shall be so arranged to prevent moisture from contacting live parts.

Chapter 1 defines identified as "Recognizable as suitable for thespecific purpose, function, use, environment, application, and so forth where described in particular Code requirement."

My intrepretation would be no that you can not because expanding foam does not make a watertight seal. I know that underground conduits are never water tight, but the intent of the code is to prevent moisture ....

What do othes think?
Click to expand...

Keep in mind that 300.50 only applies to systems over 600 volts.

300.5(G) applies to raceway seals of systems under 600 volts and does not require an identified compound.

Chris
 
eprice said:
The OP does not mention underground conduits, so 300.50 may or may not apply. He does mention transition from the outside to the inside, so I think 300.7(A) may be the more appropriate section. That section requires an "approved material to prevent the circulation of warm air to a colder section of the raceway or sleeve".



I wouldn't approve that. Fiberglass insulation does slow down air movement, but it is not air tight.

As for the original question, I think the expanding foam does prevent air movement. So, unless underground conduits are involved, triggering 300.50, I would approve the expanding foam.
Click to expand...

raider1 said:
Keep in mind that 300.50 only applies to systems over 600 volts.

300.5(G) applies to raceway seals of systems under 600 volts and does not require an identified compound.

Chris
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300.5(G) and 300.7(A) are referring to the inside of the conduit, not around the conduit.

The OP'er is asking about the gap left between wall members and raceway after penetrating an exterior wall. There is nothing in the NEC which covers this type of "sealing" other than...
300.21 Spread of Fire or Products of Combustion. Electrical
installations in hollow spaces, vertical shafts, and
ventilation or air-handling ducts shall be made so that the
possible spread of fire or products of combustion will not
be substantially increased. Openings around electrical penetrations
through fire-resistant-rated walls, partitions, floors, or ceilings
shall be firestopped using approved methods to maintain the
fire resistance rating.
FPN: Directories of electrical construction
materials published by qualified testing laboratories contain
many listing installation restrictions necessary to maintain
the fire-resistive rating of assemblies where penetrations or
openings are made. Building codes also contain restrictions
on membrane penetrations on opposite sides of a fireresistance-
rated wall assembly. An example is the 600-mm
(24-in.) minimum horizontal separation that usually applies
between boxes installed on opposite sides of the wall. Assistance
in complying with 300.21 can be found in building
codes, fire resistance directories, and product listings.
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Smart $ said:
300.5(G) and 300.7(A) are referring to the inside of the conduit, not around the conduit.

The OP'er is asking about the gap left between wall members and raceway after penetrating an exterior wall. There is nothing in the NEC which covers this type of "sealing" other than...

​
Click to expand...

I believe that the OPer was in fact talking about sealing the inside of a conduit.

Possible scenarios would be:

Service entrance conductors in a conduit coming off the bottom of a meter socket, going into an LB and terminating in a loadcenter on an inside wall. I will usually seal off the conduit where it enters the building.

An underground feeder emerging from the ground, into an LB, entering the building and onward to the load. Here again, I will seal the conduit where it enters the building.
Click to expand...

Chris
 
Sorry if I was not clear. I was talking about sealing the inside of a conduit. I always seal outside penetrations with silicone if the opening is small enough or expanding foam for irregular penetrations.
 
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