PVC conduit and fittings are extremely popular, both because they are inexpensive and easy to cut, but also because making the connections is very easy using PVC solvent cement. A properly done cemented joint is permanent and both airtight and watertight, and it takes less than a minute.
PVC Conduit and Fittings
Like PVC plumbing pipe, rigid PVC electrical conduit comes with a variety of union, transition, and bend fittings that make it easy to join lengths of conduit together and connect the conduit to electrical boxes, junction boxes, and other PVC components. Rigid PVC electrical conduit is known as "schedule 40 PVC conduit." It comes in 10-foot lengths and in diameters of 1/2-inch, 3/4-inch, 1-inch, 1 1/4-inch, 1 1/2 -nch, and 20inch. The lengths of conduit have one smooth and and one hubbed end. When joining lengths of conduit, you simply solvent-glue the smooth end of one piece into the hubbed socket of another piece. Lengths of conduit can be cut with any saw, but the best way to cut PVC conduit is with a PVC tubing cutter, of the same type used to cut PVC plumbing pipe.
The "glue" used to join rigid PVC conduit and fittings is officially called PVC solvent cement. It comes in a small metal can with a twist-off cap, and is the same material used to join PVC plastic plumbing pipes and fittings. The cap includes an applicator sponge attached to a wire stem. A small can of cement has an applicator pad suitable for conduit up to about 3 inches in diameter. For conduit larger than 3 inches (very rare in residential use), it's better to use a large can, which has a larger applicator pad.
There are several types of solvent cement available for different types of plastic, so make sure to buy a product that is designed for PVC. There are also "universal" solvent cements available that claim to be suitable for all types of plastics. Avoid these, and buy one that is intended for use with PVC pipe only.
Is Primer Necessary?
When gluing PVC plumbing pipe, plumbers typically use a primer before applying the PVC cement. Primer cleans and dulls the surface of the pipe to promote bonding. It's fine to use primer with PVC electrical conduit, but many electricians skip this step unless it is required or recommended by the conduit manufacturer or by the local building authority.
Tools and Supplies You Will Need
Conduit that is installed outdoors is subject to expansion and contraction as temperatures rise and fall, and this expansion can place stress on joints. For this reason, special expansion couplings are used when conduit is installed outdoors. These couplings are glued on both ends into the conduit run, but have a sliding, flexible middle joint that expands and contracts as the temperature changes.
Measure Conduit Pieces
Plan out the conduit run with the necessary bends, transitions, and electrical boxes. All electrical boxes and junction boxes should be secured in place to walls and framing member before you cut conduit pieces. When measuring conduit lengths, make sure to accommodate the overlap where the end of one piece will slide into the socket of another piece.
Cut the Conduit
Use a PVC tubing cutter or hacksaw to cut the straight lengths of conduit to the desired lengths. Deburr the cut ends of the conduit, using a utility knife or emery cloth. This removes any small fibers that may have been left when the conduit was cut.
Wipe the outside of the conduit and inside of the fitting with a rag to be sure they are clean.
Test-Fit the Layout
Before gluing up the conduit lengths, it's a good idea to test-fit the pieces to make sure the layout works. Make sure all electrical boxes are solidly anchored before you do this, and that any threaded conduit connectors are attached to the boxes.
Assemble the entire layout, including whatever transitions or union fittings are required. Once the pieces are dry-fit in exactly the position you want them, draw a straight line running across both the conduit and the fitting at each joint, using an indelible marker. These "registration" marks will make it easy to quickly align the pieces as you permanently glue the joints together. This is especially helpful on complicated runs of conduit, where there are many bends and offsets.
Glue the Joints
Disassemble the pieces and lay them out on the floor in the same configuration. Starting at one end of the conduit run, apply an even coating of PVC primer (if you are using it) to the inside and outside of the first connection. Make sure to coat the entire surface of both pieces.
The primer will dry almost instantly. As soon as it does, apply a thin but complete coat of PVC solvent glue to both surfaces. Insert the conduit into the fitting and push until the conduit bottoms out in the fitting socket. While continuing to apply pressure, turn the pieces, giving them a 1/4-turn twist. This distributes the solvent glue and ensure the joint is fully covered. If you have made registration marks on the conduit, make sure to align these marks as you twist the conduit.
Hold the pieces together for 30 seconds (or for the length of time recommended by the solvent glue manufacturer) until the glue is fully hardened. If there is excess glue around the joints, you can wipe it away with a rag while is it is still wet.
Work joint by joint along the conduit run until the entire layout is complete.
Finish the Installation
When all joints are glued, attach whatever conduit clamps are necessary to secure the conduit to the walls or framing members. For standard 1/2-inch to 1-inch diameter conduit, it should be anchored to walls or framing members every 3 feet, including within 3 feet of all electrical boxes.
The conduit is now ready to fish electrical conductors through it.