UEE31307 Certificate III in Refrigeration and Air Conditioning

Stage 2A Units: UEENEEPOO2B

Chris Hungerford4/10/23

EKAS 2.19.36

Fault find- General Appliances

The two golden rules• Test before you touch, this

protects you physically, so you can have a good day!

• Test your work is electrically safe when completed, tests include insulation resistance, earth continuity, polarity, and visual inspection, this protects you financially.

2.19.36.A

Safe Isolation of a Supply

• Test before you touch, this protects you physically, so you can have a good day!

Procedure to isolate a Supply1. Notify all persons likely to be affected by the isolation.2. Determine the method to isolating the supply.3. Test the supply availability.4. Isolate the supply.5. Danger tag the isolation device.6. Test that the supply is isolated.7. Test the testing device.

2.19.36.A

Are you working LIVE?Using a voltmeter to measure low voltage is working live!

Electrical Safety Regulation 200211 Requirements for electrical work(1) An employer or self-employed person must ensure that, unless the circumstances required under this division for the performance of live work apply, live work is not performed.Maximum penalty—40 penalty units.

WARNING

As per Regulation 12 “Requirement for performance of live work”, to perform live work you must satisfy the following seven (7) questions:

1. Have you prepared a risk assessment?2. Is your test equipment appropriate to perform live work? Minimum Cat III @ 500v ac.

3. Has your test equipment been maintained and confirmed that it is operating correctly? Regulation 18.2(b) “the instrument is tested at least every 6 mths to ensure it is in proper working order”, and Regulation 12.1(f) “the instrument is tested immediately prior to work to confirm that the instrument is operating correctly”

4. Have you the correct PPE, (Safety boots, long pants, long sleeved shirt, insulated gloves, safety glasses)? As per AS/NZS 4836 Safe working on low voltage electrical installations.

5. Is the isolation point clearly identified?6. Is the isolation point able to be reached without any obstructions?7. Is the area where the electrical live work is performed clear of any obstructions?Note: if you are not working within the requirements of the above laws then your inaction to comply threatens the following; 1. Your right to claim workcover in the event of an accident2. Your right to claim any insurance benefits in the event of an accident3. You will be fined the prescribed penalty units for those laws that you have breached.2.19.36.A

CAT IV-600 V CAT III-1000 V

What’s the bottom line?• If you work on power circuits, you

need a CAT III-600 V or CAT IV-600 V/ CAT III 1000 V meter.

• Look for the CAT rating and voltage rating marked near the input jacks.– CAT or voltage rating alone can be

misleading

• Look for independent certification.

2.19.36.A

Heaters & heating devices

• All heating devices are resistive, therefore:– Current can be calculated using the power rule.– Resistance can be calculated using Ohm’s Law.

Determine the current & resistance of this12kW 240V Duct heater.

I = P/V = 12000/240 = 50A

R= V2/P = (240 x240) / 12000 = 4.8

2.19.36.B

Volts Current

240v 24

604A

100v

48

3.6kW

1.2kW

Resistance Power

250W5A

Determine the unknown values of the heating elements

2.19.36.B

Volts Current

240v 24

604A

100v

48

3.6kW

1.2kW

Resistance Power

250W5A

10A

36A

5A

240v

240v

50v 10

2.7

2.4kW

960W

Answers

2.19.36.B

Temperature control.AS/NZS 3000:20074.11 ELECTRIC DUCT HEATERSThe electrical portion of any electric duct heater installation shall comply with the

requirements of this Standard.NOTE: Attention is drawn to the fact that—(a) such installations are within the scope of AS/NZS 1668.1; and(b) safety requirements are contained in AS/NZS 3102; and(c) compliance therewith may be required by the relevant regulatory authorities.

2.19.36.B

AS/NZS 3102:20027 PROTECTION AGAINST HEAT AND FIRE7.1 Fixing of heating unitsAn electric heating unit incorporated in a duct heater shall be assembled and firmly supported so

that it will not introduce a risk of fire through displacement resulting from loosening of fixings or other defects likely to be brought about by vibration or other conditions of service.

