Jeff's DIY

Advice on doing your own diagnosis and repair

Advice from the book Can I Do It Myself?

Home Electrical Basics and Circuit Installation

Almost all American homes are served with 220 Volt AC of at least 100 amps. Voltage refers to the strength of the power and amps refers to the total current available to your breaker box. AC refers to the type of current-in this case "alternating" versus "direct." Most, if not all, home appliances accept alternating current of either 110 or 220 volts. Many electronics, such as computers, use direct current, but they have their own power supply that converts your home outlet AC power to the various DC voltages needed by the device. The outlets in your home are designed to be fool proof. A 110 volt outlet will not accept the plug of an appliance that uses 220 volts, and vice versa. There are also several types of 220 volt outlets that are designed for different appliances, depending on the power needed for that type of appliance. Primarily, an electric oven will use higher power levels and has a 6-gauge outlet; whereas an electric dryer can run on a 10-gauge outlet. You wouldn't want to plug your oven into a dryer outlet, but the electrician will make sure you can't. So, if you're going to be your electrician or your friend's electrician, you have to understand power requirements of typical appliances and the associated wire gauges and outlets required by the electrical codes.

Let's talk about the electrical service and the breaker box. You can take the cover off the box if you want to look while reading, but do not touch anything inside. You will see the 2 main lines, usually coming in the top and attaching to the gridwork on the back of the box after passing thru the main breaker. Each of these wires brings 110 VAC, but the two voltages are out of phase. When one wire reaches peak voltage, the other reaches its low. A third wire brings in the return or ground wire, which attaches to ground bars along the sides of the box. The ground may travel back to the main service line or just to a post driven deep into the soil outside your house. The gridwork in the back of the box (behind the breakers) is designed so that alternating breakers as you go down the box receive power from one and then the other main line. This is so that any 2 breakers next to each other can provide a total of 220 volts. The wiring for a 220 volt appliance, such as an electric oven or A/C system, will use a double breaker. Always use a double breaker for wiring a 220 volt outlet or appliance. Breakers almost always have a pivot point and a clamp to grab the grid. Usually the pivot point is on the outside, and the clamp slips over a protrusion near the center of the box. Your wires then slip under the screw on the outer edge of the breaker. The grid is hot whenever the main breaker is on, so be careful in there. The main lines coming into the box above the main breaker are always hot when your power company is delivering power.

Now let's talk wire. The breakers are sized to protect the wiring in your house. The breaker size must be low enough for the gauge wire it is protecting; and that includes all of the wire along that circuit (it does no good to use a large gauge at the box if you switch to a smaller gauge farther along in the wall). A 110 volt outlet can take from 10 to 20 amps. Here is a list you can use (notice that higher gauges correspond to less current/smaller diameter wires):

Wire Use; Rated Ampacity; Wire Gauge

Low-voltage Lighting and Lamp Cords; 10 Amps; 18 Gauge

Extension Cords; 13 Amps; 16 Gauge

Light Fixtures, Lamps; Lighting Runs; 15 Amps, 14 Gauge

Receptacles, 110-volt Air Conditioners, Sump Pumps, Kitchen Appliances; 20 Amps; 12 Gauge

Electric Clothes Dryers, 220-volt Window Air Conditioners, Built-in Ovens, Electric Water Heaters; 30 Amps; 10 Gauge

