HDPE & PVC Underground in Cold Environments

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deb4523

Member
Location
Alaska, USA
Does anyone have experience with HDPE or PVC Conduit in extreme weather environments?

I'm working on an outdoor project which will need conduit run (totally underground) in 30-40ft runs. The weather here fluctuates from -60F in winter (ambient temp) to +95F in summer. The ground freezes about 10 feet deep in the winter and we get frost heaving.

Can I expect the HDPE or PVC conduit to survive in an environment like this or should I go with RMC (or another alternative)? I read that they tend to do a lot of contracting and expanding with temperature changes and get very brittle when cold, so I'm thinking it isn't a good choice. Our soil here is not corrosive, so that isn't an issue for a metallic conduit....

Thanks!
 

deb4523

Member
Location
Alaska, USA
One more question: In some older installations of the same type, they show a single #4 bare copper counterpoise being run 6" above the conduit. This is just regular power for lights going through the conduit. Do I need to continue with the counterpoise? My impression is that counterpoise is mainly for communications towers, etc. Can anyone think why they would have run the counterpoise?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Does anyone have experience with HDPE or PVC Conduit in extreme weather environments?

I'm working on an outdoor project which will need conduit run (totally underground) in 30-40ft runs. The weather here fluctuates from -60F in winter (ambient temp) to +95F in summer. The ground freezes about 10 feet deep in the winter and we get frost heaving.

Can I expect the HDPE or PVC conduit to survive in an environment like this or should I go with RMC (or another alternative)? I read that they tend to do a lot of contracting and expanding with temperature changes and get very brittle when cold, so I'm thinking it isn't a good choice. Our soil here is not corrosive, so that isn't an issue for a metallic conduit....

Thanks!
Personally, I think PVC is not the greatest choice for such an environment but keep in mind if the PVC conduit breaks it probably won't have much affect on the conductors.

I don't have any experience with HDPE but suspect it would work better than PVC.

One more question: In some older installations of the same type, they show a single #4 bare copper counterpoise being run 6" above the conduit. This is just regular power for lights going through the conduit. Do I need to continue with the counterpoise? My impression is that counterpoise is mainly for communications towers, etc. Can anyone think why they would have run the counterpoise?
Lots of strange grounding requirements out there.
 
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