7.2 Interlocking of supply to heater unit and blower motorThe electrical supply to the heating unit(s) shall be interlocked with the supply to the associated

blower motor such that interruption of supply to the blower motor will automatically interrupt supply to the heating units.

7.3 Devices to prevent overheatingThe duct heater shall be provided with both the following devices as a safeguard against

overheating under abnormal operating conditions:a) A device to interrupt electric supply to the heating unit if airflow through the duct heater ceases.

This device may be a thermal cutout or an air supply failure switch. The device shall comply with the test requirements of Clause 17.8.2.

b) A non-self-resetting thermal cutout, located within the duct heater casing or air duct adjacent to the heating units, so that the air temperature in the immediate vicinity of the heating units does not exceed 120°C under abnormal operation. The thermal cutout shall comply with the test requirements of Clauses 17.8.1 and 17.8.2.

NOTE “immediate vicinity” is considered to be a distance of 25 mm. The devices mentioned in a) and b) may interrupt the heating unit current directly or they may form part of a system in which they interrupt the heating unit current indirectly via a component such as a contactor. The device or system providing protection during abnormal operation shall not operate during normal operation.

The devices or systems are not required if the air temperature in the immediate vicinity of the heating units does not exceed 120°C under the abnormal operation conditions described with the devices short-circuited.

2.19.36.B

Thermostat Fluid operated bellows. These are not that common in small appliances but often found in refrigerators, air conditioners, domestic ovens, and so forth. An expanding fluid (alcohol is common) operates a bellows which is coupled to a set of movable contacts.

2.19.36.B

Expanding Tube thermostatExpanding Tube thermostat

Thermostat

2.19.36.B

Oven

Ele

men

t

Thermostat

A

N

Thermostats are closed Loop control

Liquid Filled

BellowsElectricalContacts

2.19.36.B

Liquid Filled Thermostat

2.19.36.B

ThermostatElectronic thermostats. These typically use a temperature controlled resistance (thermistor) driving some kind of amplifier or logic circuit which then controls a thyristor or contactor.

2.19.36.B

Thermostat NTC Thermistors:•Are non-linear•Change resistance dramatically with temperature (they have a very high sensitivity)•Are not interchangeable•Are not suited to wide spans•Suffer from drift and decalibration at high temperatures•If the resistance of a thermistor is 5,000Ω at room temp, it may drop to about 20Ω at 300C and rise to about 200,000Ω at -50C.

TEMPERATURE °C

RE

SIS

TA

NC

E (

Ohm

s)

200K

100K

20k

0

0 200100 300-100

40k

2.19.36.B

Other temperature measuring devices

• Thermocouples

• Resistance Temperature Detectors(RTD’s)

• Diodes and semiconductor IC’s

• Gas expansion system

• Mercury expansion system

• Coiled bimetal strip

• Radiation Pyrometers

2.19.36.B

Thermostat settingsDifferential

Time

Tem

pera

ture

20°C

DifferentialSetPoint

It is the difference between the turn-on temperature and the turn-off temperature of the thermostat.

2.19.36.B

Simmerstat controlThe simmerstat consists of a parallel

connected heater that causes a bi-metallic switch to bend and open circuit.

Load

N

Line

Load

Problems; No control, open circuit heater or welded switch contact. No output, damaged switch contacts.

2.19.36.B

Energy cut-outs

• They are not adjustable.

• Designed to cut off the supply before the appliance damages itself due to a failure of the thermostat.

2.19.36.B

Fault finding heating circuits

A N NA 240V

thermal cutout

Blowerinterlock

Thermostat24kw heater

Voltmeter = 240v

Fuse

Client: Hello…..Heater does not operate!Step 1. Test supply is available at heater terminals and element.Caution: Working live….. All work as per regulation 12.

