Electrical Engineering mock level 3 part 1

Describe how an electrician, working as a self-employed sole trader, can prove to potential customers a level of competence.

• By providing references from previous clients

• By showing a portfolio of completed projects

• By holding relevant certifications and qualifications

• By offering the lowest price for services

Calculate the approximate transformer ratio that would step down the maximum super grid voltage to 33 kV.

• 400:1

• 500:1

• 600:1

• 700:1

Determine, for the circuit shown below, the inductive reactance and impedance.

Calculate the phase current (IP) and phase voltage (VP) for the circuit shown below.

• I_P = V_P / √3 = 50 / √3 = 8.66 A

• V_P = V_L - √3 = 200 V

Answer explanation

To calculate phase current (IP), divide phase voltage (VP) by √3. IP = VP / √3 = 50 / √3 = 8.66 A. Therefore, the correct choice is I_P = V_P / √3 = 50 / √3 = 8.66 A.

List three component parts, within a d.c. compound motor, that involve a magnetic process.

• Armature, Field Coils, Commutator

• Brushes, Bearings, Shaft

• Rotor, Stator, Frame

• Capacitor, Resistor, Inductor

Answer explanation

The correct choice is Armature, Field Coils, Commutator as these components within a d.c. compound motor involve a magnetic process.

Calculate, for the luminaire shown below, the illuminance at point B.

• E = I / d^2 * cos(θ)

• d = √(side A^2 + side B^2)

• cos(θ) = side A / d

Answer explanation

The correct formula for illuminance at point B is E = I / d^2 * cos(θ), where I is the intensity, d is the distance, and θ is the angle of incidence.

State the maximum permitted disconnection times for each of the following circuits:

• A 230 V, 6 A, lighting circuit on a TN system.
• A 110 V, 16 A, socket-outlet on a construction site.
• A 400 V, 45 A, pump on a TT system.

Select the correct set of disconnection times:

• 1 second, 0.2 seconds, 5 seconds

• 0.4 seconds, 5 seconds, 1 second

• 5 seconds, 0.4 seconds, 1 second

• 0.4 seconds, 0.2 seconds, 5 seconds

Answer explanation

The correct set of disconnection times for the circuits are 0.4 seconds, 0.2 seconds, 5 seconds as per the regulations and safety standards.

A socket-outlet circuit in a public library is protected by a 32 A, RCBO to BS EN 61009. A) State the most suitable type to be used. B) Determine how quickly, in seconds, the RCBO would disconnect with a current of 100 A. C) State the component within the RCBO that would cause disconnection if a short circuit of 300 A occurred.

• Type B (C accepted with reason)

• Approx. 50 seconds (accept range of 30-80 if other type given in a) accept answer based on type)

• Magnetic trip

Answer explanation

The most suitable type for the RCBO is Type B. In case of a short circuit of 300 A, the magnetic trip component would cause disconnection.

A) Determine the maximum permissible rating for a lighting circuit containing B15 and B22 lamp-holders. B) Determine the current in the extra-low voltage section of a 12 V lighting circuit containing 3 x 50 W halogen lamps. C) Determine the most appropriate rating of BS 1362 fuse to be used in a fused connection unit supplying a 3 kW hand drier unit.

• 16 A

• 12.5 A

• 13 A (note BS 1362 fuse)

Answer explanation

The correct choice is 13 A (note BS 1362 fuse) as it is the most appropriate rating for the fused connection unit supplying a 3 kW hand drier unit.

An inspection is to be carried out to items within a distribution board during initial verification. Which of the following inspections would be undertaken?

• i) Sight: Checking for discoloration.

  ii) Touch: Feeling for excessive heat.

• i) Sight: Observing for correct labeling.

  ii) Touch: Testing for mechanical stability.

• i) Sight: Looking for signs of corrosion.

  ii) Touch: Checking for loose connections.

• i) Sight: Inspecting for proper installation.

  ii) Touch: Verifying texture of materials.

Answer explanation

The correct choice involves inspecting for signs of corrosion visually and checking for loose connections by touch, ensuring safety and proper functioning of the distribution board.