012 Practice questions (C)

The top part of a distribution board must conform to?

• IP2X

• IPX2

• IP4X

• IP67

Answer explanation

The top part of a distribution board must conform to IP4X, which indicates protection against solid objects larger than 1mm. This ensures safety and compliance in electrical installations.

The correct formula for calculating earth fault loop impedance is?

• Zs=Ze-(R1+R2)

• Zs=Ze+(R1xR2)

• Zs=Ze+(R1+R2)

• Zs=Ze/(R1+R2)

Answer explanation

The correct formula for calculating earth fault loop impedance is Zs=Ze+(R1+R2). This accounts for the earth fault loop impedance (Zs) as the sum of the earth fault loop impedance (Ze) and the resistances (R1 and R2).

Which type of earthing system uses the armour/metallic sheath of the supply cable as the Earth?

• TT

• TN-C-S

• IT

• TN-S

Answer explanation

The TN-S earthing system uses the metallic sheath of the supply cable as the Earth. This provides a direct path for fault currents, enhancing safety and system reliability.

Which type of earthing system relies on the general mass of Earth as the Earth conductor?

• TT

• TN-C-S

• IT

• TN-S

Answer explanation

The TT earthing system uses the general mass of the Earth as the Earth conductor, providing a direct connection to the ground. This distinguishes it from other systems like TN-C-S, IT, and TN-S, which have different configurations.

Which type of earthing system uses a combined PEN conductor, external to the installation?

• TT

• TN-C-S

• IT

• TN-S

Answer explanation

The TN-C-S system uses a combined Protective Earth and Neutral (PEN) conductor, which is external to the installation. This distinguishes it from other systems like TT and IT, which do not utilize a combined PEN conductor.

An earth fault loop impedance test performed on a ring final circuit would record?

• the resistance of the protective conductor

• the resistance of the protective conductor and the line conductor

• the external loop impedance

• the resistance of the line conductor, protective conductor and external loop impedance

Answer explanation

An earth fault loop impedance test on a ring final circuit measures the total impedance, which includes the resistance of the line conductor, the protective conductor, and the external loop impedance.

A polarity test is conducted to verify that?

• every single pole device is connected to the line and neutral conductors

• the circuit protective conductors are correctly connected

• All conductors are terminated correctly, single pole devices terminated in the line only

• the resistance is high enough to operate the protective device within 0.4 seconds

Answer explanation

The polarity test ensures that all conductors are terminated correctly, confirming that single pole devices are connected to the line only, which is crucial for safe and proper circuit operation.

An RCD has an integral test button to check?

• the electrical function

• the mechanical function

• the disconnection time

• the RCD resistance

Answer explanation

The integral test button on an RCD is designed to check the mechanical function, ensuring that the device can trip and disconnect the circuit when necessary. It does not test electrical function, disconnection time, or resistance.

The easiest method of confirming polarity on a standard lighting circuit would be during?

• the earth electrode test

• the earth fault loop impedance test

• Continuity of cpc test method 1 (R1+R2)

• an insulation resistance test

Answer explanation

The Continuity of cpc test method 1 (R1+R2) allows for checking the polarity of the circuit by verifying the continuity of the conductors, making it the easiest method to confirm polarity in a standard lighting circuit.

A polarity test is performed on ES lampholders to?

• ensure the centre contact is not connected to the line conductor

• ensure the centre contact is connected to the line conductor

• ensure that there is no breakdown in insulation

• ensure that the cpc is continuous throughout the circuit

Answer explanation

A polarity test on ES lampholders ensures the centre contact is connected to the line conductor, which is crucial for safe operation and preventing electrical hazards.