Advanced Electrical Troubleshooting: Chapter 3
Content
Electrical Inspections - Switches
In this module, we will learn about a common circuit component: switches. By the end of the module, you will be able to:
- Troubleshoot switches. Skip to quiz!
Switches
A switch is anything that is used to make or break an electric current in a circuit. It consists of electrical contacts, which are metal strips inside the switch to make or break a connection in the loop.
When the switch is open, the contacts are not connected, and electricity cannot flow. When the switch is closed, the contacts are connected, and electricity flows through the loop.
Switches are classified based on the number of poles and throws. A pole is the number of circuits that a single switch can operate. A throw is the number of contacts a switch can change to in one circuit.
There are several types of switches:
SPST: single pole single throw
SPDT: single pole double throw
DPST: double pole single throw
DPDT: double pole double throw
How to Inspect a Switch
To inspect a switch, we first need to take the switch out so that the terminals are exposed. We will use a multimeter on the AC voltage setting to check voltages across the switch.
Make sure that the hot and ground terminals are visible on the switch. The hot terminal will be gold, and the ground terminal is green.
The switch must initially be in the off or open position. Connect the red multimeter probe to the lower hot terminal of the switch and the black probe to the ground terminal. The multimeter should display a value of 110-120V (for the US).
Next, change the red probe to the upper hot terminal of the switch and keep the black probe on the ground. The multimeter should show 0V because the switch is open, and electricity should not flow across it. If there is a voltage value, the switch is faulty.
Disconnect the switch and set the multimeter to the Ω setting. Attach the multimeter probes to both the upper and lower terminals of the switch. The multimeter should read “OL” or 1, which shows an open loop. Any other reading would show a faulty switch.
Now we will test the switch in the on or closed position. First, connect the red probe to the lower hot terminal and the black probe to the ground. The multimeter should read 110-120V, just like when the switch is open.
Next, change the red probe to the upper hot terminal of the switch and keep the black probe on the ground. The multimeter should also display 110-120V because the switch is closed, and electricity should flow across it. Any other reading would show a faulty switch.
With the switch still on, set the multimeter to the Ω setting. Attach the multimeter probes to both the upper and lower terminals of the switch. The multimeter should read a value close to zero, which shows a complete loop. Any other reading would show a faulty switch.
In this module, we learned about switches. Switches are responsible for making or breaking electric current in a circuit.
We also learned the process of troubleshooting switches. A faulty switch will show an OL or 1 in on the state. A faulty switch will also show a finite resistance in the off state.
Electrical Inspections - Contactors
In this module, we will learn about a common circuit component, contactor. We will also be able to troubleshoot contactors. Skip to quiz!
Contactors
Contactors are similar to switches but are controlled electrically. They are very similar to relays, but contactors can carry huge currents compared to a relay. Relays can carry only a few amperes, whereas contractors carry up to 12,500 A.
Contactors have higher current and voltage switching capabilities. Recall that current and voltage switching means performing the switching when the current or voltage is zero. They do not provide short-circuit or overload protection, but they can break the contact if the coil excites.
Contactors are typically used to connect and break power supply lines. Recall that breaking means disconnecting. They are usually used in different loads, but the complex machine controls such as motors, transformers, and heaters.
How to Inspect Contactors
The most important step before inspecting a contactor is to disconnect it from all power sources. Depending on its use, the contractor may have a few different power sources. We will use a multimeter on the Ω setting while inspecting a contactor.
We should first check the contactor in the OFF or open position. Connect the multimeter probes to the line and lead terminals of the contactor. Recall that line and lead terminals in a single-pole contactor may be identified by L1 and T1.
The contactor is faulty if the multimeter displays anything other than OL or 1 , since the switch may be stuck closed. If the contactor is having more than one terminal, we should check all terminals.
Next, we should check the contactor in the ON or closed position. Connect the multimeter probes to the line and lead terminals of the contactor. The multimeter should read a resistance value close to zero. This is because if the switch is closed, the circuit is a complete loop.
If the multimeter reads “OL or 1,” then the contactor is faulty. This is because if the switch is closed, the circuit is a complete loop. Make sure you check all terminals if there are multiple.
