Before making electrical connections, you’ll need to remove some of the sheathing that encases the three or four wires of the cable and strip some of the insulation that coats the individual wires. Stripping techniques are simple, but exercise care when removing sheathing in order to avoid damaging any of the underlying insulation. Also be careful to strip the insulation without nicking the copper wire— this would weaken it. Strip wires before inserting them into the box. That way, if you make a mistake, you can cut off the damaged portion and try again.
1. Slit the sheathing. The easiest way to remove plastic sheathing from nonmetallic sheathed cable is to use an inexpensive cable ripper. Slip 6 to 8 inches of cable into the ripper’s jaws, squeeze, and pull. This slits open the sheathing without damaging the insulation of internal wires. The same job can be done with a knife, but you must be careful: Run the blade right down the middle so it doesn’t strip insulation from the wires.
2. Peel back the sheathing. Pull back the sheathing you have just slit, as well as the paper wrapping or strips of thin plastic, if any. You’ll find two or three separately insulated wires, as well as a bare ground wire.
3. Cut away the sheathing. Cut off the sheathing and paper. Remove the slit sheathing with a pair of side cutters. Or use a utility knife, taking care to point the blade away from the wires.
Caution! - This job is simple but it must be done with great care or you could end up with dangerous electrical shorts. If you think you may have accidentally damaged some insulation, cut the cable back to a place behind the potentially dangerous spot and start again. Another possible problem: If you cut into the copper wire while stripping the insulation, you can weaken the wire so that it is liable to break while you are making a connection later.
4. Strip the wire. To strip insulation from wires, use a combination tool, which has separate holes for the different sizes of wires. Locate the wire in the correct hole, clamp down, give it a twist, and pull the tool away from you. With an adjustable stripper, set it for the wire size, twist, then pull the tool away from you. Stripping also can be done with a utility knife, but be careful not to dig into the copper wire. Place the wire on a scrap piece of wood, hold the blade at a slight angle, and strip the insulation by slicing off thin strips until you reach wire.
Joining solid wires - Join solid wires by using a pair of lineman’s pliers. Cross the two wires, grab both wires with the pliers, and twist clockwise. Both wires should twist—-do not just twist one wire around the other. Twist for several revolutions, but don’t twist so tightly that the wires are in danger of breaking. Screw a wire connector onto the two wires.
1. Joining stranded to solid wires - Often a stranded wire (made of many thin wires) has to be spliced to a solid wire, as when hooking up a light fixture or dimmer switch. Because the stranded wire is more flexible, the two won’t twist together. Wrap the stranded wire around the solid wire.
2. Fold the solid wire over. Bend the solid wire so it clamps down on the stranded wire. Screw a wire connector onto the two wires, and wrap the connection with electrician’s tape.
Working with Wire
The final—and most gratifying— phase of an electrical installation comes when you tie all those wires together and attach them to the switches, light fixtures, and receptacles. Don’t take shortcuts with wire connections and splices. Cap splices with wire connectors rather than only tape, and wrap tape around each connector. Make pigtails wherever they are needed instead of trying to connect two or more wires to a terminal. Finally, don’t overcrowd a box with too many wires.
Using wire connectors - To complete a splice of two or more wires, use wire connectors. These come in a variety of sizes. Select the size you need depending on how many wires you will connect as well as the thickness of the wires (see chart, left). Wire connectors firm up the splice and protect bare wires better than tape. First twist the wires firmly together. Do not depend on the connector to do the joining. Twist the wire connector on, turning it by hand until it tightens firmly. As a final precaution, wrap the connector clockwise with electrical tape, overlapping the wires.
1. To connect a wire to a terminal, form a loop. Strip just enough wire to wrap around the terminal—about 3/4 inch. Then form it into a loop using needle-nose or lineman’s pliers. It takes practice to make loops that lie flat and are neither too big nor too small.
2. Fasten to the terminal. Hook the wire clockwise around the terminal so that tightening the screw will close the loop. With receptacles, the black wires go to the brass side, white to silver. Tighten firmly, but avoid over tightening, which can damage the device. If you do crack a device in any way, throw it out.
3. Solder a splice. A few codes require that splices be soldered. More often, soldering house wiring is prohibited. If you need to solder a splice, start by twisting the wires together. Heat the wires with a soldering iron, then touch lead-free, rosin-core solder to the splice. The solder should melt into the splice.
