“Electrical Fundamentals”

Always Remember, Safety is #1 and Everyone’s Business!

Use Safety Equipment

Remove Jewelry

Do not wear rings or jewelry when working on electrical circuits. ELECTRICAL BURNS Do not wear rings or jewelry when working on electrical circuits. Never use screwdrivers or other conductive tools in an electrical panel when the power is on.

Lift and Move Correctly

High voltage is always dangerous. Electric Shock BE CAREFUL! High voltage is always dangerous. Even 40 volts can be lethal if skin is wet or damaged.

Current is the killing factor in electrical shock. Currents between 100 and 200 mA generally cause the heart to fibrillate. A 110 volt power circuit will generally cause between 100 and 200 mA current flow through the bodies of most people.

LOCKOUT – TAGOUT PROCEDURES Whenever a piece of equipment is being worked on, it should be disconnected from the power source and locked. The person working on the equipment should carry the only key to prevent accidental activation.

DO NOT WORK ALONE If you must test a live circuit, have someone with you ready to turn off the power, call for help, or give cardiopulmonary resuscitation (CPR).

LEARN FIRST AID Anyone working on electrical equipment should take the time to learn CPR and first aid.

NON-CONDUCTING LADDERS Aluminum ladders can be hazardous if they come in contact with power lines. Fiberglass or wood ladders should be used.

Fuses and breakers are used to protect wires, not people. CIRCUIT PROTECTION Fuses and circuit breakers are used to protect a circuit against over current. The amperage rating of a fuse must not be greater than the ampacity of the wires being protected. Fuses and breakers are used to protect wires, not people.

“Power is the rate at which work is done.”

Calculating Electrical Power “Power is the rate at which work is done.” Power = Intensity x Electromotive force P = IE Power (watts) = Amps x Volts

Power (watts) = Amps x Volts Power = Intensity x Electromotive force What is the power consumption of an electric circuit using 15 amperes and 120 volts? Power (watts) = Amps x Volts Power = Intensity x Electromotive force P = IE P = 15 amps x 120 volts P = 15 x 120 P = 1800 Watts

Power (watts) = Amps x Volts Power = Intensity x Electromotive force What is the current of an electric heater rated at 4800 watts on 240 volts? Power (watts) = Amps x Volts Power = Intensity x Electromotive force P = IE solve for I P  E = I 4800 watts  240 volts = I (amps) 4800  240 = 20 Amps

Ohm’s Law Wheel All applications of Ohm’s Law formulas can be represented as the spokes of a wheel.

E is Electromotive force in Volts Ohms Law Wheel P is Power in Watts I is Intensity in Amps E2 R E R I2 R P E IE P R P E I R E .I PR P .I E2 P P I2 IR R is Resistance in Ohms E is Electromotive force in Volts

Resistance & Loads Resistance: Loads: Opposition to electron flow in the circuit Measured in ohms (Ω) Loads: Must have some resistance Provide a path for electron flow

Compare Resistance To Crossing A River Resistance is the open space between the shores Cars represent electrons Bridges represent loads Without bridges there is no way the cars can cross This is known as “infinite” resistance

Infinite Resistance

A Load Is Added The load provides a path for electrons There is still high resistance to flow But it is no longer infinite resistance

A small load provides a path for some of the electrons But there is still High Resistance

More Load Is Added Less resistance More electron flow

Lower resistance means more electrons, or current flow. The resistance is lower

Low Or No Resistance Can Be Bad The lower the resistance, The higher the electron flow If the current flow is out of control, The circuit is overloaded

OVERLOAD If resistance is too low, electron flow will be too high.

Resistance, Watts, And Amps Load resistance affects amps and watts The lower a load’s resistance The higher it’s amps and watts

How Resistance Affects Amps and Watts (Note: approximate values in an alternating current 120v circuit) OPEN L1 N Infinite Resistance ∞ Ohms (R) No Watts (P) No Amps (I) 1500 Ohms .08 A 10 W 150 Ohms .8 A 100 W 15 Ohms 1000 W 8 A BOOM High Watts & High Amps Circuit Breaker Trips 0 Ohms

Direct Current Moves in one direction Negative to positive Can be produced through chemical action Chemical electrolyte produces electrons Negative cathode gives away electrons Positive cathode collects electrons

Direct Current (DC) Electrolyte Zinc Case (Negative Electrode) Carbon Rod (Positive Electrode) Dry Cell Battery When load is attached the chemical reaction in the electrolyte causes current flow