A

Voltmeter = 240v

Switchboard

Field (on heater)

2.19.36.B

Fault finding heating circuits

A N NA 240V

thermal cutout

Blowerinterlock

Thermostat24kw heaterFuse

Ask yourself, “I have supply at the element, this heater should operate”?Step 2. Isolate the supply and test to confirm isolation, tag, ……..supply isolated.Step 3. Measure the resistance of the element, compare the value to your determined value using ohm’s law.

isolate

R= V2/P = (240 x240) / 24000 = 2.4

Ohmmeter = 20M

2.19.36.B

Fault finding heating circuits

A N NA 240V

thermal cutout

Blowerinterlock

Thermostat24kw heaterFuse

Ohmmeter = 20M

R= V2/P = (240 x240) / 24000 = 2.4

These two values should be approximately equal

Remember; Very high values of resistance = open circuit. Very low values of resistance = short circuit.

Therefore the fault with this circuit is an open circuit element.

2.19.36.B

Fault finding heating circuits

A N NA 240V

thermal cutout

Blowerinterlock

Thermostat24kw heaterFuse

Client: Hello…..Heater does not operate!Step 1. Test supply is available at heater terminals and element.Caution: Working live….. All work as per regulation 12.

Voltmeter = 0v

A

2.19.36.B

Fault finding heating circuits

A N NA 240V

thermal cutout

Blowerinterlock

Thermostat24kw heaterFuse

No supply available at heater!Step 1. Check supply at switchboard.Step 2. Check condition of fuse or circuit breaker.

E

Voltmeter = 240vOhmmeter = 20M

High resistance = open circuited fuseThis fuse has blow for a reason, do not

replace it until the reason for blowing has been determined.

2.19.36.B

Fault finding heating circuits

A N NA 240V

thermal cutout

Blowerinterlock

Thermostat24kw heaterFuse

Reasons for a Fuse to blow1. An overload.2. A Short circuit.3. A partial short circuit.

1. An overload.Step 1. measure the resistance of the circuit.Step 2. determine the current from the measured values.Step 3. compare determined current to the size of the fuse.

Ohmmeter = 1.5 I = V/R = 240/1.5 =160A.

120A

The calculated value should be

less than the fuse rating.

2.19.36.B

Fault finding heating circuits

A N NA 240V

thermal cutout

Blowerinterlock

Thermostat24kw heaterFuse

120A

2. A Short circuit.Step 1. Measure the resistance of the circuit.

Ohmmeter = 0.005

Step 2. Break the circuit at the element and measure it’s resistance.the ohmmeter scale should be set to the x1 scale.

2.19.36.B

Fault finding heating circuits

A N NA 240V

thermal cutout

Blowerinterlock

Thermostat24kw heaterFuse

Step 2. Break the circuit at the element and measure it’s resistance.

120A

Ohmmeter = 0.005

The correct value of element resistance = 2.4.The measured value is very low therefore the fault is a short circuit, look for loose or damaged wiring, or replace the element.

R= V2/P = (240 x240) / 24000 = 2.4

2.19.36.B

Fault finding heating circuits

A N NA 240V

thermal cutout

Blowerinterlock

Thermostat24kw heaterFuse

3. A Partial Short circuit

This type of fault is commonly a leakage to earth fault.-The fuse may or may not be blown, Safety switches will trip.-The client may report shock tingles from the equipment.

E

Step 1. Isolate the supply and test to confirm isolation, tag, ……..supply isolated.Step 2. Perform an insulation resistance test on the whole circuit between all active conductor to earth. AS/NZS 3000 minimum value > 1MThe meghommeter scale should be set to 500vDC

Megohmmeter = 500

Here the megohmmeter indicates a leakage to earth,But which component of the circuit is faulty?Step 3. Break the circuit in ½ and test each side.

120A

2.19.36.B

Fault finding heating circuits

A N NA 240V

thermal cutout

Blowerinterlock

Thermostat24kw heaterFuse

120A

E

Megohmmeter = 120MStep 3. Break the circuit in ½ and test each side.

E

Megohmmeter = 500

The insulation resistance of the heating element is> 1M, therefore is good. The reading on the thermostat side of the circuit is < 1M, therefore faulty.

Step 4. Break the faulty circuit in ½ and test each side.

