IEC Overcurrent Protection 3

Question 1

An inverse-time circuit breaker trips faster when the overcurrent is:

Accepted Answer

Much larger than its rated amperage

Answer

Inverse-time breakers have a trip time that decreases as the magnitude of overcurrent increases.

Question 2

Per NEC 240.85, a circuit breaker marked '120/240V, 2-pole' may be used on which system?

Accepted Answer

120/240V single-phase systems

Answer

A breaker must be rated for the voltage of the system it protects; a 120/240V 2-pole breaker is rated for 120/240V single-phase systems.

Question 3

Which NEC section covers the location requirements for overcurrent devices in dwelling units?

Accepted Answer

NEC 240.24

Answer

NEC 240.24 specifies where overcurrent devices shall and shall not be located, including dwelling unit requirements.

Question 4

A 20A, 120V branch circuit supplies a single receptacle. The cord-and-plug-connected load must not exceed what amperage for continuous operation?

Accepted Answer

16A

Answer

Continuous loads on a branch circuit must not exceed 80% of the circuit rating (20A × 80% = 16A).

Question 5

What is the primary difference between a Type T and a Type W Class K fuse?

Accepted Answer

Interrupting rating and let-through current

Answer

Class K fuses are subdivided by let-through current and interrupting ratings; Type W has higher let-through than Type T.

IEC - Independent Electrical Contractors Practice Test