Contactors are switches that are controlled electrically. In the OFF state, the multimeter must show an OL or 1 across the terminals of a functional contactor. In the ON state, the multimeter must show a low resistance across the terminals of a functional contactor.
Electrical Inspections - Heater
In this module, we will learn about a common HVAC appliance resistance heaters. By the end of the module, you will be able to inspect resistance heaters. Skip to quiz!
Resistance Heaters
Most portable heaters, like the one shown in the photo, are electric resistance heaters. Resistance heaters turn electrical energy into heat energy.
Resistive heating is the process of passing current through a resistor such that it releases heat. The higher the resistance encountered, the more heat will be released.
The resistive heating is governed by the simple formula Q = I² ✕ R ✕ T
‘Q’ is the amount of heat.
‘I’ is the current flowing through the conductor.
‘R’ is the resistance of the conductor.
‘T’ is the time for which the current was passed.
If the resistance offered is too high, no electricity passes through the material. Therefore, higher resistance may release no heat at all. Picking a suitable resistive material for a heating element is critical for maximizing heat output while minimizing energy costs.
How to Inspect Resistance Heaters
When inspecting a resistive heater, first make sure the power supply is off and has had enough time to cool to avoid burns. You can usually use circuit breakers for a larger heating unit. We will be using a multimeter on the Ω setting to check the heater.
Detach all electrical wires from the terminals of the heater. This will isolate the terminals so that we can check them all individually.
Connect multimeter probes across both the ends of the resistance heater. If the multimeter displays a finite resistance value, the heater is working properly. If there is an ‘OL’ or ‘1’ the heater is faulty. Repeat these steps for the other remaining terminals.
Resistance heaters are elements that turn electrical energy into heat energy. For a working heater the multimeter will display a finite resistance. Whereas for a faulty heater, the multimeter will display an OL or 1.
Safety Inspections - Part 1
In this module, we will learn about the common electrical safety equipments. By the end of the module, you will know about basic safeties and how to troubleshoot them. Skip to quiz!
Fuses
A fuse is an electrical safety element designed to melt and separate in the event of an over-current. The fuse interrupts excessive current to prevent damages by overheating or fire.
The electric fuse is made of a low resistance conducting wire. The fuse wire is mounted between two conducting electric terminals. It is enclosed in a non-combustible tube.
The fuse wire is made up of copper, silver, or aluminum. When an excess current flows, the wire melts, resulting in an interruption of the current flow. This prevents the electrical components from damages.
How to inspect a fuse
When inspecting a fuse, always switch OFF the power supply. Check for any physical damages such as burnt marks etc at first.
A fuse is considered to be functional if it is continuous. Recall that while checking continuity, the multimeter dial must be set to the continuity setting. Connect the black and red connector to the COM and VΩ port.
Attach the probes across both the ends of the fuse. A long beep sound with a low resistance value indicates the fuse is functional. An ‘OL’ or ‘1’ across the fuse will indicate the fuse is faulty.
Safeties
Safeties in HVAC refers to the safety equipments. Some examples of safety equipments in HVAC are fuses, thermal overload switches, circuit breaker etc.
Recall that fuses are the element that protects the equipment in the event of an over-current. Thermal overload switches are present in the motors to prevent them from damages due to overheating. Similarly, circuit breakers are safety elements that interrupt the excess flow of current.
How to inspect a safety
Let’s learn how a inspect a thermal overload switch here. The thermal overload switch is connected in series to a power supply and a motor. In the event of an excessive heat, the switch will cut-off power to the motor.
In the normal state, the thermal overload switch contacts must be closed. Only after a specific temperature, the contacts must get opened. For inspecting a thermal overload switch, set the multimeter to the continuity setting.
Connect the multimeter probes/clips across the 1 and 2 terminals of the switch. The thermal overload switch is working if the multimeter produces a beep sound and shows a very low reading. In the cold state, terminals 1 and 2 of the switch are connected.
When the thermal overload switch has attained a certain temperature, the terminals 1 and 2 gets disconnected. The multimeter must display an ‘OL’ or ‘1’ here, otherwise the thermal overload switch is faulty.
Define an overload
Electrical circuits are designed to handle a specified amount of electricity. Whenever the current through an electrical circuit exceeds safe levels, it is said to be an overload. This unexpected increase in current levels may be due to a power surge or a fault.
