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Wednesday, 11/19/2008

Electrical Basics

Plumbing and electrical systems may seem very different, but there are significant parallels. Water flows through a pipe under pressure and at a certain rate - gallons per minute. Electricity flows through wires, also under pressure called voltage. When you turn on a device, electricity flows at a rate measured in amperes, abbreviated as amps. The product of volts and amps (volts x amps) = watts. Since electrical consumption in a building is relatively high, the unit of measure most often used is the kilowatt, which is equal to 1,000 watts. The total amount of electrical energy used in any period is measured in terms of kilowatt-hours (kwh).

Electrical Overload Protection

Electrical power is distributed through your home on circuits that start in the main entrance panel. The 120 volt circuits have two conductors, one neutral (white) wire and one hot (black) wire. The 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 by circuit breakers or fuses. The neutral wire is always connected to the ground bus and should never pass through a fuse or circuit breaker. A bare ground wire is also included and attached to the grounding point at the outlet, and the ground bus in the circuit breaker panel. In the 240 volt circuit, each hot wire must be connected to a different hot bus in the panel. Breakers for 240 volt circuits are designed to do this for you.

Electrical fuses and circuit breakers are safety devices that protect both you and your power system. They shut down a circuit when the amperage flow is too high. Without this protection, a circuit could overheat and become a fire hazard. A fuse that blows or a circuit breaker that trips indicates a problem somewhere on that circuit. There could be too many devices plugged in, something is consuming more than the circuit can safely carry, or there is a defective device. Locate and eliminate the cause of the trouble before replacing a blown fuse or resetting a tripped circuit breaker. Never, under any circumstance, try to defeat this safety system. For example, never replace a 15 amp fuse with one of a higher rating. Fuses and circuit breakers are designed to protect wiring of a certain size, known as gauge. Installing an oversized fuse or breaker could allow the wire to overheat and become a fire hazard. If you can't find the reason fuses or breakers keep tripping, call a licensed electrician for assistance. And be very careful - a defective device with a short circuit could injure or kill you.

How can you know the load on a circuit in amps? Add up the individual wattages for all devices on that circuit and divide by the volts. For example, if there are 2 lamps plugged in and each is rated at 75 watts, the total amps would be 75 x 2 / 120, or 1.25 amps. Be sure to allow for motor-driven appliances that draw more current when the motor is just starting up than when it's running. A refrigerator 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 circuit and a 1,000 watt electric toaster is also plugged into that circuit. If the refrigerator motor starts while the toaster is being used, the total current load will exceed the capacity of the circuit and the fuse will blow or the circuit breaker will trip. In this example, the total load would be 1000 / 120 = 8.33 amps, + 15 amps for refrigerator startup = 23.33 amps. This circuit should probably be upgraded to 30 amps (circuit breaker AND larger wiring), or plug one of the devices into a separate circuit.