There are three types of PVC coated conduit; couplings are supplied separately.
- Primary PVC coating over bare steel which is a listed rigid conduit for environmentally suitable locations.
- A PVC coating over listed galvanized steel conduit. This is a supplementary coating intended for added protection in severely corrosive locations.
- A primary PVC coating over a supplementary coating of zinc. This is also intended for severely corrosive locations. These PVC-coated raceways are generally installed as a system, which means the fittings, conduit bodies, straps, hangers, boxes, etc., is also coated. There are, however, installations where only a coated elbow is used in a galvanized conduit run, such as where emerging from the soil or concrete. (NOTE: Manufacturers’ instructions are very important when installing PVC-coated products and systems, and special tools are generally required.)
To minimize installation damage to the PVC coatings, use tools specially designed for PVC coated conduit or standard tools that have been appropriately modified for installing PVC coated conduit. Standard tools which have not been modified could damage the coatings and shall not be used to install PVC- coated conduit. For repairing damage to the PVC coating.
Clamping (Vising) PVC-Coated Conduit
Various manufacturers offer modified jaws for use in standard vises to protect the coating. When using either a “jaw type” or a chain type” vise, the PVC-coated conduit can also be protected by half-shell clamps. These are available as a manufactured clamp or can be made in the field from RMC as follows.
Clamping sleeves made from steel RMC
- Make two half-shell pieces by first cutting two 6- inch pieces of standard conduit one trade size larger than the PVC-coated conduit to be clamped.
- Use a band saw to cut the 6-inch conduit sections lengthwise. Make the cut slightly off center. This creates two half shells, one smaller than the other.
- Discard the larger pieces and use the two smaller pieces to protect the conduit in the vise. Deburr any sharp edges. Properly made clamping sleeves will have a gap between the two pieces when positioned on the conduit.
- Where proper tooling for making a sleeve is not available, protect the PVC coating in the vise by wrapping the area to be clamped with sandpaper, emery cloth or cardboard. The coarse side of emery cloth or sandpaper should face the PVC coating. (NOTE: This is the least desirable method and should be avoided by planning ahead.
Cutting and Threading PVC-Coated Conduit
For full cutting and threading instructions for PVC coated conduit, contact the conduit manufacturer. The following provides general guidance.
Cutting and Reaming
Cutting with a saw is the preferred method. However, a roller cutter is acceptable providing the conduit is properly clamped.
Hand Threaders (Manual and Motorized)
If PVC-coated conduit is cut with a hacksaw or a band saw, and a hand-threader is used, trim the coating at an angle all the way around the conduit before threading. This is sometimes called pencil cut or bevel cut and enables the die teeth on the threader to engage the conduit. Be sure to follow the instructions in for clamping conduit, and ensure that the conduit is securely held in the vise.
A standard die head must be modified (machined) for use with PVC-coated conduit. To make this modification, the guide sleeve must be bored to allow the coated conduit to enter the die. The inside diameter must be increased by 110 mils (0.11 inch). (NOTE: The PVC coating shall not be removed to allow the use of standard non-machined die heads.)
Rotating machines with jaws that cut through the PVC coating shall not be used.
Long strips of metal or PVC from the threading can foul the die head and collapse the conduit. To avoid this and permit removal of PVC in small pieces, make a series of longitudinal cuts in the PVC coating (i.e., along the conduit) in the area to be threaded. The thread protector can be used as a length guide for the cuts.
Following the cutting operation, use a reamer to remove rough edges.
The NEC requires 300.6 that where corrosion protection is necessary and the conduit is threaded in the field, the thread shall be coated with an approved electrically conductive, corrosion-resistant compound. Coatings for this purpose, listed under UL category “FOIZ” are available. Zinc-rich paint or other coatings acceptable to the AHJ may be used. (NOTE: Corrosion protection is provided on factory-cut threads at time of manufacturing.)
Bending PVC- Coated Conduit
Manufactured elbows are available in a variety of radii. For field-bending, do the following:
Hand Bending of Small Conduit Sizes
To bend PVC-coated conduit, use an EMT bender one trade size larger than the conduit being bent. This is to avoid damaging the coating. For example, to bend trade size 3/4 PVC coated conduit, use a trade size 1 EMT bender.
Bending Coated Conduit
A bender with shoes made specifically to bend PVC-coated conduit is preferred. Otherwise, for trade sizes, 1/2 through 1-1/2, use an electric bender (see Figure 19) with EMT shoes one size larger than the PVC-coated conduit. A hand bender can also be used to bend the smaller trade sizes.
Trade sizes 2 and larger should be bent with a hydraulic bender.
Do not use lubricants on bending shoes.
Most manufacturers of hydraulic benders offer special shoes for PVC-coated conduit. Use these special shoes when possible.
If regular shoes are used, their sides must be modified to allow for the coating thickness. Some installers have done this by grinding or milling. Such modification is not recommended as it can create a safety hazard.