Taking installation precautions and using the proper tools impact performance significantly. Knowing these guidelines can help you prevent coating damage during installation.
With the exception of a few precautions necessary to protect the coating, PVC-coated conduit installation procedures are the same as those used to install standard galvanized conduit. While this industry recognizes the performance of PVC-coated conduit in corrosive environments, correct installation procedures to ensure performance are less widely known. Taking installation precautions and using the proper tools impact performance significantly, assuring the coating remains undamaged. Here's a list of precautions to prevent coating damage during installation.
Clamping. When using a pipe vise, replace the jaw assembly with special vise adapters. When using a chain vise for conduit diameters less than 2 in., wrap the clamp area with emery cloth (coarse surface against the coating). Use half-shell clamps to clamp 2 in. and larger diameter PVC-coated conduit. If you use a power unit that spins the conduit, equip the chuck with inserts designed for such conduit.
Cutting. You should cut the PVC-coated conduit with a roller cutter. This will make a square cut end and remove about quarter-inch of PVC coating, which aids in threading the conduit. You can use a hacksaw; however, this method requires a pencil cut so the die teeth engage the conduit.
Cutting away quarter-inch of the exterior coating in the same manner as sharpening a pencil allows the pipe guide to ride up and over the PVC coating, facilitates coating removal, and enables cutting the thread in one operation. You must use a reamer to remove any rough internal edges caused by cutting. This prevents insulation damage during wire pulling.
Threading. Before threading, make a series of cuts in the PVC along the longitudinal axis of the conduit. You can use the thread protector attached to the end of each conduit section to gauge the length of these cuts. These cuts help remove the PVC in small pieces rather than long strips, which can foul the die head. Before threading, machine the stationary guide to remove 0.120 in. so it can ride up and over the PVC coating. Always use a new die head, and never use the same one to thread rigid conduit.
After threading, clean the threads and conduit interior with a degreasing spray, to prepare for the application of the touchup compound. Cleaning will ensure good adherence of the compound to the unprotected metal substrate.
Hydraulic bending. For best results, use equipment designed to bend coated conduit. You can find hydraulic and electric benders with shoes sized for coated conduit. When bending coated conduit, use rubbing alcohol to clean the inside of the shoe and area of conduit you wish to bend.
Never use lubricant in the shoe or on the conduit. Lubricant allows the conduit to slip above the center line of the shoe, resulting in a flat elbow. A conventional shoe can remove 0.060 in. from the inside surface of a standard shoe, accommodating the same diameter conduit.
Hand bending. When using a conventional hand bender, use the next larger size bending shoe to allow space for the coating. You can make hand bends with a special coated bending hickey that reduces damage potential to the coating when making sharp bends, saddles, or offsets. Installers typically use these tools for conduit diameters ranging from half-inch. to 1 in.
Assembly. You should use special Z wrenches in lieu of standard adjustable pliers to assemble PVC-coated conduit and fittings. Z wrenches spread the clamping force and enable the tool to grip securely, without damaging the conduit coating. You can also use strap wrenches to tighten conduit or couplings without damaging the coating. For smaller conduit sizes, you can use Spin-It tools with air impact or standard ratchet wrenches to assemble the conduit and fittings faster than conventional methods. This method never touches the coating and saves time by eliminating the need to touchup damage marks.
Special sockets are available for use with ratchets to tighten encapsulated screws on conduit fittings, hangers, and clamps. Sleeves help seal corrosives from the threads at joints. Typically, you should not cut; however, you may need to remove portions of the sleeve when the fitting is close to others such as a close nipple. Here, you can cut away half of each sleeve and apply touchup compound to the threads and joints.
Certification and education. Several manufacturers now offer formal installer certification for end users and contractors who install coated conduit systems. Because manufacturers recognize the importance of proper installation, many offer free training for installers. Attending these seminars could help lead you to the best possible installation of a coated conduit system.
Dodds is an Engineering Consultant, Product Development, at ROBROY Industries, Verona, Pa.