Earthing and Bonding-OSG

Which 1 of the following is an example of an extraneous-conductive part?

• Metallic water installation pipes

• Steel conduit

• Metallic socket

• Steel trunking

Answer explanation

The other three are examples of EXPOSED-conductive parts. Conductive parts of equipment/installation that are NOT normally but can be if basic insulation fails.

What size earthing conductor would a 25mm mains distribution cable require for a TN-S supply?

• 6mm

• 10mm

• 25mm

• 16mm

Answer explanation

Section 4.4 Earthing conductor and main protective bonding conductor CSA-Table 4.4 (i)

Which of the following are types of earth electrode?

• Earth rods or pipes

• Earth tapes

• Steel pipes

• Aluminium rods

Answer explanation

Section 4.10- List of earth electrodes. These are used for installations that require a TT earthing arrangement. The common type is the earth rod shown in the image.

What is the recommended maximum earth fault loop impedance for a TT earthing arrangement?

• 100 Ohms

• 150 Ohms

• 200 Ohms

• 30 Ohms

Answer explanation

Although it is recommended that a TT earthing arrangement does not exceed 200 ohms the value of 21 Ohms is the usual stated reading. Anything over 200 Ohms can become unstable due to environmental changes such as summer and winter.

There is a yellow plastic incoming gas pipe in a domestic property. Is main protective bonding a requirement or a recommendation?

• Recommendation

• Requirement

Answer explanation

Main protective bonding is NOT REQUIRED on plastic incoming services but IS RECOMMENDED. Section 4.5, page 57.