2.19.36.B

A N NA 240V

thermal cutout

Blowerinterlock

Thermostat24kw heaterFuse

120A

EE

Megohmmeter = 120M

Fault finding heating circuits

Megohmmeter = 500

Step 4. Break the faulty circuit in ½ and test each side.

The blower interlock circuit is less than 1M Therefore the fault is within that area of the circuit.

2.19.36.B

Electric Motors

The electric motor is an inductive device, ie, it has coils of wire and principle operation is due to the magnetic effect.

2.19.36.B

The StatorIron core

Copper winding Mounting frame2.19.36.B

The rotorThe rotor earns the name being the

moving part of the motor.

The rotor bars induce a current that sets up a magnetic field that opposes the original magnetic field, thus, set up a magnetic repulsion-attraction action.

Rotor bars

Cooling fan

2.19.36.B

Testing motor windings

• Check the resistance of the motor windings to determine if a fault has occurred.

• On single phase motors measure: start to common winding, run to common winding, and start to run winding.

• Check phase to ground. –Ohms reading between

S-R should be the total of both R & S winding.

–High insulation resistance between any winding conductor to ground

Typical resistance test on a 1 motor

2.19.36.B

Testing motors on the bench• Continuity of winding• Resistance of windings• Insulation resistance • At least 1MΩ• Mechanical check• Can it turn• Visual check• Vents, end shields, balance weights in place, key

not dangerous

2.19.36.B

A N NA 240V

240v 25WLamp

240v 100WEvaporator fan

Door switch

E

Thermostat

Run

Start

Thermaloverload

CurrentRelay

Compressor

Small domestic refrigerator

Issue: Refrigerator does not operate! Refrigerator does not make any sounds!

Step 1. Remove plug top from socket outlet.Step2. Using your voltmeter test socket outlet for a supply

Supply indicates 240V, therefore the fault maybe with the appliance.

2.19.36.B

A N NA 240V

240v 25WLamp

240v 100WEvaporator fan

Door switch

E

Thermostat

Run

Start

Thermaloverload

CurrentRelay

Small domestic refrigerator

Issue: Refrigerator does not operate! Refrigerator does not make any sounds!

Step 3. Place an ohmmeter across the A & N pins on the plug top.Step 4. Think..! At this point of time what should be operating within this refrigerator?

The evaporator fan and the compressor. Now determine what value of resistance should the ohmmeter be indicating.Compressor approx 20, evap fan approx 80 = total resistance approx 16

Ohmmeter = 15M

The ohmmeter indicates a high value of resistance therefore = open circuit, but where?

2.19.36.B

A N NA 240V

240v 25WLamp

240v 100WEvaporator fan

Door switch

E

Thermostat

Run

Start

Thermaloverload

CurrentRelay

Compressor

Small domestic refrigerator

Step 5. Remove compressor terminal cover and connect an ohmmeter between the neutral pin of plugtop and circuit wiring.

Ohmmeter = 0.5Good reading

Ohmmeter = 20Good reading

2.19.36.B

A N NA 240V

240v 25WLamp

240v 100WEvaporator fan

Door switch

E

Thermostat

Run

Start

Thermaloverload

CurrentRelay

Compressor

Small domestic refrigerator

Step 6. Remove thermostat cover.Attach an ohmmeter between A pin of plugtop and circuit

Ohmmeter = 15MBad reading!

Fault identified as an open circuit of the Active conductor2.19.36.B

Final Tests1 Visual inspection, is the work as per AS/NZS-3760?

2 Earth continuity test, is the earthing circuit continuous? AS/NZS-3760: < 1.

3 Insulation resistance test, is the conductors insulation able to contain the operating voltage?

AS/NZS-3760 2003 > 1M4 Polarity, are the outlets correctly connected, are the

circuit actives switched?

2.19.36.C

A N NA 240V

240v 25WLamp

240v 100WEvaporator fan

Door switch

E

Thermostat

Run

Start

Thermaloverload

CurrentRelay

Compressor

Small domestic refrigerator

Don’t forget to perform your safety tests on the appliance!1. Visual inspection.2. Earth continuity. One connection on the earth pin

The other on the metal frame.

