Earthing and Bonding Quiz

Which Earthing system has an Earth Electrode at the substation transformer and at the consumers premises, and uses the 'general mass of earth' as the main earthing conductor between the two?

• TN-S system

• TN-C-S system

• TT system

• TN-C system

Answer explanation

The TT system features an Earth Electrode at both the substation transformer and the consumer's premises, utilizing the 'general mass of earth' as the main earthing conductor, distinguishing it from other systems.

Which Earthing system has an Earth Electrode at the supply transformer and uses the 'metallic sheathing of a supply cable' as the main earthing conductor between the supply transformer and the consumers premises?

• TT system

• TN-C system

• TN-S system

• TN-C-S system

Answer explanation

The TN-S system features an Earth Electrode at the supply transformer and utilizes the metallic sheathing of the supply cable as the main earthing conductor, ensuring effective earthing between the transformer and consumer premises.

What name is given to the 'combined' Earth and Neutral conductor in a TN-C-S Earthing system?

• SEN

• PEN

• TEN

• LEN

Answer explanation

In a TN-C-S earthing system, the combined Earth and Neutral conductor is referred to as PEN (Protective Earth and Neutral). This term is essential for understanding the system's grounding and safety features.

Which Earthing system has an Earth Electrode at the supply transformer and uses a 'combined Neutral and Earth conductor' as the main earthing conductor between the supply transformer and the consumers premises?

• TN-S system

• TN-C system

• TT system

• TN-C-S system

Answer explanation

The TN-C-S system features an Earth Electrode at the supply transformer and utilizes a combined Neutral and Earth conductor for the main earthing connection to the consumer's premises, distinguishing it from other systems.

What is the 'average' assumed impedance of a 'TT' system?

• 0.8 ohms

• 0.35 ohms

• 21 ohms

• 10 ohms

Answer explanation

The average assumed impedance of a 'TT' system is typically around 21 ohms. This value is used for calculations related to grounding and electrical safety in such systems.

What is the 'average' assumed impedance of a 'TN-S' system?

• 10 ohms

• 0.8 ohms

• 0.35 ohms

• 21 ohms

Answer explanation

The average assumed impedance of a TN-S system is typically around 0.35 ohms. This low impedance helps ensure effective fault current paths and enhances safety in electrical installations.

What is the 'average' impedance of a 'TN-C-S' system?

• 21 ohms

• 0.8 ohms

• 10 ohms

• 0.35 ohms

Answer explanation

The average impedance of a TN-C-S system is typically around 0.35 ohms, which is crucial for ensuring effective fault protection and minimizing voltage drop in electrical installations.

Which Earthing System MUST have a (main) R.C.D as additional protection?

• TN-C

• TN-C-S

• TN-S

• TT

Answer explanation

The TT earthing system requires a main R.C.D for additional protection due to its reliance on a separate earth electrode, which can lead to higher touch voltages. This enhances safety against electric shock.

What is the operating principle of a Residual Current Device (RCD)?

• thermal overload

• current balance

• voltage balance

• magnetic overload

Answer explanation

The operating principle of a Residual Current Device (RCD) is based on current balance. It detects imbalances between the live and neutral currents, indicating a leakage current, and disconnects the circuit to prevent electric shock.

When calculating 'fault current', which 'ohms law' formula would be used?

• I = V + R

• I = R x V

• I = V/R

• I = R/V

Answer explanation

The correct formula for calculating fault current is I = V/R, where I is current, V is voltage, and R is resistance. This formula derives from Ohm's Law, which states that current is equal to voltage divided by resistance.