The main signs of an overload in an electrical circuits are:
Tripping of circuit breakers
Shutting of other power sources
Burnt marks on switches, power outlets, etc.
How to an inspect overload
First, turn OFF all the switches and unplug the appliances plugged from the circuit. Locate the circuit panel and check if any of the switches in the panel have tripped.
Attempt to reset any tripped switches by turning them ON and OFF. If turning ON any of the switches trips the circuit breaker, the fixture or receptacle for that switch has a short circuit. Moreover, if turning ON one of the appliances trips the circuit, there may be an overload.
In this module, we learned about various safety equipment. Fuses are components that prevent the circuit in the event of an overcurrent. Safeties in HVAC are fuses, thermal overload switches, circuit breakers, etc.
We also learned about how to troubleshoot various safety equipment. An ‘OL’ or ‘1’ across a fuse will indicate it is faulty. In the cold state, the thermal overload switch must show a low resistance value and an ‘OL’ or ‘1’in the hot state.
Inspections - Part 2
In this module, we will walk through circuit breaker. By the end of this module, you will be able to troubleshoot circuit breaker. Skip to quiz!
Circuit Breaker
A circuit breaker is a switching device that can be operated manually or automatically to protect the electrical system. Recall that switches are devices used to interpret the power supply in a electrical circuit. It interrupts the flow of current (due to fault) and performs a switch's function.
Types of circuit breakers include:
Oil circuit breakers
Air circuit breakers
SF6 circuit breakers
Vacuum circuit breakers
Further on the basis of operation, the circuit breakers can be classified as:
Low voltage circuit breakers
Medium voltage circuit breakers
circuit breakers
High voltage circuit breakers
How to Inspect a Circuit Breaker
Unplug or switch OFF all the electrical appliances connected to the breaker. Check for any physical damages such, as burnt marks in the circuit breaker.
Turn the multimeter ON and set it to read voltage. Insert the black connector to the COM port and the red connector to the mVΩ port. Attach the red probe to the terminal that feeds the power and the black probe to the ground.
If the voltage reading across the breaker is either 120 or 220 volts, then it is working. If there is no voltage reading, then the breaker is bad and needs to be replaced.
In this module you learned about circuit breakers. A circuit breaker is a switching device that interrupts the power supply in a electrical circuit.
Question #1: Switches are used to make or break electric current in a circuit.
True
False
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Answer: True
Switches are used to complete or interrupt the flow of electric current in any circuit.
Question #2: What will be the current through a circuit when the switch is in the OFF state?
An Infinite value
0 Ampere
A finite value
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Answer: 0 Ampere
Whenever the switch is in the OFF state in any circuit, the current flowing through it will be zero.
Question #3: While testing the voltage of an SPST switch, the multimeter probes must be connected across the ______ terminal and the _____ terminal.
Hot, Ground
Hot, Neutral
Neutral, Ground
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Answer: Hot, Ground
An SPST switch has two hot terminals and a ground terminal. One probe must be connected to the hot terminal and the other to the ground terminal.
Question #4: For testing an SPST switch for resistance, the most crucial step is to disconnect it.
True
False
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Answer: True
For testing an SPST switch, it must be disconnected from the active power supply.
Question #5: For a functional switch in the off state, the multimeter must display a resistance value of ______.
OL or 1
10 Ω
100 Ω
1000 Ω
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Answer: OL or 1
In the off state, as the contact of the switch is not closed, an infinite resistance will be present. Therefore, the millimeter will display an OL (open-loop) or 1.
Question #6: How are contactors different from switches?
They are controlled manually
They are controlled electrically
These are un-controlled switches
None of the above
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Answer: They are controlled electrically
The contacts of the contactors are controlled electrically.
Most switches which are controlled mechanically.
Question #7: Contactors can handle current up to _______.
12.5 A
125 A
1,250 A
12,500 A
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Answer: 12,500 A
Contactors can usually handle a maximum current of about 12,500 A.
Question #8: For testing a contactor, the multimeter must be set to _____ setting.
Resistance
Voltage
Current
Capacitance
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Answer: Resistance
The working of a contactor can be checked by setting the multimeter to the resistance setting.