Alternating Current (AC) Moves in one direction, then the other Produced by a generator

Alternating Current (AC) Generator Generators produce Alternating Current First, the current goes in one direction Then it reverses, or alternates, in the opposite direction

Alternating Current (AC) Generator In the U.S. there are 60 complete cycles per second

Cycles and Frequency Cycle: Frequency Measurement of frequency: One complete electrical alternation Frequency Number of cycles in a second Measurement of frequency: Hertz (Hz) Cycles U.S. frequency is 60 hertz, or 60 cycles

Generating Alternating Current (AC) Passing a conductor through a magnetic field. A generator uses many conductors and a large magnetic field to produce electrical current.

Generating Alternating Current (AC) Passing a conductor through a magnetic field. A generator uses many conductors and a large magnetic field to produce electrical current.

Generating Alternating Current Magnet NORTH Passing a conductor between two magnets causes electrons to flow in the wire. This produces electrical current in the wire. SOUTH Magnet Conductor

Expressing AC with a Sine Wave A sine wave shows how alternating current flows in one direction, then reverses to flow in the opposite direction.

Sine Wave of Alternating Current Magnet 0º 90º 180º 270º 360º NORTH Positive Negative SOUTH Magnet One cycle Conductor

Alternating current starts at 0, reaches a peak, then returns to 0 Effective voltage Alternating current starts at 0, reaches a peak, then returns to 0 Peak voltage at 90° (electrical degrees)

Generating 3 Phase Alternating Current 3Ø current is generated by passing three conductors through a magnetic field

Generating 3Ø Current Magnet NORTH Current is generated in each conductor as it passes through the magnetic field. SOUTH Magnet

Sine Wave of 3 Phase Current Magnet 0º 120º 240º 360º NORTH 90º 180º 270º SOUTH Magnet Each sine wave starts 120° after the other.

Sine Wave of 3 Phase Current Magnet 0º 120º 240º 360º NORTH 90º 180º 270º SOUTH Windings 120° out of phase give 3Ø motors their high starting torque. Magnet

Meter Types Voltmeter – measures voltage Ohmmeter – measures resistance (ohms) Ammeter – measures current (amps) Multimeter – a combination meter that measures volts, ohms, & amps

Voltmeters Measure electromotive force of a circuit in volts Always set meter at the highest voltage scale to prevent meter damage 1 Volt = 1,000 millivolts (mV)

Using a Voltmeter Line Voltage 120V Load

Ohmmeter The meter uses an internal battery to push voltage through a device. The resistance encountered by the battery’s current is measured in ohms. Open: Infinite resistance (∞ or OL) Example: Switch open, broken wire, etc. Closed or Short: No resistance (0) Example: Switch closed, wires connected, or shorted winding Measurable resistance: Any value between 0 - ∞ Example: Resistance of a motor winding or heater wire

How to Read an Ohmmeter How to Read an Ohmmeter No Resistance (Short or closed circuit) Infinite Resistance (Broken wire or open switch) Measurable resistance Good for loads (coils, heaters, and motors)

Using a voltmeter to check switch contacts Checking switches with power on the circuit The voltmeter can show whether they are open or closed

Checking Switches with a Voltmeter Line Voltage 240V Switch Open ? Or ? Closed Switch Load Switch Closed Switch Open

Checking for “Continuity” Determine if the wiring within a load is continuous Example: Checking a resistance heater

Prove heater wire is broken Checking Continuity Prove heater wire is broken Disconnect wires Neutral 120 v Power OFF 1200 Watt Heater COM V/  V AC DC Hot Disconnect wires An open circuit has infinite resistance

Current flow creates a magnetic field Ammeters (Amp Meters) Current flow creates a magnetic field Ammeters measure the intensity of the field

Measuring Current in Amperes Power In Current produces a magnetic field OFF V AMPS Ω Ammeter measures the intensity (I) of the magnetic field AMPS

Using an Ammeter Current intensity is measured in amperes 1 Amp = 1,000 milliamps (mA) Most common ammeter is a “Clamp-on” type Meter jaws must encircle only one wire

Measuring Current Flow Neutral 120 v COM V/  V AC DC Power ON Power OFF Heater energized Hot Current flow No current OFF V AMPS Ω

Determining Circuit Resistance An ohmmeter measures resistance Ohm’s law calculates resistance Measuring and calculating work together

Measuring and Calculating Resistance Check voltage first Disconnect wires Now Check resistance Neutral 120 v Power OFF Power ON 1200 Watt Heater 120 v 1200W COM V/  V AC DC Hot Heater resistance is 12Ω Disconnect wires Calculating Resistance using Ohm’s Law: P = E I or Watts = V x A E = IR 120v = I = P E E I R = = = 10A (amps) 10A = 12Ω (ohms)

Series Circuit Only one path for electrons to flow. Current must be able to go through one device before it can go to the next device.

