Conduit type for underground 90 deg riser (PVC vs Rigid)

P

philly

Senior Member
Trying to get a gauge for what most people use/specify for underground 90 deg risers with PVC conduit routing. Applicaiton I'm specifically referring to is PVC conduit routed underground that then transitions 90degress to above grade for bottom entry into foundation/enclosure, or continues above grade as transition to overhead routing.

I have seen some applications where 90's are PVC to match conduit run and others where rigid 90's are specific. Justification for rigid 90's that I have seen is usually related to PVC 90's being prone to damage/failure from burn during pull.

Does anyone use PVC coated rigid (Ocal) for these underground 90's?

Appreciate any experiences or typical approach for applications that others have seen.
 
Yes, we used to specify PVC-coated RGS conduit for 90s in underground PVC conduit. For the transition from PVC to exposed, we also specified PVC-coated RGS for the most part. The PVC coating is to deal with corrosion. We were doing a lot of wastewater treatment facilities and there could be issues with hydrogen sulfide and other chemicals. The corrosion usually occurs right at the interface between the slab (or dirt) and the air, so some designers would just wrap the regular hot-dipped RGS with tape just in this area. I don't know how effective all this was over the long run, but we specified a lot of PVC-coated RGS.
 
I have installed a lot of PVC coated Rigid in paper mills and other industrial settings but it was above ground. IMO using it underground is wasted expense both material and labor wise. I could see using it for underground 90's but we just used rigid 90's
 
I did maintenance at a WWTP that plant was built in 85. They used rigid nipples up out of the slab, the rigid had extensive corrosion. I would use coated nipples at the concrete, either rigid or coated rigid above
Below you could use a regular rigid 90 and then go to PVC
If mule tape is used for pulling then there is no burn thru if 90s
With WWTPs you have one chance to get it right. Those plants are around for a long time!
 
I rarely address general construction materials but suggest considering Article 355 RTRC. It has excellent burn-through characteristics. We used several thousand feet for shore to ship power at major West Coast ports where it was often in direct contact with sea-water and it offered excellent corrosion resistance. Mechanically it compares favorably with RMC. Sweeps can be factory manufactured or field bent. It ain't cheap, but it doesn't cost quite as much as rigid steel either. There are several raceway interface fittings available. It can be used in several classified location applications - See Section 501.10(B)(1)(6).

Possible downsides are it can't be used as EGC. It may technically create some "Effective Ground-Fault Current Path" problems, particularly where entering metallic enclosures.

I don't market for manufacturers so search online for "rtrc conduit" and evaluate for yourself.
 
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