Simplest Ways for Understanding Wiring

Once you have ensured that you are working on only nonenergized wiring, then the installations are surprisingly easy to learn. Attaching boxes, routing cable, and installing lights and other fixtures often can be accomplished in short order. This article hits only the high points of electrical work. if you are at all unsure of how to install something correctly, hire a professional electrician.

The Service Panels

Understanding your electrical service begins with a look at the service panel. (You don’t have to remove your service panel cover, but you will need to if you install new circuits for new service.) Unless you have an old house with outdated equipment, three thick wires enter your panel. One “neutral” wire connects to a strip of metal called a neutral or hot bus bar. The two “hot” wires connect to the two hot bus bars, which run down each side of the panel; individual breakers are connected to the bus bars.

Each breaker is connected to a hot wire that sends power to an individual or “branch” circuit. A breaker is a safety device that turns itself off when there is an overload, short, or other problem with the wiring. To restore power, some breakers turn back on with a single flip; others must be flipped one way, then the other. Inside a service panel, you will find a mass of wires. Hot wires, which are black, red, or another color, attach to breakers and carry power to electrical outlets throughout the home. Neutral wires, which are almost always white, carry power back from the outlets to the panel, where they hook to a neutral bus bar. Bare copper or green ground wires also lead back from the outlets to the panel, where they attach to the same bar as the neutrals or to a separate grounding bus bar.

You’ll find a lot of wires in a service panel—hot, neutral, and ground. Be sure you know what each wire is before working in a panel.

If you have a fuse box instead of a panel with breakers, don’t panic. It may work fine, as long as you don’t have heavy electrical users. But if you will be adding service in your basement, you will need new electrical circuits. It’s probably time to hire an electrician to install a new breaker panel with at least 100 amps—200 is even better. When opening a service panel, be extra safety-conscious: Wear gym shoes or other rubber-soled footwear, and be sure to stay dry. And don’t touch any bare wires in the panel.

Safety Alert: If you suspect any problem with the wires that run to your house, or to your electrical meter, do not touch anything; call your electrical utility to come out and assess the situation.

Volts, Amps, and Watts

To put things as simply as possible, “volt” refers to the force with which power is pushed through wiring. Residential wires all carry between 115v and 125v, which is called 120v. Most devices and fixtures in a home use 120v, but some heavy users, such as air conditioners, electric stoves, or electric water heaters, use 240v. This amount of voltage is provided by two 120v wires.

Though voltage is the same throughout a house—120v per wire—the amount of power used varies quite a bit. This amount is measured in amperes or amps. A light fixture—especially an LED—uses a tiny amount of amperage, while a window air conditioner or refrigerator can use a lot.

Most 120v circuits have breakers and wires that can handle either 15 amps or 20 amps. A 15-amp circuit uses #14 wire, while a 20-amp circuit uses thicker #12 wire. (These are also called 14-gauge and 12-gauge wires, or 14 AWG and 12 AWG.) It is important that a #14 wire not be attached to a 20-amp circuit, or it can overheat dangerously before the breaker shuts off. Some very heavy 240v circuits use larger-amp breakers and correspondingly thicker wires. Thirty-amp circuits call for #10 wire, and 40-amp circuits require #8 wire.

Wattage (or “watts”) is a measurement of the power used by fixtures or devices. It is calculated by measuring volts times amps. So for instance, a 15-amp/120-volt circuit has a capacity of 1,800 watts. Codes require that it be loaded with no more than a “safe capacity” of 1,560 watts. And a 20-amp circuit should supply no more than 1,920 watts.

Circuit Wiring

Power passes from the hot bus bar to a breaker, and from there to a branch circuit via a hot wire. Each branch circuit supplies power to a number of outlets. Modern codes call for separate circuits (and separate breakers) for receptacles, for lights, for certain appliances, and so on. But in many homes, a single circuit may supply some receptacles, some lights, and maybe even an appliance as well.

In homes with well-organized circuitry, it is fairly easy to determine which users are controlled by which circuit: It may be a group of receptacles or lights, or it may be a certain room. However, don’t be surprised if your circuits go all over the place and if a single circuit controls receptacles in one room, lights in another, and so on.

Contemporary electrical codes call for many more circuits than used to be required. For instance, in a kitchen, you may need two circuits for countertop receptacles, as well as dedicated circuits for the refrigerator, the microwave, and an exhaust fan. And a bathroom’s receptacle may need to be on its own circuit. A duplex receptacle—the most common type, with two outlets— may be “split,” so that the outlets are on separate circuits.

Avoiding Overloads

When adding new service in a basement, you may be able to extend an existing electrical circuit, but only if it has enough “room” for new users. If you add too much in the way of electrical users, you can overload the circuit, and the breaker will trip regularly. To determine if you can piggyback onto an existing circuit, add up the wattage or amps of the light bulbs, the plugged-in appliances, and the fixtures already being used, and add in the users that you plan to add. The result should be less than the “safe capacity” for the circuit.

For a 15-amp circuit, safe capacity is 12 amps or 1,440w. For a 20-amp circuit, safe capacity is 16 amps or 2,400w. If users will be over the safe capacity, then you need to install a new circuit. Check that your service panel has empty spaces where you can install new breakers; if not, you may need to hire an electrician to install a new panel.

Do You Need a New Service Panel?

Determining whether you need a new, larger service panel calls for some complicated calculations, which I cannot get into here. I can say this: If you have a 100-amp service panel, and the amperage of all your breakers adds up to more than 160 amps, you should consult with an electrician or your building department to see if you need a new 200-amp panel.

Common Codes

Electrical codes are constantly changing, usually in the direction of greater stringency. Here are some of the more common ones that you should be aware of. The following are based on the latest National Electrical Code® (NEC) regulations, but be sure to check with your local building department to be certain you comply with their regulations.

  • The service panel must have enough amperage. A 100-amp panel is usually sufficient for a medium-sized home, but a 200-amp panel is preferred. Circuits should be labeled on the panel.
  • Wire sizes must match the breakers: 14-gauge for a 15-amp breaker, and 12-gauge for a 20-amp breaker, for instance.
  • Nonmetallic (NM) cable is allowed in most areas, but conduit or metal-clad cable is required in other locales. Where wiring is exposed rather than hidden in walls, it should run through conduit.
  • The cable should be run in areas where drywall screws cannot reach it or should be protected with metal nailing plates.
  • There are specific rules for running NM cable. You may need to staple it within 8 in. or 12 in. of a box, depending on whether the box has a cable clamp.
  • Electrical boxes must be within 1⁄8 in. of flush with the surrounding drywall, tile, or other finished surfaces.
  • Inside a box, there should be at least 6 in. of unsheathed wire. All splices must be made with wire nuts, not tape.
  • Only one wire can be connected to a single terminal on a device or fixture.
  • You may be required to wrap switches and receptacles with electrician’s tape to protect wires and terminals.
  • Install GFCI receptacles wherever the area may get damp.
  • In most cases, there should be separate circuits for lights and receptacles.
  • In a bathroom, there should be an exhaust fan. You may or may not be allowed to put a fan/light on the same circuit as a receptacle.
  • Install at least one receptacle every 12 ft., and at least one receptacle on every wall that is at least 6 ft. long.

Wiring Supplies And Tools

In most areas, NM cable is allowed with either metal or plastic boxes. The supplies and tools shown here should handle most common wiring situations in a basement. If you live in an area where the conduit is required.

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