Overload Protection
Circuit breakers do not blow like fuses. They are switches that automatically trip open to interrupt the flow of electrical current when it overloads the circuit. Power is distributed through your house through various electrical circuits that start in the main entrance panel. The 110-120-volt circuits have two conductors — one neutral (white) wire and one hot (black) wire. The 220-240-volt circuits may have two hot wires alone or a third, neutral wire may be added. In all cases, the hot lines are attached directly to the hot main buses. The neutral wire is always connected to the ground bus and never, under any circumstances, should it pass through a fuse or circuit breaker.
Fuses and circuit breakers are safety devices built into your electrical system. If there were no fuses or circuit breakers and you operated too many appliances on a single circuit, the cable carrying the power for that circuit would get extremely hot, short circuit, and possibly start a fire. To prevent electrical overloads, circuit breakers and fuses are designed to trip or blow, stopping the flow of current to the overloaded cable. For example, a 15-ampere circuit breaker should trip when the current through it exceeds 15 amperes. A 20-ampere fuse should blow when the current through it exceeds 20 amps. A fuse that blows or a circuit breaker that trips is not faulty. It has doing its job properly, indicating that there is trouble somewhere in the circuit. A blown fuse or tripped circuit breaker usually means there are too many appliances plugged into that circuit or some malfunctioning device, like an appliance with an internal short, is connected to the circuit. Locate and eliminate the cause of the trouble before replacing a blown fuse or resetting a tripped circuit breaker.
Caution: Never try to defeat this built-in safety system by replacing a fuse with one of a higher current-carrying capacity. The fuse or circuit breaker capacity should be equal to or less than the current-carrying capacity of the conductors. For example, don’t replace a 15-ampere fuse with a 25-ampere fuse. Replace fuses and breakers only with ones of the same size and amperage. You will cause certain damage to the device if you do that.
Circuit breakers do not blow like fuses; they are switches that automatically trip open to interrupt the flow of electrical current when it overloads the circuit. To reset a tripped breaker, turn it fully off and then back on.
Branch and Feeder Circuits
Circuits to all the devices in your home that require electrical power start from the fuses or circuit breakers. There are two types of circuits: feeder and branch. Feeder circuits use thicker cables that travel from the main entrance panel to smaller distribution panels called subpanels, or load centers. These auxiliary panels are located in remote parts of a house or in outbuildings, and they are used for redistribution of power, such as in a garage. Feeder circuits aren’t found in all houses.
Newer homes have three incoming power lines that supply 110-120/220-240 volts AC. This provides 110-120 volts for lighting, outlets, and small appliances and 220-240 volts for heavier appliances. All of the circuits in a home that run from either the main entrance panel or from other smaller panels to the various points of use are branch circuits. For 110-120-volt needs, a circuit branches out through a circuit breaker from one of the main buses and from the ground bus. For 220-240 volts, many circuits use only the two main buses. But all three wires are needed for devices that operate on both 110-120 volts and 220-240 volts.
The 110-120-volt branch circuits go through fuses or breakers, which are labeled either 15 or 20 amps. The 15-amp branches go to ceiling lamps and wall receptacles in rooms where less energy-demanding devices, such as table lamps, are found. The larger 20-amp circuits go to receptacles in the kitchen, dining, and laundry areas where heavy-duty appliances are used. A 15-amp circuit can handle a total of 1,800 watts, while a 20-amp circuit can handle a total of 2,400 watts, but these figures represent circuits that are fully loaded. In practice, you should limit the load on a 15-amp circuit to no more than 1,440 watts, and the load on a 20-amp line should exceed no more than 1,920 watts.
How can you know the load on a circuit? Add up the individual wattages for all lamps and appliances plugged into each circuit. When computing the load on each branch circuit, allow for motor-driven appliances that draw more current when the motor is just starting up than when it’s running. A refrigerator, for example, might draw up to 15 amps initially but will quickly settle down to around 4 amps. Suppose the refrigerator is plugged into a 20-amp branch circuit and a 1,000-watt electric toaster (which draws a little more than 8 amps) is also plugged into that circuit. If the refrigerator motor starts while the toaster is toasting, the total current load will exceed the current-carrying capacity of the circuit, and the fuse will blow or the circuit breaker will trip.
Keep reading to learn about proper safety practices when you’re working with your home electricity system.
Some home electrical repairs require a licensed electrician, but the repair or replacement of many electrical components can be done by a do-it-yourselfer. Make safety your first priority, and you’ll be amazed at what you can do to maintain and upgrade the electrical devices in your home.
Examine wiring regularly for safety reasons. Replace cords that have brittle or damaged insulation. All electrical devices and electrical wires are designed to provide the greatest measure of electrical safety, but you can defeat any built-in safeguards with carelessness and ignorance. To work safely with electricity, be aware of the following hazards and precautions:
- Never do anything that would break the conductor’s insulation. Do not, for example, staple an extension cord to a baseboard or wall. The staple can cut through the insulation and create a short circuit, which, in turn, can start a fire. Moreover, you should examine all wiring regularly and discard any cord with brittle insulation. Replace the old cord with a new one that has good insulation.
- Turn the power off before replacing a receptacle or a switch or doing any other work on a circuit. If your system operates with fuses, remove the fuse for the circuit you’re working on and slip it into your pocket or toolbox. If you leave it nearby, someone might put the fuse back in while you’re working on the circuit. If your home’s electrical system uses circuit breakers, trip the appropriate circuit breaker to its OFF position. Then, to make sure no one accidentally flips the circuit breaker back on while you’re working, put a piece of tape and a sign over the circuit breaker’s handle telling people what you’re doing.
- When you work on an electrical circuit, make all wire joints and connections inside an approved electrical box. There are several ways to join wires, but the best way is to use solderless connectors of either the crimp-on or screw-on wire nut kind. Never connect wires together in a behind-the-wall or in-the-ceiling location that is not accessible by simply opening an electrical box. In addition, when joining insulated wires to one another or when fastening them under terminal screws, make sure no uninsulated or bare wire extends beyond the connection. The insulation should go right up to the solderless connector or terminal screw.
- One of the best ways to join wires is to use solderless connectors called wire nuts. Twist the conductor ends together, and screw the wire nut into the twisted ends. Make sure no bare conductor is exposed.
- Everyone in the family should know where and how to throw the master switch that cuts off all electrical current.
- If there’s a chance of contact between water and electricity, do not wade in water until the master switch has been shut off.
- Always assume an electrical receptacle or apparatus is energized until you prove otherwise with a circuit tester or by pulling a fuse or tripping the disconnect plug.
- Use only insulated pliers when working with electricity.
- Stand on a dry board or wooden platform when working with a fuse box or circuit breaker box. Also, use a wooden rather than an aluminum stepladder to minimize the risk of shock when working with electrical wiring.
- You can save time by determining which electrical circuits activate which receptacles in your home and then diagramming or printing the information inside the circuit breaker or fuse box.