Cook Tops; 45 Amps; 8 Gauge

Electric Furnaces, Large Electric Heaters; 60 Amps; 6 Gauge

Electric Furnaces, Large Electric Water Heaters, Sub Panels; 80 Amps; 4 Gauge

Service Panels, Sub Panels; 100 Amps; 2 Gauge

Service Entrance; 150 Amps; 1/0 Gauge

Service Entrance; 200 Amps; 2/0 Gauge


The 110 volt wires that attach to individual breakers will be 12 or 14 gauge. Most 12 gauge wire has a yellow outer cover. Some 12 gauge wire may have 4 conductors, but a standard 110 volt outlet only accepts 3 wires. The 4-conductor wire would be used for specialized circuits or outlets. 14 gauge wire is the standard minimum diameter for most outlets. Make sure you use a 20 amp outlet if you want to use all of the power available from a 12 gauge wire. Though 20 amp appliances are rare, you would burn up a 15 amp outlet using a 20 amp appliance/power tool. Often, a 12 gauge wire will be used to supply a set of kitchen outlets or similar arrangement. The 12 gauge wire will originate at a 20 amp breaker and go straight to a GFCI outlet in the kitchen. You may even have two or more such circuits for a large kitchen. The rest of the outlets will then be wired to the "load" terminals of the GFCI outlet using more 12 gauge wire. The GFCI will trip if it detects an alternate current path (such as your body). GFCI is also required for bathroom outlets and outdoor outlets.

Let's talk about fool-proof wiring. The codes have been designed to keep you out of trouble in the home, but you must follow them to keep the fools at bay. Every modern circuit includes a green or bare ground wire. For a 110 volt outlet, the ground wire attaches to the frame of the outlet and the round prong of your appliance. The white wire is the return wire attached to the silver color terminals of the outlet and the larger flat prong of the appliance. The black (hot) wire attaches to the gold or brass colored terminal and the smaller prong of your appliance. Both the white and ground wires attach to the ground strap in the breaker box, but they serve different purposes. The white wire carries current back from the appliance. The ground wire's only purpose is to ground the appliance frame. This is a safety feature such that if the hot wire accidentally touches the frame, the ground wire will provide a return path to trip the circuit breaker rather than allowing the appliance frame to become a source for electrocution. Many smaller appliances do not have a metal frame and therefore may not use the ground wire (or third prong).

Now 220 volt wiring is totally different. There are two hot wires-black and red. Also, some modern appliances (such as ovens) use both 110 and 220 volt service through one outlet. Modern codes require 4-conductor 6 gauge wire for electric ovens. This wire will have a red and black wire for the hot leads that run the heating elements. There will be a white ground wire to return 110 volt current from either of the red or black wires that serves the 110 volt circuits that run the lights and controls of the oven. The green or bare wire will again be used to ground the frame. Always read the instructions carefully when wiring a 220 volt outlet or appliance, because what I'm telling you is common code but not always followed. I have seen some pretty crazy things done over my years of rewiring things, and some that are quite dangerous.

Let's talk a little about wall switches. A simple single pole switch will just connect its two terminals when turned on. Just connect the hot lead to one terminal and the load (usually the circuit for permanent lighting or maybe a ceiling fan) to the other. The white return wire is connected directly to the load, but the ground wire should connect to both the load frame and the switch ground screw. If you want two or more switches to operate the light, you will need 3-pole switches and a lot more wire. Three-pole switches connect one terminal to the second or third terminal, depending on the switch position. The way this works is the hot power is supplied to the input/output terminal of one switch, and the load is attached to the input/output terminal of other switch. The white return and ground can be passed across and then sent directly to the light from the second switch. Another pair of conductors (usually a standard three-wire of which only the insulated conductors are used) must run between the two switches, attaching to the other terminals. If you are sure to attach the hot input to the input terminal of the first switch and the load to the same terminal of the second switch, it will not matter which terminals the other wire attaches to. When the first switch is in either position, it will make one of the two middle wires hot. The second switch will then connect either center wire to the load.

For circuit installation, set your wire coil down where you intend to pull from as you run the route. This may be at the outlet/switch or the breaker box. Prepare the route by cutting any holes you will need to route behind walls and/or mounting any conduit. Holes are best cut in the plate at the top of the wall versus in the studs. Going thru the studs is OK to save wire as long as the holes are centered in the stud.

Electrical boxes are usually required at the business end by any code I have read, even for direct connections. Boxes come in various sizes for different purposes, and they have separate boxes for new construction and adding to existing drywall. New work boxes are nailed to a stud or joist with 1/2 inch sticking out to come even with 1/2 in drywall. Old work boxes are installed by carefully cutting a hole in the drywall near a stud, inserting the box, and tightening the screws until the clamps in back are tight against the back of the drywall. A heavy ceiling application, such as a fan or large chandelier, requires a special box that ties into the roof trusses.

