Cutting and Assembling Conduit
Codes sometimes require conduit, especially for exposed areas. Conduit has definite advantages: It protects the wires well, and the electrical system can be upgraded later simply by pulling new wires through the conduit. Conduit is the most difficult way to install wiring because it’s hard to bend. But it is still within the reach for do-it-yourselfers. For small jobs, use elbows and connectors at each turn to avoid bending conduit.
Codes allow many wires to be pulled through conduit. But the more wires you pull, the more crowded the conduit, so buy larger conduit than is required by code— say, 3/4-inch instead of 1/2-inch.
1. Measure the distance for the run - don’t forget to subtract for the connector or elbow you will be using. Cut with a tubing cutter by clamping it to the conduit and rotating it a few times. Tighten and rotate until the cut is made. Or cut with a hacksaw. Hold conduit against a cleat or use a miter box to keep it from rolling as you saw.
2. Ream the ends. Sharp edges can chew up wiring insulation in a hurry. Remove all burrs and rough spots from the inside of the conduit, using the reamer that’s attached to the tubing cutter or a file. File rough spots on the outside as well, so the conduit can slip easily into a connector.
3. Install a junction box. Where you have more than four turns to negotiate, install a junction box. When it’s time to pull the wires, it will let you start another run. More boxes and few bends ease wire-pulling.
Add an offset. Use an offset connector to keep the conduit flush against the wall when it’s attached to a box. The conduit can be bent to form an offset but adding an offset connector is easier.
4. Install pulling elbows. A pulling elbow makes negotiating corners easier. Remove the cover to pull the wires through. Don’t make any connections inside a pulling elbow; wires must pass through without a break.
For larger jobs, it is expensive and time-consuming to use connectors at each corner. Instead, bend the conduit. Bending isn’t difficult, but getting the bend in just the right location is tricky and requires some practice. Runs begin and end at places where you can get at wires to pull them. Codes generally forbid a total of more than 360 degrees of bends in a run. Add up the degrees of the bends you’ll be making in a single run before you start bending to ensure the total is less than 360 degrees.
1. Measure for a corner. To get conduit around a corner, first measure from the box to the top of the bend. Then subtract the bend distance and mark the conduit. (The bend distance for 1/2-inch conduit is 5 inches. For 3/4 - and 1-inch conduit, allow 6 and 8 inches, respectively.) Slip the conduit bender onto the tubing and align it as shown. After making the bend, trim section B by holding the bent conduit in place for measuring, and cutting the end so it just reaches the box.
2. Make the bend. With one foot on the rear of the bender, pull slowly and steadily on the handle. Be careful. Tugging too sharply will crimp the tubing and you’ll have to start over again with another piece. (Codes forbid installing crimped conduit.) Making crimp-free bends takes practice, so don’t be surprised if your first efforts fail.
3. To form an offset, start with a 15-degree bend...When mounting conduit on a flat surface, you’ll need to form an offset at each box. Offsets must be aligned with other bends in the tubing. A stripe painted along the length of the conduit helps you do this. First make a 15-degree bend. Roll the conduit over, move the bender a few inches farther from the end, and pull until the section beyond the first bend is parallel to the floor.
1. Use couplings to join sections. To join sections end to end, use either setscrew or compression couplings, securely fitted.
Caution! Make all connections mechanically strong. Pulling wires through conduit can put a strain on connections. Grounding depends on secure metal-to-metal connections.
2. Anchor the conduit. Anchor conduit runs with at least one strap every 8 feet and a strap within 3 feet of every box. For masonry walls, use screws and plastic anchors. When attaching to framing, simply drive barbed straps into the wood. To mount conduit inside walls, bore holes in the studs , or notch the framing and secure it with straps or metal plates every 8 feet.
3. Connect to boxes. The various types of box connectors differ mainly in the way they attach to conduit. Compression connectors grab the conduit as you tighten the nut with a wrench. To install a setscrew connector, slip it on and tighten the screw. Both types are available in 90-degree versions. All these connectors attach to the box with the same threaded stud and locknut arrangement used with cable connectors. Insert the stud into a knockout hole, turn the locknut finger tight, then tap the nut with a hammer and screwdriver to tighten it. A two-piece connector comes in handy when space is tight inside a box. Instead of a locknut, it has a compression fitting. As you tighten the nut, the fitting squeezes the conduit.
