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Skilled Trades 1201

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.

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Skilled Trades 1201

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  1. Electrical Theory Skilled Trades 1201

  2. Basic Electrical Tools

  3. 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.

  4. 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.

  5. 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.

  6. 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?

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Types of Switching • Single Pole 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.

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