Electrical design L3 B

Co-ordination of fuses during fault or overload conditions is known as:

• diversity

• diverging

• discrimination

• deviation.

A circuit-breaker has two modes of operation:

• overload due to thermal effect or short circuit due to a magnetic trip

• overload due to a magnetic trip or short circuit due to thermal effect

• overload due to a chemical reaction or short circuit due to a magnetic trip

• overload due to a thermal trip or chemical reaction due to a magnetic trip.

An MCB rated at 40 A will trip:

• only when a short circuit occurs

• only when an overload occurs

• when an overload, short circuit or earth fault occurs

• when 41 A flows through it.

An RCD rated at 30 mA will trip:

• when enough current flows to earth

• through an earth fault or an overload

• through an overload, short circuit or earth fault

• when 30 mA flows.

What type of MCB is associated with commercial applications especially fluorescent lighting?

• Type 3

• Type B

• Type C

• Type D

Which device will detect an imbalance between line and neutral, overloads and all types of overcurrent faults?

• RCD

• RCBO

• MCB

• SPD

An RCD protects:

• the person

• the switch

• the cable

• the load.

A value that ensures that a circuit-breaker can withstand a fault current is known as:

• breaking capacity

• rating

• thermal constraint

• shock protection

Which earthing system is not recommended for petrol stations, caravans and marina pontoons?

• TNS

• TT

• TNC

• PME

What is the maximum tabulated value of Ze for a TN-C-S system?

• 0.8 Ω

• 0.35 Ω

• 20 Ω

• 1.75 Ω