Cables & cords
What colour can an earth conductor be?
Green
Green/Yellow
Give three examples of how an arc flash can occur
Broken conductor
Poor termination or crimp
Mice/rats touching across conductors
Earthed equipment contacting live conductors
Opening switches or contacts under load
Explain the connection points on an Edison screw fitting?
Phase must be at the base, neutral on the side
Describe an open circuit?
An open circuit is where a circuit becomes broken, and can no longer complete a circuit for current to flow
In which section of AS/NZS3000 would you find testing?
Section 8
DOUBLE POINTS!!
What colour are the cores in multi-phase flexible cables?
Double for current NZ & European colours
L1 Red Brown
L2 White Black
L3 Blue Grey
N Black Blue
E Green/Yellow
What factors make up impedance?
Capacitance
Inductance
Resistance
What is written on an earth tag?
"Main earthing conductor - DO NOT DISCONNECT"
What is a danger of solar (PV) panels?
If there is light on the panel, they are producing an output voltage
What is the maximum permitted main earth resistance value?
0.5Ω
Explain the insulation on a Thermoplastic sheathed cable
PVC cores beside each other, with an outer sheath of PVC over the top
ITS A ROBBERY!!
Name the operating times and current for both types of RCD
Type 1 (Kindergarten, Electromedical)
10mA, 40ms
Type 2 (Domestic)
30mA, 300ms
What does IP rating mean?
DOUBLE POINTS, if you can explain the code
Ingress Protection (IP) rating
The first digit is how well the fitting will keep out solid objects. The second number is how well the fitting will keep out water and liquids
What is the purpose of testing for earth fault loop impedance?
To confirm by testing that the earth loop has a low enough impedance to cause a large amount of current to flow in the event of an earth fault, which causes the protective device to operate quickly
What is the maximum permitted appliance resistance value?
1Ω
In a fire rated 3c and earth cable what is the difference in the cores to a standard cable?
Mica glass core protecting tape
Explain an earth leakage fault
A small amount of current leaking out of the circuit and not returning via the neutral as it should
Current leakage measured typically in milliamps
ITS A ROBBERY!!!
Name at least three options for fire rating
Fire rated gib
Metal flush boxes with heat pads
Fire collars
Fire sealant
Describe a circuit with an overload?
The circuit is operating correctly, but has too many loads attached to it. An overload may not even be caused by an electrical fault, it may just be user error.
ITS A ROBBERY!!!
In a circuit how would you connect an ammeter and how would you connect a voltmeter?
Voltmeter connected in parallel
Ammeter connected in series
When a cable is marked with V90 2.5 mm² 450/750V, what does this mean for the conductors rating?
The cable is rated to run at 75°C with an absolute maximum temperature of 90°C
DOUBLE POINTS!!
Explain how a a clip on ammeter works?
They are put around the current carrying conductor and are used to measure the magnetic field that is produced by the current.
Only one core at a time as two will cancel each other out
What are the hazards of drilling into fibre cement board?
What should you do to minimise these?
Cancer
Loss of lung function
Wear a P2 dust mask
What can cause an over voltage?
Undersized conductors that are not big enough to carry the circuit current
Bad connection in the circuit causing high impedance
What is the cable insulation resistance value for a MIMS cable?
0.01MΩ
10,000Ω