Electrical Theory Skilled Trades 1201

Basic Electrical Tools

Overloads Overload : an overload occurs when the appliances and lights on a circuit require the amount of current on the line to be more than can be safely handled by the circuit. When this happens a breaker will “trip” or a fuse will burn in two breaking the circuit.

Shorts A short circuit occurs whenever a conductive part of the circuit touches another current- carrying wire or touches something that is grounded. The rate of current flow quickly becomes excessive, producing heat, which causes a breaker to trip or fuse to blow. Shorts or overloads can cause fires if the circuit does not have a fuse or has the wrong size breaker.

Determining Wattage A common household has both 120 volt and 240 volt current. Wattage is the power available in a circuit. To determine wattage, determine the amperage (amp rating) by examing the circuit breaker or fuse. 15-20 amps for most room circuits, 30 -50 amps for heavy duty circuits. Watts = volts x amps Ex. A 15 amp circuit with 120 volts can carry (15 x20 =) 1800 watts. It is important to know wattage so that circuits do not become overloaded.

Use the table on the next slide to help answer the following questions: How many watts are required in a kitchen that has a blender, coffee maker, microwave and refrigerator? Why do clothes dryers and ranges always have their own circuit? What would happen if a heater(portable) and clothes iron were plugged into a circuit that has 120 volts and a 15 amp breaker?

Wire Basics There are three types of wires: Copper Copper clad aluminum Aluminum You always use the type of wire that is already used in your home.

Wire Size Wire size is measured by gauge. The bigger the gauge the smaller the wire. Most often residential wiring uses 12 or 14 gauge wire in a sheathed cable.

Estimating Wire Needs To estimate the amount of wire needed follow these steps: Measure the distance between the outlet and power source. Add an extra foot for every connection you will make. Add 20% for a margin of error.

Twist on Wire Connectors You will be connecting wires using twist on wire connectors. To connect wires: Wires must be spliced, ie. Twisted around each other. Insert the wires into the connector with a slight twisting motion. The wire connector should completely cover the splice and a little of the wire insulation. Wrap the connector and an inch of wire with electrical tape for extra safety.

Types of Switching Single Pole Switches Three Way Switches A switch with two terminals. It is the only control on a circuit. Three Way Switches A switch with three terminal screws. These are used to control a circuit from two places, for example turn on/off a light from two ends of a hallway. Double Pole Switches Has four terminals. Normally used to control 240-volt appliances.