E1 – Electrical Fundamentals # 3 – Meters, Circuits, Loads and Switches

Meter Types Voltmeter – measures voltage Ohmmeter – measures resistance (ohms) Ammeter – measures current (amps) Multimeter – a combination meter that measures volts, ohms, & amps © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

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) © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Using a Voltmeter Line Voltage 120V Load © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

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 © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

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) © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Using a voltmeter to check switch contacts Checking switches with power on the circuit The voltmeter can show whether they are open or closed © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Checking Switches with a Voltmeter Line Voltage 240V Open ? Or ? Closed Switch Load Switch Switch Closed Switch Open © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Checking for “Continuity” Determine if the wiring within a load is continuous Example: Checking a resistance heater © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

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 © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Ammeters (Amp Meters) Current flow creates a magnetic field Ammeters measure the intensity of the field © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

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 © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

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 © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Measuring Current Flow Neutral 120 v COM V/  V AC DC Power ON Power OFF Heater energized Hot Current flow No current © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0 OFF V AMPS Ω

Determining Circuit Resistance An ohmmeter measures resistance Ohm’s law calculates resistance Measuring and calculating work together © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Measuring and Calculating Resistance Check voltage first Disconnect wires Now Check resistance Neutral 120 v Power ON Power OFF 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) © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

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. © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Series Circuits A string of "old-fashioned " Christmas tree lights is an example of a series circuit. 120v © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

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. © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

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 © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

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 © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Calculating Series Circuit Amperage Ohm’s Law: I = E  R or Amps = Volts  Ohms L1 120 Volts R1 = 4 Ω R2 = 10 Ω Rt = 40 Ω 120 V 40 Ω R4 = 14 Ω R3 = 12 Ω N Itotal =  = 3 Amps © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Measuring Series Circuit Amperage It = I1 = I2 = I3 = I4 = 3 Amps L1 120 Volts R1 = 4 Ω R2 = 10 Ω Rt = 40 Ω R4 = 14 Ω R3 = 12 Ω N It = 120v  40Ω = 3 Amps © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0 OFF V AMPS Ω OFF V AMPS Ω OFF V AMPS Ω

Calculating Voltage in Series Circuits All loads share the available voltage The total voltage is the sum of all the voltage drops across each load: Etotal = E1 + E2 + E3 + E4 +… © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Calculating Voltage Drop in a Series Circuit The voltage drop across each load is E = IR, or volts = amps x ohms L1 N 120 Volts E1 =3A x 4Ω=12v 12v E2 =3A x 10Ω=30v 30v E4 =3A x 14Ω=42v 42v E3 =3A x 12 Ω=36v 36v Et = + + + = 120v © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0 OFF V AMPS Ω

Measuring Voltage in Series Circuits All loads share the available voltage The voltage of each load drops as more loads are added © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

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. © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

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. © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

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 © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

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 © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Amperage in Parallel Circuits The resistance of each load determines the amperage of each circuit. Additional loads increase total amperage. © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Calculating Amperage in Parallel Circuits E = IR I = E  R Amps = Volts  Ohms L1 L2 120 Volts I1=120v/4Ω I1= 30A I3=120v/12Ω I3= 10A 30A 10A I2=120v/10Ω I2= 12A I4=120v/14Ω I4 = 8.6A 12A 8.6A Itotal = I1 + I2 + I3 + I4 + … Itotal = + + + = 60.6A © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Measuring Amperage in Parallel Circuits An ammeter Measures each circuit Also verifies total amperage © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Measuring Amperage in Parallel Circuits Each circuit is measured. Amperage increases with the number of loads. L1 L2 120 Volts I1=120v/4Ω I1= 30A I3=120v/12Ω I3= 10A I2=120v/10Ω I2= 12A I4=120v/14Ω I4 = 8.6A Itotal = I1 + I2 + I3 + I4 + … Itotal = 30A + 12A + 10A + 8.6A = 60.6A © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0 OFF V AMPS Ω OFF V AMPS Ω OFF V AMPS Ω OFF V AMPS Ω OFF V AMPS Ω OFF V AMPS Ω OFF V AMPS Ω

Calculating Voltage in Parallel Circuits The voltage can be calculated, if the amperage and resistance are known. In parallel circuits the voltage is the same throughout the circuits. © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Calculating the Voltage for Parallel Circuits E = IR Volts = Amps x Ohms L1 L2 E1=30Ax4Ω E1= 120v 120 Volts E3=10Ax12Ω E3= 120v E2=12Ax10Ω E2= 120v E4=8.6Ax14Ω E4= 120v Etotal = E1 = E2 = E3 = E4 = 120v © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Single Load Resistance in a Parallel Circuit One load provides the only path for current flow Its resistance is the total circuit resistance The following slide compares resistance to crossing a river Resistance is the open space between the shores Cars represent electrons Bridges represent loads © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Single Load Single Electron Path Single Resistance Single Load © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Two Loads in a Parallel Circuit Two loads provide two paths for electrons More total current flow than a single circuit The total resistance is less than that for a single load © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Two Loads More Electron Paths Less Resistance Two Loads © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Total Resistance in a Parallel Circuit For Two resistances: Rtotal = (R1 x R2)  (R1 + R2) R1 = 4Ω R2= 10Ω L1 L2 4 Ω 4 Ω 10 Ω 10 Ω Rtotal=( x )  ( + ) R1 R1 R2 R2 =(40 Ω)  (14 Ω) = 2.86 Ω © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Three Loads in a Parallel Circuit Three loads provide three paths for electrons More total current flow than with one or two circuits Because the total resistance is less than with only one or two loads The total resistance decreases as the number of loads increase © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

total resistance decreases! Three Loads Three Loads More Electron Paths With more loads total resistance decreases! © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Multiple Resistances in a Parallel Circuit For 3 or more resistances: Rtotal = 1/R1 + 1/R2 + 1/R3 + 1/R4… R1 = 4Ω R2= 10Ω L1 L2 R3 = 12Ω R4 = 14Ω 4 Ω 12 Ω 10 Ω 14 Ω Rt = 1/ + 1/ + 1/ + 1/ = R1 R2 R3 R4 .50 Ω © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

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. © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

A/C-Heating Unit Parallel Circuits Load 1 Electric Heater Load 2 Load 3 Load 4 Evap Mtr Comp Cond © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Diagram Development A schematic diagram is also called a “ladder diagram” The rungs of the ladder are parallel circuits © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

A/C-Heating Unit Parallel circuits Schematic Diagram A/C-Heating Unit Parallel circuits (Ladder Diagram) Load 2 Load 3 Load 4 Evap Mtr Comp Cond L2 L1 Load 1 Electric Heater Load 2 Load 3 Load 4 Evap Mtr Comp Cond L2 L1 Load 1 Electric Heater © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Diagram Set-Up The lift side is usually considered the main power The right side is usually considered common © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

Schematic Diagram Electric Heater Evap Mtr Comp Cond (Ladder Diagram) 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”. © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

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. © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

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 © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0

END OF Meters, Circuits, Loads & Switches © 2005 Refrigeration Training Services - E1#3 Meters, Circuits, Loads & Switches v1.0