I 🙅 numbers
What is the parallel resistor equation?
Rt = (R1-1+R2-1)-1
How do you reverse the direction of a single phase motor?
Change one set of windings only
Name three core shapes
Core
Shell or E
Torodial
What is the minimum insulation resistance result?
1MΩ
ITS A ROBBERY!!
When isolating a circuit you must do your mandatory tests, where would you find these, & in which standard?
AS/NZS3000:2007
Section 8
Where must the phase be located in an Edison screw light fitting?
In the centre of the fitting
What is the purpose of adding a capacitor to a start winding?
It increases starting torque
What is the turns ratio of an isolating transformer?
1 : 1
What is the maximum appliance earth value?
1Ω
Explain prove - test - prove
Prove you meter is working on a known live source
Test the equipment that you want isolated
Re-prove your meter is working on a known live source
What are the trigonomic functions
DOUBLE POINTS
Draw them on the whiteboard
sin θ opp/hyp
cos θ adj/hyp
tan θ opp/adj
Explain the difference between start and run windings?
Start winding has smaller gauge wire & fewer turns
Run winding has heavy gauge wire & many turns
What is the rating of a transformer given as?
VA
kVA
MVA
The resistance of the main earth conductor shall not be more than?
0.5Ω
What is the purpose of shutting down equipment/ removing the load when isolating?
To prevent arcing
To stop unexpected start ups of machinery
What are the Pythagoras formulas?
C2 = A2 +B2
A2 = C2 - B2
B2 = C2 - A2
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How & why does the centrifugal switch disengage?
The switch has hinged weights held in by springs which disengage at 75% speed.
This disconnects the start winding and leaves the run winding to provide power to the motor.
What is the turns ratio between primary and secondary windings?
Primary Secondary
Many turns Few turns
High Voltage Low voltage
Low current High current
DOUBLE POINTS!!
Name the type & operating times for RCDs
Type 1
10mA 40ms
Type 2
30mA 300ms
There are three categories of work to be certified
DOUBLE POINTS IF YOU CAN NAME THE CERTIFICATION NEEDED
Low risk - ESC
General work - ESC & COC
High risk work - ESC, COC & ROI
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What is the volt drop equation for single phase?
Vd = L x I x mv/a/m
1000 x 1.155
DOUBLE POINTS!!
Draw a motor on the board and label at least 4 components
Case/frame Fan
Stator core & windings Shaft
Rotor Capacitor
Terminal box Bearings
What is the transformer calculation?
DOUBLE POINTS!!
What does each part of the equation mean?
Np = Vp = Is
Ns Vs Ip
# of turns - Primary & secondary
Voltage - Primary & secondary
Current - Primary & secondary
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What is an acceptable earth value for a MIMS element?
0.01MΩ
10kΩ
10,000Ω
Which 3 standards could you use for testing portable appliances?
DOUBLE POINTS IF YOU CAN NAME THEM
AS/NZS3760 - In-service safety inspection and testing of electrical equipment
AS/NZS5761 - Second-hand equipment prior to sale
AS/NZS5762 - Repaired equipment