Conduit is only required if the plastically-insulated wire would otherwise be exposed to someone that could penetrate it with a sharp tool. Likewise, clamps at the outlet box are not needed inside walls, as long as the box is made of plastic. Clamps that attach to a box or conduit are needed whenever the wire insulation could be cut by a metal edge. You always need a clamp to hold the wire where it enters the breaker box. There may be room to add a wire to an existing clamp--otherwise, take out a plug and install a new clamp. Route the wire to the outlet/switch by pulling it along the route. Pass it into the outlet/switch box leaving about three or four inches for attaching. Strip the insulation about a half inch. Connect wires to wires using wire nuts of the correct size (usually indicated on the packaging). To connect wires to screws, curl the wire 180 degrees, slip around the screw such that the end is clockwise from the rest and the wire extends away perpendicular from the body of the outlet or switch, and tighten the screw firmly.

Shut off the main breaker or be very careful working inside the breaker box. Pass the wire through the clamp far enough to reach the breaker plus the distance from the side wall of the box to the breaker. Clamp it off and remove the outer insulation of the wire. Install the correctly-sized breaker for the wire you are using. Strip the wire ends about a half inch using a wire stripper. Route the wires along the side of the box down to the breaker for the black/red wire and to the spot where the common and ground wires will go into the grounding strip and make a right angle so the wires come straight in. Make sure the breaker is off, loosen the breaker screw enough to pass the stripped black or red wire into the breaker and tighten the screw firmly. Similarly, attach the common and ground wires to the ground bar. You can now close the breaker box cover.

Move to the other end of the wire again, pass it through the back of the box out the front, stripping the wires and attach to the switch/outlet. Carefully bend and push the wires into the box and attach the switch/outlet to the box. Make sure any bare ground wire does not extend out near the hot terminals and cover the box. Staple the wire within a foot of the box and along the route as necessary to keep it out of range of any drywall screws or picture hangers that may come into the wall later. Use large staples or wire clamps to avoid piercing the insulation. If you have completed the circuit to the load, you can now turn the breaker on. Voila, you have a new circuit.

One caution if you want to extend an existing circuit to a new box-never use a reduced wire size when extending a circuit. The reason is, the new circuit could melt the wire before the circuit breaker trips.

Low Voltage Wiring

Low voltage is used wherever high voltage is unnecessary. Common examples include telephone, TV, Ethernet, intercoms, audio speakers, and closed circuit cameras. These circuits are not dangerous, but you need to understand them to work on them. Most important in these applications is to preserve the signal strength as load is added. What I mean is, you cannot add an unlimited number of devices to these circuits unless you boost the signal. Telephone lines are not too sensitive to signal level, but cable TV is. Also, you cannot add an Ethernet outlet unless you have a router with an open port to plug it into.

If you have a hardline phone, it's relatively easy to add an outlet. Telephone wire usually comes in four-conductor cable, but only two wires are used in a single-line phone-usually green and red. You can connect the new outlet to another outlet or to the phone box inside the house.

To add a coaxial cable TV outlet, look in your cable box inside the house. If there is an extra port on the existing terminal block, you can probably use that by removing the plug, connecting your new wire, and routing it to your new outlet. If there is no spare port, you can split the signal on an existing wire by removing the least critical wire from the terminal block and adding a "Y" adapter to that port to allow two wires to be connected. Never split the port that is serving your internet service, as the signal level there has a tight tolerance. If the signal to either split TV wires degrades such that your reception is poor, you can buy boosted "Y" adapters for this purpose. These require power. If you do not have power near the cable box, you can buy boosters that attach at the outlet end of the wire.

If you are adding speakers to an audio system, please read my tip on this subject in the automotive electrical section. You cannot split the speaker signal at the back of your stereo amplifier nor attach a new speaker unless the total resistance seen by the amp is above that specified by the amp manufacturer, or you may damage the amp.

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