Series Circuits A string of "old-fashioned " Christmas tree lights is an example of a series circuit. 120v

Resistance in Series Circuits The more loads in a series circuit, the more resistance in the circuit Total resistance is the sum of all the resistances in the circuit.

Calculating Series Circuit Resistance Rtotal = R1 + R2 + R3 + R4 + … L1 R1 = 4 Ω 4 Ω R2 = 10 Ω 10 Ω R4 = 14 Ω 14 Ω R3 = 12 Ω 12 Ω N Rt = Rt = + + + = 40 Ω 40 Ω

Amperage in series circuits The more loads in a series circuit, the greater the total resistance The greater the resistance, the lower the total amperage (I = E/R or A = V/R) The amperage will be the same everywhere in the circuit

Bulb dims as more bulbs are added COM V/  V AC DC COM V/  V AC DC COM V/  V AC DC L1 120v N Why does adding bulbs to the circuit make them all dimmer? Because there is less voltage available to each bulb.

What happens when a series circuit is opened? Why? All loads are de-energized because the flow of current is interrupted. 120v 120v No current flow Circuit is open L1 N L1 N 120v That is why switches and controls are in series with the loads they control.

Parallel Circuits Loads are parallel to each other, not in series There is more than one path for electrons to flow Therefore: Each load receives full voltage Each load can operate independently

Measuring voltage in parallel circuits COM V/  V AC DC COM V/  V AC DC COM V/  V AC DC L1 L2 R1=4Ω R2=10Ω Each load receives the same voltage

Amperage in Parallel Circuits The resistance of each load determines the amperage of each circuit. Additional loads increase total amperage.

Simple Diagram of Parallel Circuits The following slide shows how the loads in an air conditioning unit with electric heat might be sketched into a simple diagram.

A/C-Heating Unit Parallel Circuits Load 1 Electric Heater Load 2 Load 3 Load 4 Evap Mtr Comp Cond

A schematic diagram is also called a “ladder diagram” Diagram Development A schematic diagram is also called a “ladder diagram” The rungs of the ladder are parallel circuits

A/C-Heating Unit Parallel Circuits (Ladder Diagram) Load 2 Load 3 Load 4 Evap Mtr Comp Cond L2 L1 Load 1 Electric Heater Schematic Diagram Load 2 Load 3 Load 4 Evap Mtr Comp Cond L2 L1 Load 1 Electric Heater

Diagram Set-Up The lift side is usually considered the main power The right side is usually considered common

Schematic Diagram (Ladder Diagram) Electric Heater Evap Mtr Comp Cond Load 2 Load 3 Load 4 Load 1 Evap Mtr Comp Cond Electric Heater The left side (L1) is the “hot” side The right side (L2) is the “common” side. On a 120v circuit this side would be the “neutral”.

Series – Parallel Circuits Controls and switches are in series with loads An open switch stops current to any load in that one circuit. A disconnect switch in the main power line stops current to all circuits after it.

Series - Parallel Circuits Load 2 Load 3 Load 4 Load 1 Evap Mtr Comp Cond Electric Heater A disconnect switch A heating thermostat in series with the heater A cooling thermostat and pressure control in series with the compressor

Electrical Loads Loads Examples: Consume electricity Do work Motors Solenoids Heaters Lights

(Letters tell what motor is represented) Motors Common symbols: (Letters tell what motor is represented) COMP EFM IFM COMP EFM IFM COMPressor Evaporator Fan Motor Indoor Fan Motor COMP CFM OFM CFM OFM COMP Condenser Fan Motor Outdoor Fan Motor

Solenoid When current flows through a coil of wire it creates a magnetic field. This will cause an action in a relay or valve. Electrical symbol for a solenoid coil:

Magnetic coil energized Solenoid Valve Magnetic coil energized Plunger pulled up Power off Plunger drops This solenoid valve is in the NC (normally closed) position. The flow of liquid or vapor is stopped. When the magnetic coil is energized the plunger is raised and fluid passes under the disk and through the pipe in the direction of the arrow stamped on the side of the valve. Fluid flows Plunger Fluid stops Seat

Heaters Convert electrical energy to heat Symbol for resistance heaters: Examples of heaters: Auxiliary strip heaters Crankcase heaters

Signal Lights B R G R Red B Blue G Green, etc. Used to show when something is operating, or when there is a problem. Symbol for signal lights: B R G Letter in the center denotes bulb color: R Red B Blue G Green, etc.

