Underground Rigid Metal Conduit

Grouch1980

Senior Member
Location
New York, NY
Hi all,
In an application where you bury RMC conduit, at least 5 feet away from an in-ground pool (I'm looking at 2008 NEC section 680.10), the section states that the metal conduit shall be "corrosion resistant and suitable for the location". What about the RMC couplings? are these considered water proof, or could water potentially seep into the conduit? I went through some past threads, I couldn't find this exact question though.

Thanks!
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
RMC is not designed to be or required to be waterproof. Even PVC with glued joints will retain water due to condensation within the buried raceway. RMC with standard fittings can be buried in normal soil conditions without extra protection beyond the galvanized coating. NYC is still under a modified version of the 2008 NEC but 5' underground separation rule for pools has been removed.
 

Grouch1980

Senior Member
Location
New York, NY
Thanks guys. I guess I could specify on the drawings for water-tight seals to be applied to the coupling areas? It's the client bringing up worries. What type of seal would I specify? is it some sort of spray on material?
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Thanks guys. I guess I could specify on the drawings for water-tight seals to be applied to the coupling areas? It's the client bringing up worries. What type of seal would I specify? is it some sort of spray on material?
You could spray or paint on some material but it won't stop the RMC from retaining water. IMO it may be better not to seal it at all because the condensation within the raceway will eventually leak out through the couplings.
 

Strathead

Senior Member
RMC is not designed to be or required to be waterproof. Even PVC with glued joints will retain water due to condensation within the buried raceway. RMC with standard fittings can be buried in normal soil conditions without extra protection beyond the galvanized coating. NYC is still under a modified version of the 2008 NEC but 5' underground separation rule for pools has been removed.
And yet all fittings are required to be "listed for use in wet locations" per 314.15. I believe a threaded coupling is a fitting. I am dealing with this right now with regards to threadless couplings. This code is BS. Since the NEC even states the inside of a conduit run outdoors is considered a wet location, why do the fittings need to be listed? Regards EMT as well. Not a well thought out code.
 

jap

Senior Member
You could spray or paint on some material but it won't stop the RMC from retaining water. IMO it may be better not to seal it at all because the condensation within the raceway will eventually leak out through the couplings.

Agreed.

For what it's worth I buried a 15' run of 1" galvanized rigid between my house and garage to feed my garage panel about 25 years ago because that's what I had at the time.

Thought it'd last a lifetime before I knew any different.

I was digging up for a sidewalk pour recently and found that it was completely destroyed.

Mostly nothing more than the Thhn conductors left.

Needless to say, my garage feeder is in 1" Pvc now. :)

JAP>
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Agreed.

For what it's worth I buried a 15' run of 1" galvanized rigid between my house and garage to feed my garage panel about 25 years ago because that's what I had at the time.

Thought it'd last a lifetime before I knew any different.

I was digging up for a sidewalk pour recently and found that it was completely destroyed.

Mostly nothing more than the Thhn conductors left.

Needless to say, my garage feeder is in 1" Pvc now. :)

JAP>
There are certainly some soil conditions that might make UG installation of metallic raceways inappropriate.

Personally, I would use PVC for anything UG, just for the ease of install and cost benefit. The only thing I can see where rigid UG makes sense is that you don't have to bury it as deep as PVC or DB cable and some areas that might matter.
 
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