AS/NZS3760

< 1

2.19.36.C

A N NA 240V

240v 25WLamp

240v 100WEvaporator fan

Door switch

E

Thermostat

Run

Start

Thermaloverload

CurrentRelay

Compressor

Small domestic refrigerator

Don’t forget to perform your safety tests on the appliance!1. Visual inspection.2. Earth continuity.3. Insulation resistance test

AS/NZS 3760

> 1M

2.19.36.C

Work Record required by Regulations

Electrical Safety Regulation 2002Part 2 Electrical work

14 Testing of electrical equipment after electrical work

(1) This section applies if electrical work is performed on electrical equipment.

(2) A person who performs part or all of the electrical work, and is responsible for bringing the electrical equipment to a state of readiness for connection to a source of electricity for use for its intended purpose, must ensure the electrical equipment is tested, as required under subsections (5) and (6).

Maximum penalty—40 penalty units.

.

2.19.36.C

Date of inspection

Appliance Visual inspection

Earth continuity

Insulation resistance

M

Polarity = Correct

RCD test current

30 MA trip timeMilliseconds

0 180 Test butt

2/7/09 Refrigerator ( LG model R100020 Serial 1004039832)

O.K 0.3 75M N/A N/A N/A N/A

2/7/09 Safetypac (Clipsal mod 56B, serial 9987987)

o.K. 0.8 187M 22 18

Electrical Safety Regulation 2002 Part 2 Electrical work15 Certificate of testing and safetyThis section applies if a licensed electrical contractor performs electrical work that must be tested

under this division.(2) The contractor must, as soon as practicable after the testing, ensure that the person for whom the

electrical work was performed is given a certificate complying with this section.(5) A licensed electrical contractor must keep a copy of a certificate given under this section for at least

5 years after the certificate is given.Maximum penalty for subsection (5)—20 penalty units

Work Record required by Regulations

Certificate of Testing and SafetyAs per Electricity Safety Regulation 2002,Part 8”Electricity Supply”, Division 2 “Testing”, Regulation 15,”Certificate of Testing & Work”

Electrical worker who tested the electrical work.

Phone Licence No: Contractors Licence Details of work

Details of Electrical Contractor Inspection Certificate No:

Acts, Regulations,Codes of Practices & Standards.

Electricity Act 1994 & Electricity Regulation 2006Electrical Safety Act 2002 & Electrical Safety Regulation 2002AS/NZS 3000:2000. Incorporating Amendment No. 1 (September 2001), Amendment No. 2 (April 2002), & Amendment No. 3 (July 2003). The Wiring Rules.

AS/NZS 3008.1.1:1998, Electrical installations— Selection of cables Part 1.1: Cables for alternating voltages up to and including 0.6/1 kV—Typical Australian installation conditions

I certify that the electrical installation work listed above has been tested in accordance with the prescribed procedures and that such work is electrically safe and complies in every respect with the requirement of the Electricity Safety Regulation 2002, regulation 159.Signature of Electrical worker:

Date of Certification:

2.19.36.C

Manufacturer Specifications of disconnected & replacement equipment.

When replacing any load you should be sure that the new item is suitable with regards to: Speed, Rotation, Power rating, Voltage, Current, Physical size, Environmental conditions & design of replacement, Dust & waterproof, temperature, UV rating, touch proof, life span.

2.19.36.C

Energising supply• Only after the visual inspections and safety testing as per

AS/NZS 3000:2007 has proven that the circuit is fit for purpose are you to energise the circuit.

• Remove only your Danger tag. If another worker has their danger tag on the isolated point then you can not energise.

• If clear: Energise the circuit.• Test for the correct and safe operation of the circuit, i.e.

rotation, system performance, current draw, voltage, etc.• Prepare all your safety and performance documentation.

2.19.36.C

Further reading: Textbook

Questions: Workbook, Topic 5, Q1 – Q10