The miniature circuit breaker (MCB) with ____ trip characteristics trips instantaneously when the current flowing through it reaches between 10 to 20 times the rated current.

• A. Class C
• B. Class B
• C. Class Z
• D. Class D

Answer: (D)

Type B MCB:
Type B devices are generally suitable for domestic applications.
They are designed to trip at fault currents of 3 - 5 times rated current.

Type C MCB:
Type C devices are the normal choice for commercial and industrial applications
These devices are designed to trip at 5 - 10 times rated current

Type D MCB:
The Type D devices have more limited applications, normally in industrial use where high inrush currents may be expected.
Type D devices are designed to trip at 10 - 20 times.