Electrical Capstone - 2023

Why are inductors sometimes used to control current in an A.C circuit, rather than resistors?

Inductors have close to 0 power loss.

What is the RMS value of a current/voltage equal to?

the d.c. current/voltage that dissipates the same amount of power as the average power dissipated by the alternating current/voltage.

A watt meter connected to measure power in a single phase ac circuit indicates the:

Avg. power

The two factors that determine the frequency of the three phase supply from an alternator are:

Rotation speed and number of poles

The value of line voltage which is used on appliance rating plates for an a.c. supply is the:

RMS Value

A maximum demand indicator measures the maximum:

Current drawn from a supply

What does the neutral current of a balanced three phase star load equal?

0A

In an a.c. circuit containing resistance and inductance in series, the phase angle will be increased if the:

Frequency is increased

In a star connected load, Phase Current is equal to:

Line Current

In a star connected load, Line Voltage is equal to:

√3*Phase Voltage

In a delta connected load, Line voltage is equal to:

Phase Voltage

In a delta connected load, Line Current is equal to:

√3*Phase Current

In a star connected load, Phase Voltage is equal to:

Line Voltage/√3

In a delta connected load, Phase current is equal to:

Line current/√3

What type circuit breaker should be used to minimise the risk of inadvertent tripping due to motor starting currents

A type D breaker

What is the maximum rating of a three-phase induction motor that is not required to have over-temperature protection, and only operates when someone is present? (AS3000: 4.13.3.1)

2250W

When selecting an isolating switch for an AC motor and the motor manufacturer has not provided any specific information as to the starting current, the locked rotor or stall current shall be taken as (AS3000: 4.13.1.2):

8x full load current rating of motor

Overload protection is generally required for electric motors where the motor rating exceeds:

370W

A Star Delta-Starter requires how many wires connected to the motor?

6 wires

"Differential" thermal overload relays when used on electric motors provide:

Overload and phase failure protection

What is the maximum allowable resistance of an equipotential bonding conductor?

0.5 ohms

The maximum permitted resistance of the main earthing conductor in an installation is:

0.5 ohms

What is the mean tripping current of a Type C breaker?

7.5x

What is the mean tripping current of a Type D breaker?

12.5x

What is the mean tripping current of a Type B breaker?

4x

A reduced voltage motor starter is required for three-phase motors in a domestic installation where the starting current of the motor exceeds (SR: 1.17.2.4):

53A

How much voltage drop is allowed from the supply to a socket outlet?

5%

AS/NZS 3000 specifies various depths of laying for underground cabling. This depth of laying refers to the distance between the surface of the ground and (AS3000: 3.11.4.4):

The top of the cable/conduit.

What should the amp rating of a fuse be less than or equal to?

0.9xIz (Current carrying capacity)

What is the ambient temperature base used when determining the current carrying capacity of cables installed underground in Australia?

25 degrees celsius

What is the ambient temperature base used when determining the current carrying capacity of cables installed in air in Australia?

40 degrees celsius

The maximum disconnection time for protection against indirect contact for final subcircuits supplying 230V single-phase 10A socket-outlets is:

0.4 seconds

Who is covered by WHS Act when they enter a workplace?

All those that enter the site.

What does touch voltage mean?

Voltage between conductive parts when touched simultaneously

What does step voltage mean?

Voltage between 2 points, 1m apart on the earths surface

What is creepage distance?

Shortest distance along the surface of an insulating material between two conductors

What residual energy doesn't need to be discharged prior to work on electrical equipment?

A battery back-up supply