Question #9: What would be the resistance across the line and load terminals of a functional contactor in the OFF state?
A few ohms of resistance
An OL or 1
Any finite value in ohms
Zero
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Answer: An OL or 1
The OFF state of a contactor means the contactor contacts are not closed. An infinite resistance or an OL is observed since the contacts are not closed in the OFF state.
Question #10: What would be the resistance across the line and load terminals of a functional contactor in the ON state?
A few ohms of resistance
An OL or 1
Any finite value in ohms
Zero
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Answer: A few ohms of resistance
The ON state of a contactor means the contactor contacts are closed. Since the contacts are closed here, a finite resistance value close to zero is observed. However, the resistance must never be zero.
Question #11: The amount of heat generated in the resistance heating is given by the formula Q = I² ✕ R ✕ T. Here ‘I’ is ?
Inductance
Current
Voltage
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Answer: Current
The resistance heating is governed by the formula Q = I² ✕ R ✕ T. Here ‘I’ is the amount of current passing through the conductor.
Question #12: The amount of heat generated in the resistance heating is given by the formula Q = I² ✕ R ✕ T. Here ‘T’ is ?
Time
Current
Temperature
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Answer: Time
The resistance heating is governed by the formula Q = I² ✕ R ✕ T. Here ‘T’ is the amount of time for which the current passes through the conductor.
Question #13: What are the most crucial steps while inspecting a resistance heater?
Switch OFF the power supply
Switch ON the power supply
Cool the resistive heater
Heat the resistive heater
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Answer: Switch OFF the power supply
Cool the resistive heater
While inspecting a resistance heater, the two most crucial steps are switching OFF the power supply and cool the resistance heater.
Question #14: For a faulty resistance heater what would the multimeter display?
A few ohms of resistance
An OL or 1
Any finite value in ohms
Zero
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Answer: An OL or 1
If the resistance heater is faulty, it means that the element may be broken somewhere. Since the element is not continuous, the multimeter will display an OL (open-loop) or 1.
Question #15: The main function of an electric fuse is to interrupt the excessive _______.
Voltage
Current
Resistance
None of these
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Answer: Current
Fuses are used to interrupt the excess flow of current in a circuit. Fuses are used to protect the electrical equipment from over-current damages.
Question #16: The multimeter must be set to _ setting while inspecting a fuse:
Voltage
Continuity
Current
None of these
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Answer: Continuity
Remember that the multimeter must always be set to the continuity setting while inspecting a fuse.
Question #17: If the fuse wire inside a fuse is broken, what will the multimeter display?
An OL or 1
A few ohms of resistance
Any finite value in ohms
Zero
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Answer: An OL or 1
An OL reading will indicate the fuse to be faulty and a beep sound with a low resistance value will indicate the fuse to be functional.
Question #18: What is the primary function of a thermal overload switch?
Interrupts the excess flow of current
Prevents from damages of overheating.
Prevents from over-current
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Answer: Prevents from damages of overheating.
The function of a thermal overload switch is to prevent the electrical component from damages due to overheating.
Question #19: The thermal overload switch is connected in _____ connection with the power supply and the motor.
Series
Parallel
Series or Parallel
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Answer: Series
The thermal overload switch must always be connected in series configuration with the power supply and the electric motor.
Question #20: In the cold state, the multimeter reading across a working thermal overload switch must be ?
An OL or 1
A few ohms of resistance
Any finite value in ohms
Zero
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Answer: A few ohms of resistance
In the cold state, the terminal 1 and 2 of the thermal overload switch must be connected. Therefore, the multimeter will display a very low resistance reading.
Question #21: Whenever an excess amount of current flows in a circuit due to additional loads, this is said to be an overload.
True
False
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Answer: True
Every circuit is designed to handle a specified amount of load. If an excess current flows in a circuit due to additional loads, this is said to be an overload.
Question #22: An overload can be identified when a specific load is connected, breaker trips.
True
False
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Answer: True
If, on connecting a certain load in the circuit, the breaker trips, it indicates that there may be an overload.
Question #23: The working principle of a circuit breaker is similar to that of a ______.
Fuse
Contactor
Switch
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Answer: Switch
The basic working principle of a circuit breaker is just like a switch. It is responsible for turning the power supply in a circuit.