1. REPAIR FAULTS IN LOW VOLTAGE ELECTRICAL APPARATUS AND CIRCUITS
UEENEEG108
TROUBLE-SHOOT AND
REPAIR FAULTS IN LOW VOLTAGE
ELECTRICAL APPARATUS AND CIRCUITS
TOPIC 1 - FAULT FINDING

2. REPAIR FAULTS IN LOW VOLTAGE ELECTRICAL APPARATUS AND CIRCUITS
UEENEEG108
TROUBLE-SHOOT AND
REPAIR FAULTS IN LOW VOLTAGE
ELECTRICAL APPARATUS AND CIRCUITS
TOPIC 1
FAULT FINDING

3. TOPIC 1 - FAULT FINDING What is Fault Finding
Common Causes and Symptoms of Faults
Fault Finding Procedures

4. What is troubleshooting?
It is the process of analysing the behaviour or operation of a faulty circuit to determine what is wrong with the circuit.
It then involves identifying the defective component(s) and repairing the circuit.
Depending on the type of equipment, troubleshooting can be a very challenging task.

5. When Equipment Fails Urgency to get it fixed Downtime costs money
Loss of productivity
Costs involved with fixing equipment
Customers often watch you
Puts pressure on you to solve problem faster

6. List 5 steps you should undertake
before you start work on
a breakdown?

7. 1 Risk assessment
Isolation, working safely at heights, confined spaces, explosive gasses, poisonous gasses.. There are lots of potential hazards

8. 2 Ask
Find out exactly what the fault is and what were the circumstances that led to it.
Make your own assessment , don’t presume what you have been told is the whole truth, the operator may have made a mistake !

9. 3 Visual Inspection Check for jammed or seized machinery,
Look for cable damage.
Check fuses or circuit breakers
Check for tripped overloads or cut outs

10. 4 Use your senses
Have a look - some faults can be found simply by taking a look.
Listen - motors will hum if the start capacitor is faulty.
Smell - burnt cables or overloads will smell if heat damage has occurred.
Touch - feel the cables, are they hot?

11. 5 Test Use your test instruments to find the fault
Continuity of cables.
Insulation Resistance of cables.
Clamp meters, how much current is being drawn?
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12. Testing is considered to be “Electrical Work”
NO LIVE WORK!!
Testing is considered to be “Electrical Work”

14. Etc………..

15. Can you work on a switchboard (alone) if the main switch is turned off?
Main switch turned off

16. COMMON CAUSES OF FAULTS
Operator Faults
Defective wiring practices
Short Circuits
Open Circuits
Overloaded Circuits
Mechanical Faults
Supply Faults

17. 1. Operator Faults One of the most common faults.
Most of the time, the operator has failed to follow a procedure properly or something unexpected has happened.
Eg. Power is turned off

18. 2. Defective Wiring Practices
Loose connections.
Some insulation piercing connectors when applied incorrectly can make poor connections due to insufficient contact area or pressure.

19. 2. Defective Wiring Practices
Aluminum and copper conductors spliced together with an incorrect connector. Aluminum oxide causes overheating.
AS3000:2007 Clause
“Disimilar metals liable to initiate galvanic action shall not be placed in contact with each other”
“Materials liable to cause mutual or individual deterioration, or hazardous degredation, shall not be placed in contact with each other”
Eg. Cabling through polystyrene in portable buildings

20. 2. Defective Wiring Practices
Metal
Index (V)
Most Cathodic
Gold, solid and plated, Gold-platinum alloy
−0.00
Rhodium plated on silver-plated copper
−0.05
Silver, solid or plated; monel metal. High nickel-copper alloys
−0.15
Nickel, solid or plated, titanium an s alloys, Monel
−0.30
Copper, solid or plated; low brasses or bronzes; silver solder; German silvery high copper-nickel alloys; nickel-chromium alloys
−0.35
Brass and bronzes
−0.40
High brasses and bronzes
−0.45
18% chromium type corrosion-resistant steels (Stainless Steel)
−0.50
Chromium plated; tin plated; 12% chromium type corrosion-resistant steels
−0.60
Tin-plate; tin-lead solder
−0.65
Lead, solid or plated; high lead alloys
−0.70
2000 series wrought aluminum
−0.75
Iron, wrought, gray or malleable, plain carbon and low alloy steels
−0.85
Aluminum, wrought alloys other than 2000 series aluminum, cast alloys of the silicon type
−0.90
Aluminum, cast alloys other than silicon type, cadmium, plated and chromate
−0.95
Hot-dip-zinc plate; galvanized steel
−1.20
Zinc, wrought; zinc-base die-casting alloys; zinc plated
−1.25
Magnesium & magnesium-base alloys, cast or wrought
−1.75
Beryllium
−1.85
Most Anodic

21. 2. Defective Wiring Practices
Will only corrode if an “Electrolyte” is present.(Ie. Water). Like a battery….
Water

22. 2. Defective Wiring Practices
Cabling against sharp edges, causing cuts to insulation (particularly in ceilings – ie. Government Home Insulation Program)
Low-voltage applications (such as high-current landscape lighting) with field connections that are exposed to combustibles, such as woodchips, can be dangerous. Even though it’s low Voltage, high currents are involved. Poor connections can lead to fires.

