revolving wheel pipe cutter leaves a heavy inside ridge that is difficult to remove and may damage the passing through of conductors. Always ensure that you make a cut at right angles to the axis of the pipe (fig. 5-38).
Thin-wall conduit (EMT) and polyvinyl chloride (PVC) should be cut with a hacksaw because pipe cutters may flatten the end of the pipe. The pipe cutters also leave a ridge on the inside of the pipe that is hard to remove. There are tubing cutters made specifically for cutting EMT or PVC, but you need to be sure you have the right cutter for the job. When you are cutting conduit, use a vise to stabilize the conduit.
Flexible conduit and tubing should also be cut with a hacksaw. Because of its spiral construction, flex should be cut at an angle so that only one ribbon is cut all the way through. A slight reverse twist will separate the two ends (fig. 5-39).
Cutting any type of conduit leaves a sharp edge or burr on the inside of the pipe that must be removed by reaming. Reaming can be done with several tools. To ream rigid and intermediate conduit, you should use a pipe reamer. A rat-tailed file does a good job on any type of conduit. To ream EMT that has been cut with a hacksaw, you should use the heads of a pair of pliers, such as needle nose or side-cutting pliers, and they will do the job. The important thing is to remove any edges, or burrs, in the pipe that might cut the insulation when the conductors are pulled into the conduit.
The next step is cutting the thread on the end that was cut off. For the smaller pipe you use a ratchet type of die that turns directly with the handle. On larger pipe you use a die with a mechanical advantage; that is, you use a die that makes only a part of a revolution when the handle makes a complete revolution. Hand-held portable electric and shop type of threading machines are also available.
A conduit-threading die, like a plumber's die, makes a tapered thread, so that a coupling starts rather
Figure 5-39. - Cutting flexible conduit.
loosely but binds hard as it is set up. This tight connection serves two purposes: it makes a watertight joint and it makes a good electrical connection for a continuous ground throughout the length of the conduit.
Rigid polyvinyl chloride (PVC) conduit has been developed by many manufacturers. Some of the advantages of PVC conduit are the light handling weight, high corrosion resistance, ease of installation, leakproof joints, and easy wire pulling (because of the mirror-like walls). Refer to Article 347 of the NEC for installation requirements.
Permanent joints are made quickly in PVC conduit by cutting the conduit with a handsaw or hacksaw and removing the burrs with a pocketknife. When joining PVC conduit, always follow the manufacturers' instructions listed on the cement can for best results. A variety of threaded PVC fittings are available from manufacturers. Their use is covered in Article 370 of the NEC. The preferred method of installation is by the solvent-welding technique because the joints are waterproof and vapor-proof.
The NEC Article 346 through 348 applies to electrical conduits. It states that the "bends in conduits will be made so that the tubing will not be injured and that the internal diameter of the conduit will not be effectively reduced." In addition, the NEC has a table that indicates the minimum radius acceptable for various sizes of conduit. It also states that "a run of electrical conduit between outlet and outlet, between fitting and fitting, or between outlet and fitting, will not contain more than the equivalent of 4 quarter bends (360 degrees total) including those bends located immediately at the outlet or fitting."
When installing conduit, you will need to make bends to go over or around obstacles. Bends of various shapes will be needed, such as right-angle or 90-degree bends, offsets, and saddles. These bends must be made without reducing the inside diameter of the conduit in the bend. You will make most of these bends on the job as part of the installation procedure. They are called field bends. Factory-made bends may be used instead of field bends; however, they will cause you more cutting and threading, and they increase the cost of the job.
Most of the field bends will be done with manual benders or a hot box heater in the case of rigid nonmetallic conduit. Manual benders used to bend rigid conduit and EMT are of two types. These are the rigidContinue Reading