Agricultural Systems Technology II Electrical Wiring Agricultural Systems Technology II

Objectives Objective A: Explain the characteristics and measurement of electricity. Objective B: Install basic electrical circuits.

What is electricity? Electricity is the movement or flow of electrons in a conductor. Resistance: tendency of a material to prevent electrical flow Conductor: material that allows electricity to flow easily (Gold, Silver, Copper and Aluminum) Insulator: material that provides great resistance to electrical flow (Rubber, Glass, Vinyl and Air)

How do I measure electricity? Amperes: measure of the rate of flow of electricity (or current) Volts: measure of electrical pressure Watts: measure of the amount of power or work that can be done Power equation: W=VA Shows the relationship between watts, volts and amps.

Power Equation Watts = Volts x Amps A light bulb that uses 5 amps on a 120 volt circuit uses how many watts of power? W = 120v x 5a W = 600 watts V = W/A A = W/V

Ohm’s Law Relationship between resistance, volts and amps Ohm (the unit of resistance)= R Volts (electromotive force)= E Amps (inductance)= I Ohm’s Law: E = IR I=E/R R=E/I

Current Alternating current – electrons flow in both directions, changing rapidly Used in buildings, houses Direct current – electrons flow in one direction only Used in vehicles, equipment powered by batteries

Electrical Safety Shock and Fire Never remove any safety device Don’t touch electrical appliances or wiring with wet hands or feet Don’t remove ground plug prong Use GFI in wet areas Stop using extension cord that feels warm or smells like burning rubber Don’t run extension cords under carpet

Electrical Safety Always install wiring according to NEC Tripped breaker or fuse determine cause before resetting Don’t replace fuse with larger fuse Don’t leave heat producing appliances unattended or use near combustible material Ground all metal cases and cabinets of electrical appliances

Electrical Safety Don’t use cracked or damaged switches, outlets, fixtures or extension cords Follow all manufacturer’s instructions for installation and use of all electrical equipment

What is a circuit? Electricity must flow in a circle called a circuit Open circuit = circle is broken Short circuit = no load, current increases and wires overheat/melt. Fuses or circuit breakers prevent damage to wires if too much current, trip or blow

Service Entrance Power from from power company Transformer: drops volts from 25,000 volts to 240 volts Service drop: wires from transformer to house Entrance head: weather-proof at house Meter: Measures electricity use Service Entrance Panel (SEP): main box with fuses or breakers

Electric Meter Energy: amount of power used over time Kilowatt-hours: how electricity energy is measured and sold Kilowatt = 1000 watts Watt-hour = use of 1 watt for one hour 100 watt light bulb running for 1 hour = 100 watthours Kilowatt-hour = 1000 watts for one hour

Branch Circuits usually begin at SEP branch out into a variety of places only 1 motor or several outlets or several lights use correct size wire and fuse or breaker Load determines wire size, wire size determines breaker size

Types of Cable Nonmetallic sheathed cable: copper or aluminum wire covered with paper and vinyl for insulation Armored cable: flexible metal sheath with individual wires inside, wires are insulated. Good against physical damage, bad in damp areas Conduit: tubing with individually insulated wires, required for commercial jobs

Wire Type and Size Copper aluminum use one size larger No 14 (14 gauge) = 15 amp circuits No 12 = 20 amps No 10 = 30 amps aluminum use one size larger lower gauge number = thicker wire No 8 and larger use bundles of wires current travels on outer surface of wire, so a bundle of smaller wires can carry more

Wire Identification Wire type stamped on outer surface Color coded: black or red is the hot wire that carries current to appliances White = neutral wires carry current from appliance back to source Green or Bare = ground all metal boxes and appliances for safety

Wire Identification Wire Size: 12-2 has two strands of No. 12 wire (black & white) 12-2 w/g adds one green or bare 12-3 has three strands of No. 12 (black, red, white) 12-3 w/g adds one green or bare

Voltage Drop Loss of voltage as it travels along a wire Caused by resistance Lights dim, motors overheat, electronics damaged Larger wires have less voltage drop for a given amount of current Longer wire = greater resistance, more drop Larger wire size must be used to overcome drop on a long wire

Objective B: Install Basic Circuits Conductors of correct size for load Boxes contain all electrical connections Cable must be secured to box Box must be secured to building

Basic Rules for Wiring Metal box must be grounded Splice wires in boxes with wire nuts, no bare wires (except safety ground) Only 1 wire to each terminal Hot wire (black or red) attach to brass or black terminal Neutral wire (white) attach to silver terminal Ground wire attach to box or green terminal

Basic Rules for Wiring If white wire used as hot must be marked with black paint or tape All connections tight and secure to prevent spark or short Receptacle – device for receiving plugs Switch – device for interrupting flow of electricity Always place switch on hot side of circuit (black or red wire)

Duplex receptacle circuit

Single switch light circuit

3 way switch circuit (2 locations)

Testing circuits Use continuity or Ohmmeter If circuit complete then beep or reading If open then none Turn off voltage in circuit

Testing Procedure Turn all switches to on Remove bulbs Place probes on black and white wires at source(disconnected) Correct if no reading

Testing Procedure Put light bulb in last fixture Repeat test Should be a reading if bulb and circuit are good Last test for grounded boxes One probe on metal box One probe on ground (safety wire at source) Should be a reading

Source: Agricultural Mechanics: Fundamentals and Applications by Ray V. Herren. 2010, Delmar Cengage Learning, Clifton Park, NY.