Contactor It is a mechanical switch, operated by a magnetic coil Energizing the coil closes the contacts Power flows through the contacts to the load

Contactor Cutaway LINE 1 Power In CONTROL CIRCUIT 2 Coil 3 Contacts LOAD CONTROL CIRCUIT LINE 1 Power In 2 Coil 3 Contacts 4 Power Out

Symbols for Contactors Coil Contact Single pole Double pole Triple pole 115v 208-230, 1 208-230, 3 Symbols are shown “de-energized” (no power) with contacts “normally open”. © 2005 Refrigeration Training Services - E1#4 Symbols and Wiring Diagrams v1.0

Visualizing Symbols With Power On The following slide illustrates what happens when the power is turned on.

Contactor coil “Energized” Contacts close Coil Contact Single pole Double pole Triple pole 115v 208-230, 1 208-230, 3

Relays Similar to contactors Usually under 20 amp capacity Contacts may be: Normally open (NO) Normally closed (NC) Or a combination of NO and NC

Coil “de-energized” (no power) Symbols for RELAYS Coil “de-energized” (no power) Normally Open “NO” 1 2 1 2 3 Single pole Double pole Triple pole #1 NO #2 NC #1 NC #2 NO #3 NC Normally Closed “NC”

Visualizing Symbols With Power On The following slide illustrates what happens when the power is turned on.

Coil “energized” (powered up) Symbols for RELAYS Coil “energized” (powered up) Normally Open “NO” 1 2 1 2 3 Single pole Double pole Triple pole #1 NO #2 NC #1 NC #2 NO #3 NC Normally Closed “NC”

Introduction to Switches Switches open and close contacts to control a load Contact: the conducting part of a switch Poles: the number of contacts in a switch Throw: the number of closed contact positions per pole.

Single Throw Switch Symbols Switch open Switch closed Single Pole – Single Throw (SPST) L1 Switch open Switch closed L2 Double Pole – Single Throw (DPST)

Double Throw Switches Each switch position closes a circuit

Single Pole - Double Throw (DPDT) Contacts 1-2 closed Contacts 1-2 open 2 1 Contacts 1-3 open Contacts 1-3 closed 3

Double Pole – Double Throw (DPDT) Contacts 1-2 closed Contacts 1-3 closed 2 1 3 5 Contacts 4-5 closed 4 6 Contacts 4-6 closed

Thermostats COOL OFF HEAT ON FAN AUTO B O W Y G R 70 80 60 50 Symbol depicts a bimetal spring which closes and opens the contacts. Tstats are usually shown in their “normal” position, which is open.

Symbols for Thermostats Cooling thermostat In actual operation As the temperature goes up the rise in temperature causes the bimetal to expand the expanded bimetal raises the arm the raised arm closes the contacts

Symbols for Thermostats Heating thermostat In actual operation As the room temperature falls the fall in temperature causes the bimetal to contract the contracted bimetal pulls down on the arm the arm closes the contacts

Pressure Controls Symbol depicts a bellows which operates the contacts. Pressure safety controls are usually shown in their “normal” position, which is closed.

Symbols for Pressure Controls Low pressure control In actual operation As the system pressure falls the fall in pressure causes the bellows to deflate the deflated bellows pulls down on the arm the arm opens the contacts

Symbols for Pressure Controls High pressure control In actual operation As the system pressure rises the rise in pressure causes the bellows to inflate the inflated bellows raises the arm the raised arm opens the contacts

Fuses and Overloads Symbols for safety devices, such as fuses and overloads, are usually shown closed.

Safety Device Symbols Fuses Overloads Bimetal overload: High heat and high amperage open this overload switch. Thermal overload relay: Excessive amperage heats the thermal element, which opens the switch. Magnetic overload relay: Excessive amperage creates a magnetic field, which opens the switch.

Next Month – Understanding & Troubleshooting Wiring Diagrams Schematic Diagrams Next Month – Understanding & Troubleshooting Wiring Diagrams

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