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Electrical Principles and Wiring Materials

Electrical Principles and Wiring Materials. JTE2023 ELECTRICAL & ELECTRONIC TECHNOLOGY. +. Duracell. Direct Current DC. a circuit containing a battery is a DC circuit in a DC circuit the current always flows in the same direction. Alternating Current (AC).

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Electrical Principles and Wiring Materials

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  1. Electrical Principles and Wiring Materials JTE2023 ELECTRICAL & ELECTRONIC TECHNOLOGY

  2. + Duracell Direct Current DC • a circuit containing a battery is a DC circuit • in a DC circuit the current always flows in the same direction

  3. Alternating Current (AC) • In an AC circuit the current reverses direction periodically • AC is what you get from the power companies

  4. Electrical Safety • Shock and Fire • Never disconnect any safety device • Don’t touch electrical items with wet hands or feet • Discontinue use of extension cord that feels warm • Don’t put extension cords under carpet

  5. Electrical Safety • Install wiring according to regulations • Determine cause of blown fuse or breaker • Don’t replace fuse with larger fuse • Don’t leave heat producing appliances unattended • Heaters & lamps away from combustibles • Don’t remove back of TV (30,000v when off)

  6. Electrical Safety • Keep appliances dry • Don’t use damaged switches, outlets, fixtures, extension cords • Follow manufacturer’s instructions for installation and use of electrical equipment

  7. Service Entrance • Power from from power company • Transformer: drops volts from 25,000 volts to 240 volts • Service drop: wires etc from transformer to house • Entrance head: weather-proof at house • Meter: $$$ • Service Entrance Panel (SEP): box with fuses or breakers

  8. Electric Meter • Kilowatthours: how electricity is sold • Kilo = 1000 • Watthour = use of 1 watt for one hour • 100 watt light bulb for 1 hour - 100 watthours • Kilowatthour = 1000 watts for one hour

  9. Voltage Drop • loss of voltage as it travels along a wire • lights dim, motors overheat • larger wires have less voltage drop for a given amount of current • longer wire = greater problem • must increase wire size as distance increases

  10. Wire Identification • Type of outer covering, individual wire covering, cable construction, number of wires • Wire type stamped on outer surface

  11. Switches • To control whether current is ON or OFF in the circuit. • Closed switch has zero resistance • Open switch has infinite resistance

  12. Cont. • Type of toggle switch: • SPST-Single-pole, single throw • SPDT-Single-pole, double throw • DPST-Double- pole , single throw • DPDT- Double-pole, double throw • Push-button • NO-Normally open • NC-Normally close

  13. Fuse and Circuit Breakers • When a wire carries more current than it should, it is said to be “overloaded”. To prevent overloading, fuses or circuit breakers are installed in circuits. They act like switches to open the circuit when the current exceeds some particular value.

  14. Fuse • An electrical protective device consisting of a fusible (easily melted) metal-alloy strip of wire encased in a cartridge • If current exceeds a predetermined value, sufficient heat is generated to melt the fuse causing an open circuit • Protects the circuit from possible damage due to excessive current

  15. Circuit Breaker • An electrical device that opens when the current exceeds a predetermined value for the circuit • Circuit breakers trip open, and may be reset when the operators are ready to close the circuit breaker • Circuit breakers may be operated manually or electrically, and can be used as switches in some circuits

  16. Circuit overload • if you have too many things plugged into the same circuit, the voltage may drop. • you may notice that a lamp plugged into the same outlet as a hair dryer dims a bit when you turn on the hair dryer because a hair dryer draws a lot of current • according to Ohm V = I R, a big I can cause enough drop in the voltage to be noticeable!

  17. Fuse and Circuit Breakers

  18. Function of Fuse • For example, a 20 A fuse or circuit breakers opens when the current passing through it exceed 20 A. This maybe due to too many devices drawing current in that circuit or there might be a fault such as short circuit somewhere.

  19. Example • Will the fuse blow? Determine the total current drawn by all the devices in the circuit. • I = P / V • Light bulb : 100W / 120V = 0.8 A • Heater : 1800W / 120V = 15.0 A • Stereo : 350 W / 120V = 2.9 A • Hair Dryer : 1200 W / 120 V = 10.0 A • So the total current used are 0.8 A + 15.0 A + 2.9 A + 10.0 A = 28.7 A

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