Pulling Wire Through Conduit
Now comes the moment when you realize why codes are so specific about bends, crimps, and burrs in conduit. Pulling wire can be surprisingly hard work. If you suspect that the wire is scraping against something that might damage the insulation, stop work, locate the trouble spot (you can find it easily by using the wire as a measuring device), and remove it. Purchase pulling grease, and lubricate the wires with it if you need to make a long pull.
1. Push through short runs. For short runs with only a couple of bends, you can probably just push the wires from one box to the other. Feed the wires carefully to protect the insulation.
2. Attach a fish tape. If you can’t push the wires, you’ll need a fish tape and an assistant. Snake the fish tape through the conduit, hook the wires to the fish tape and secure with electrician’s tape. Wrap the connection neatly so it can slide through the conduit.
3. Pull the wires through. As one worker feeds the wire in and makes sure there are no kinks, the other pulls. Pull the wires with steady pressure—avoid tugging. As the wires work past bends, expect to employ more muscle. If you have lots of wires or a long pull, lubricate the wires with pulling grease. Where possible, use gravity to aid the process. Feed the wires from above and pull from below.
4. Leave plenty of wire. Leave 6 to 8 inches of wire at each box. Never splice wire inside conduit—all wires must run continuously from box to box.
Running Wires Underground
If you want to install a lamppost in the front yard or install new power to the garage, run the wiring underground. Check local codes to see if you can simply run waterproof cable (labeled “UF”) underground or if you need to protect cable with conduit. Also find out how deep the wiring needs to be. The potential for shock is greater outdoors, so buy watertight fittings designed for outdoor use. Protect all exterior receptacles with ground-fault circuit interrupters. If you are installing only a light or two, you probably can extend power from an existing circuit. If the outdoor outlets will receive heavy use, you’ll need to establish a new circuit.
Caution! Before you start digging trenches, contact your utility companies to find out where all the underground pipes and cables are in your yard.
Tap an exterior receptacle... Add a weather-tight extension to an existing exterior receptacle, and run conduit from it. Attach it so the gasket will keep out moisture. Unprotected UF cable should exit from the conduit about 18 inches below grade through a special insulating bushing. Check to see if your local codes allow cable.
...or connect inside the house. If no exterior receptacle is handy, find a nearby junction box or run a new circuit from the service panel. At the point where the wiring leaves the house, install an LB fitting. Do not make connections inside the connector—wires must run from box to box.
Add a light to an existing switch. If you want a lawn light that will come on when you turn on an exterior light, tap into an existing fixture. Remove the fixture from its electrical box and install a weather-tight box extension into which you can run the wiring. Run conduit down the side of your house or hide cable inside the wall cavity.
1. To install a lamppost, first dig a post hole and trench. Various types of lampposts come with their own installation instructions. However, they all need to be firmly anchored to the ground. The simplest way to do this is to dig a deep post hole with a clamshell-type digger, set the post in it, and fill with concrete or tamped soil. If your trench must pass under a sidewalk or driveway, dig the trench on either side of the obstruction. Cut a piece of conduit about a foot longer than the span. Flatten one end to form a point. Drive the piece under and past the obstruction, cut off the flattened end, and connect it to conduit with couplings.
2. Plumb the post. After you run the wire and before you fill the hole, plumb and brace the post using scrap lumber. Attach the braces to the post with clamps and screw or nail them to the stakes. Add water to premixed concrete, shovel it into the hole, and trowel smooth.
3. Make the electrical connection. Wire the light using wire connectors. A light-sensing photocell accessory switches on the light at nightfall. If you also wire it to a conventional indoor switch, the switch can override the photocell when the light isn’t needed.
Digging Trenches - For short runs where the digging is easy, a shovel will suffice, although you’ll end up with a trench wider than needed. For large jobs, rent a walk-behind trencher, which makes a trench up to 2 feet deep. Give trees a wide berth to avoid damage to roots and time.