Section 8

I 🙅 numbers

100

What is the parallel resistor equation?

Rt = (R1^-1+R2^-1)^-1

200

Where must the phase be located in an Edison screw light fitting? 

In the centre of the fitting

300

What are the trigonomic functions

DOUBLE POINTS

Draw them on the whiteboard

sin θ opp/hyp

cos θ adj/hyp

tan θ opp/adj 

400

What are the Pythagoras formulas? 

C² = A² +B²

A² = C² - B²

B² = C² - A²

500

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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

Motors

100

How do you reverse the direction of a single phase motor?

Change one set of windings only

200

What is the purpose of adding a capacitor to a start winding?

It increases starting torque

300

Explain the difference between start and run windings?

Start winding has smaller gauge wire & fewer turns

Run winding has heavy gauge wire & many turns

400

ITS A ROBBERY!!

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.

500

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

Transformers

100

Name three core shapes

Core

Shell or E

Torodial

200

What is the turns ratio of an isolating transformer?

1 : 1

300

What is the rating of a transformer given as?

VA

kVA

MVA

400

What is the turns ratio between primary and secondary windings?

Primary                          Secondary

Many turns                     Few turns

High Voltage                   Low voltage

Low current                    High current

500

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

I ❤️numbers

100

What is the minimum insulation resistance result?

1MΩ

200

What is the maximum appliance earth value?

1Ω 

300

The resistance of the main earth conductor shall not be more than?

0.5Ω 

400

DOUBLE POINTS!!

Name the type & operating times for RCDs

Type 1

10mA        40ms

Type 2

30mA        300ms

500

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What is an acceptable earth value for a MIMS element?

0.01MΩ 

10kΩ 

10,000Ω 

Isolation

100

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

200

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

300

What is the purpose of shutting down equipment/ removing the load when isolating?

To prevent arcing

To stop unexpected start ups of machinery 

400

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

500

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