23. 2. Defective Wiring Practices
Polarity
Incorrect polarity (ie. Crossed wires) will make the earthing system live.
Voltage test at the GPO will not show a fault
Voltage Test
Active to Earth = 230V
Active to Neutral = 230V
Neutral to Earth = 0V

24. 3. Short Circuits
A short circuit in an electrical circuit is one that allows a current to travel along a path where essentially no (or a very low) electrical impedance is encountered.
Can be between:
Active and Earth
Active and Neutral
Neutral and Earth

25. 3. Short Circuits
This results in an excessive electric current (overcurrent) limited only by the Impedance of the rest of the network and potentially causes circuit damage, overheating, fire or explosion.

26. Operation of Protective Device
3. Short Circuits
Typical Symptom:
Operation of Protective Device

27. 4. Open Circuits
The electrical opposite of a short circuit is an "open circuit", which is an infinite resistance between two nodes.
Can be caused by:
Broken cables
Mechanical Damage
Vibration
High resistance joints
Carbonised contacts
Galvanic action

28. Appliance/Device does not operate
4. Open Circuits
Typical Symptom:
Appliance/Device does not operate

29. 5. Overloaded Circuits
Overloaded circuits are when too much current flows through the circuit.
Can be caused by:
Too much load on motors
Too many appliances on a circuit
Undersized cables
Undersized electrical equipment (eg. Switches)
Oversized circuit breakers

30. 5. Overloaded Circuits HEAT
The outcome of an overloaded device or circuit is
This can lead to:
Breakdown of insulation
Damage to electrical devices
Short circuits
Fires
HEAT

31. 5. Overloaded Circuits Operation of Protective Device Typical Symptom:
(same as Short Circuit)

32. 6. Mechanical Faults
Non-Electrical (mechanical) faults can often lead to electrical faults
Overloaded motors
Broken parts
External damage

33. 7. Supply Faults Blackouts Loss of Supply Brownouts
Reduction in Supply Voltage
Causes lights to dim
Can cause damage to circuits
V=IR
Decrease in Voltage causes Increase in Current
Loss of Phase
3 phase systems
Can cause motor damage (overload)
Under Voltage
Over Voltage

34. Wet Arc Tracking
Initially caused by moisture/ conductive material build-up between terminals or plug pins
Forms a path/bridge for current to flow (not enough to trip circuit)
Starts out as a very high resistance path, but over time, carbon build up forms a “track” for current to flow
Current flow causes heat, which can eventually cause fires
Eg. Salt water on aquarium electrical devices or the rinse aid in a dishwasher leaking onto internal wiring.

35. Dry Arc Tracking Usually caused by overloading and poor connections
Insulation overheats and plastic degrades
Turns plastic from hydrocarbon into elemental carbon (which is a semi-conductor)

36. Insulation Breakdown Can be caused by: Overloading
Mechanical damage (immediate or over time)
Insulation can become brittle if cable is overloaded for long periods
Also, some cables are not UV stabilised.
Insulation can breakdown and cause short circuits

37. How do we improve Electrical Safety?
Install RCD’s on all circuits
Install electrical equipment that is suitable for the environment it is in. (eg IP ratings)
Mechanical protection (cables and electrical equipment)
Avoid poor wiring practices
Cable sizing
Connections
Protection
Equipment ratings

38. Circuit Protection Circuit breakers protect against Over-current
Short Circuits
If they are sized correctly
Over-current Trip Curve
B-Curve – 4 times
C-Curve – 7.5 times
D-Curve – 12 times

39. Circuit Protection Residual Current Devices (RCD) protect against
Earth Faults
RCD only
Combined RCD + MCB
(RCBO)

40. FAULT FINDING PROCEDURES
Talk to Client/Operator
Observe
Define Problem Area
Identify Possible Causes
Determine Most Probable Cause
Test and Repair
Follow Up

41. Fault Finding Procedure
1. Talk to Client/Operator
The first report of a fault is going to come from a customer/operator.
It is most important at this stage to get as much information on the fault as possible.
What you are told at this stage may indicate what the fault is and what tools, equipment and spare parts you might require

42. Fault Finding Procedure
2. Observe
Most faults provide clues as to their cause. There could be visual clues such as signs of damage or improper operation.
Don’t forget to use your other senses; sounds and smells can also provide valuable clues.
Through careful observation and a some reasoning, most faults can be identified to the actual component with very little testing

43. Fault Finding Procedure
2. Observe (cont’)
Be sure you understand how the equipment is designed to operate. It makes it much easier to analyze faulty operation when you know how it should operate;
Note the condition of the equipment as found.
You should look at the state of the relays (energized or not),
Which lamps are lit,
Which auxiliary equipment is energized or running etc.