Add a pigtail where two or more wires attach to a terminal... Never attach more than one wire to a terminal. Codes prohibit it, and it’s unsafe because terminal screws are made to hold only one wire. An easier way to join many wires to a terminal is to cut a short piece of wire (about 4 inches), strip both ends, and splice it to the other wires as shown to form a pigtail.
...or make a soldered splice. Twist wires together so that one extends 1 inch beyond the splice. Solder the twist and loop the extended wire. Tape the soldered splice before screwing the wire to the terminal.
Caution! Make sure local codes permit soldering. Most receptacles and switches have connection holes in the back. To make a connection, strip the wire (a stripping gauge often is provided, showing you how much insulation to remove) and poke it into the correct hole. On a receptacle the holes are marked for white and black wires. However most professionals do not use these holes. Wires inserted this way are simply not as secure as those screwed to a terminal.
Grounding receptacles and switches - How you ground devices like receptacles and switches depends on the type of wiring you’re using as well as the type of box. With flexible armored cable (BX), Greenfield, or rigid conduit, the metal of the wiring casing and the metal of the box substitutes for the grounding wire. Simply by attaching the device firmly to the box, you have grounded it. Some local codes require that you also attach a short grounding wire, as shown. If you’re working with nonmetallic sheathed cable (Romex) and metal boxes, connect short grounding wires to the box and to the device. With nonmetallic boxes, the cable’s grounding wire connects directly to the device.
Replacing Plugs and Cords
Faulty plugs pose the most common shock and fire hazards in the house. Plugs get stepped on, bumped against, and yanked out by their cords. It’s a good idea to regularly inspect your plugs, especially if you have some old ones, for loose connections, damaged wire insulation, and prongs that have been bent so often they are in danger of breaking. Fortunately, it is easy to replace faulty plugs to make your home significantly safer.
Types of plugs - Round-cord plugs often accommodate fairly thick wire and are used for moderately heavy appliances such as irons. Flat-cord plugs are suitable for lamps, radios, and other low-amperage devices. Newer lamp and extension cord plugs are polarized, with one blade wider than the other. Standard grounded plugs have a third, round prong for grounding; the two flat prongs are polarized. Appliances that use 240 volts require heavy-duty three-pronged plugs of various configurations. The one shown here is for a 30-amp, 240-volt dryer.
Types of cords - For flexibility, cord wires are stranded, not solid. Zip cord, so called because the two wires can be easily zipped apart, is for light duty. Use cords with 16-gauge wire for appliances pulling 15 amps or less and 12-gauge wire for 20 amps or less. For 240-volt appliances, use wire that is 10-gauge or thicker.
1. To replace a round-cord plug, strip and insert the cord. Snip off the old plug. Remove the cardboard cover from the new plug, and slide the snipped-off end of the cord through. Strip off 3 inches of outer insulation and about 1/2 inch of wire insulation.
2. Tie Underwriters knot. This special knot will ensure that tugging the cord won’t loosen any electrical connections. Make the knot close to the end of the stripped outer insulation.
3. Bend hooks. Twist the wire strands tight. With a pair of needle-nose pliers, shape clockwise hooks to wrap around the screw shafts.
4. Connect the wires. Hook the wires on the screw shafts (attach the black wire to the brass-colored screw), and tighten. Tuck in stray strands.
5. Replace the cover. Check to be sure all wires and strands are neatly inside the plug. Slip on the cardboard cover.
Don't Change the Plug to Fit the Receptacle:
- If your appliance or tool has a plug with a third, round prong, then it should only be plugged into 3-hole outlets that are properly grounded. If you remove the grounding prong, or if you use a plug adapter that is not connected to a ground, you will disable a feature designed to protect against electrical shock.
- Some appliances and tools are “double insulated” and do not need the extra protection of a grounding prong. You can plug them into an ungrounded outlet and still be protected from shock.
1 .To repair a 240-volt plug, slide the plug onto the cord. A 240-volt plug has a steel clamp that grips the cord, so you don’t have to tie an Underwriters knot. Slide the plug onto the cord and strip about 1/2 inch of insulation from the ends of the three wires. Twist the strands tight, and use needle-nose pliers to form hooks.
2. Attach the wires. Attach the black and red wires to brass-colored terminals, and the green one to the silver-colored terminal. Tuck in any loose strands as you tighten the terminal screws. Tuck all the wires in place, tighten the cord clamp, and slip on the cardboard cover.