2. Inspection and Testing EAL

OSG gives the maximum stable value of Ze for a TT installation as:

• 1660 ohms

• 600 ohms

• 200 ohms

• 100 ohms

Answer explanation

The maximum stable value of Ze for a TT installation is specified as 200 ohms. This value is critical for ensuring safety and compliance with electrical standards, making 200 ohms the correct choice.

Which type of earthing system relies on a separately supplied earth, usually the sheathing on the cable:

• TT

• TN-C-S

• IT

• TN-S

Answer explanation

The TN-S earthing system uses a separate earth conductor, typically the sheathing of the cable, ensuring safety and reliability. This distinguishes it from other systems like TT and IT, which have different earthing configurations.

Which of the following would not be one of the human senses to use during the initial verification of an addition to a lighting circuit:

• Sight

• Hearing

• Taste

• Touch

Answer explanation

Taste is not a human sense used for verifying electrical circuits. The other senses—sight, hearing, and touch—are essential for assessing the safety and functionality of a lighting circuit.

On a standard TT installation, the result of the resistance of the earth electrode and the rated RCD residual operating current should not exceed:

• 25V

• 50V

• 110V

• 400V

Answer explanation

The maximum allowable voltage for a TT system, considering the resistance of the earth electrode and the rated RCD residual operating current, is 50V. This ensures safety by limiting touch voltage in case of a fault.

Which of the following protection devices is unlikely to be suited for short circuit currents in the region of 6kA:

• BS 3036 semi-enclosed fuse

• BS 88-3 cartridge fuse

• BS 88-2 general purpose fuse

• BS EN 60898 circuit breaker

Answer explanation

The BS 3036 semi-enclosed fuse is not designed to handle high short circuit currents like 6kA, making it unsuitable compared to the other options, which are better equipped for such conditions.

The term given to the person responsible for an electrical system is the:

• Competent person

• Electrician

• Duty holder

• Company manager

Answer explanation

The term 'Duty holder' refers to the individual responsible for ensuring the safety and compliance of an electrical system, making it the correct choice over 'Competent person', 'Electrician', or 'Company manager'.

Regional electricity companies quote a maximum likely value of external loop impedance (outside the consumer's installation) for a TN-S system as:

• 0.35 ohm

• 0.8 ohm

• 21 ohm

• 200 ohm

Answer explanation

In a TN-S system, the maximum external loop impedance is specified to ensure safety and proper operation. The correct value is 0.8 ohm, which is the standard limit set by regional electricity companies for such systems.

EAW Regulations state that working live is acceptable unless:

• Suitable tools are used

• Suitable PPE is worn

• It is reasonable in all circumstances for it to be dead

• An engineer gives you permission

Answer explanation

EAW Regulations allow live working unless it is reasonable in all circumstances for it to be dead. This ensures safety and compliance, making the correct choice essential.

Overloaded windings on a 3 phase motor may be identified in the first instance by using which sense:

• Sight

• Smell

• Touch

• Taste

Answer explanation

Overloaded windings in a 3 phase motor can produce a burning smell due to insulation breakdown. Therefore, the sense of smell is the first indicator to identify such issues, making it the correct choice.

Which of the following earthing systems has the path for earth leakage currents via the earth itself:

• TN-S

• TNC-S

• TN-C

• TT

Answer explanation

The TT earthing system allows earth leakage currents to flow directly into the ground, providing a path for fault currents via the earth itself, unlike TN systems which use neutral conductors.