44. Fault Finding Procedure
3. Define Problem Area
At this stage you apply logic and reasoning to your observations to determine the problem area of the malfunctioning equipment.
Understand the circuit and how it operates
Use Circuit Diagrams, Plans or Operation Manuals to help determine:
How the equipment or circuits should operate
What kind of features the circuit has
What voltages you should expect at various points on the circuit
Where components are physically located
How the components are actually wired together
Draw a circuit diagram if one isn’t available

45. Fault Finding Procedure
4. Identify Possible Causes
Once you have the problem area(s) defined it is necessary to identify all the possible causes of the malfunction.
Sometimes it is possible that there are 2 or more faults in a circuit. One fault may lead to another fault developing

46. Fault Finding Procedure
4. Identify Possible Causes (cont’)
Make a list of all possible causes in order of likelihood
First look for components which burn out or have a tendency to wear out, i.e. mechanical switches, fuses , relay contacts, or light bulbs. (Remember, that in the case of fuses, they burn out for a reason. You should find out why before replacing them.)
The next most likely cause of failure are coils, motors, transformers and other devices with windings. These usually generate heat and, with time, can malfunction.

47. Fault Finding Procedure
4. Identify Possible Causes (cont’)
Connections should be your next choice, especially screw type or bolted type. Over time these can loosen and cause a high resistance. In some cases this resistance will cause overheating and eventually will burn open. Connections on equipment that is subject to vibration are especially prone to coming loose.
Finally, you should look for is defective wiring. Pay particular attention to areas where the wire insulation could be damaged causing short circuits. Don't rule out incorrect wiring, especially on a new piece of equipment.

48. Fault Finding Procedure
5. Determine Most Probable Cause
Once the list of possible causes has been made it is necessary to prioritize the items as to the possibility of them being the actual cause of the malfunction.
6. Test and Repair
Once you have determined the most probable cause, you must test it to prove it to be the problem or not.
Always try to predict what your measurement should be before you test

49. Fault Finding Procedure
6. Test and Repair (cont’)
After replacing the component, you must test operate all features of the circuit to be sure you have replaced the proper component and that there are no other faults in the circuit.
It can be very embarrassing to tell the customer that you have repaired the problem only to have him find another problem with the equipment just after you leave.
Document any changes that have been made

50. Methods for Testing Assumptions
Visual Inspection
Component Isolation
Eg. If an RCD is tripping, First unplug all appliances and then plug back in one at a time.
Test Equipment
Use multimeter or other instruments to test if equipment is faulty
Sectional Testing
Test one section at a time
Split-Half Tests
Split the circuit up and test each half to isolate the problem
Repeat as required until fault is found

51. Test Equipment
The most common test equipment used by electricians is a multimeter and a insulation resistance tester (megger).
Multimeter
A multimeter as its name implies has more than one function. It will usually have a volt meter, an amp meter and an ohm meter.
It may also contain other functions such as capacitance testing, temperature testing, decibels and many more.
Careful selection of a multimeter which has all the functions you may require in your particular line of work.

52. Test Equipment Insulation Resistance Tester (Megger)
This meter is used to measure ohms and differs to the ohm meter (in a multimeter) in that it measures in much higher numbers (ie. megga ohms)
Also uses a much higher voltage to do the test,
Normally 500volts d.c. for single phase and
1000v d.c. for 3 phase testing.
Can have analogue or digital displays

53. Test Equipment
There are 4 different categories of meters, category 1 having the lowest protection level and category 4 having the highest.
Category 3 is suitable for most electrical work unless working on High Voltage distribution systems where category 4 is the most suitable.

54. Test Equipment Testing Safely
Testing should be carried out only on an isolated circuit unless there is no other option.
Obviously if you have to test if the correct voltage is present it can only be ascertained by testing live.
Any disconnections or changes made to the circuit must be re- instated before returning power to the circuit.
Care should be taken when testing for power that the “hold” button has not been accidentally activated as this will give false readings. Eg. It may read zero volts when there is power present.

55. Fault Finding Procedure
7. Follow up
A follow up call should be made once the equipment has been repaired and put back in service to ensure that the problem has been repaired properly.

56. Intermittent Faults The hardest faults to find
Normally need the fault to occur while you are watching
Typical Causes
Vibration
Loose connections
Shock (causing items to operate un-intentionally)
Changes in temperature
Electromagnetic interference

57. Intermittent Faults How to resolve intermittent faults
Make changes to the environment that may be causing the problem
Temperature/Humidity (install a controlled environment ie. Air Conditioning)
Vibration
Replace the part you believe is causing the problem (with permission from customer/owner)
Leave it running and see if fault happens again (only if the fault will not cause a dangerous situation)