Journeyman Electrician’s Exam Journeyman Electrician's Overcurrent Protection 4

Question 1

A dual-element time-delay fuse is particularly useful for protecting circuits with:

Accepted Answer

Motor loads with high inrush currents

Answer

Dual-element time-delay fuses tolerate the high inrush current of motor starting while still protecting against sustained overloads.

Question 2

Under NEC 230.91, where must the service overcurrent protective device be installed?

Accepted Answer

At the first accessible point after the service entrance conductors enter the building

Answer

NEC 230.91 requires the service OCPD to be an integral part of the service disconnecting means located at the first accessible point of entry.

Question 3

What maximum number of overcurrent devices may serve as the service disconnecting means for a single building under NEC 230.71?

Accepted Answer

Six

Answer

NEC 230.71(A) limits the service disconnecting means to a maximum of six switches or circuit breakers for a single service.

Question 4

A 40-ampere, 240-volt branch circuit feeds an electric range. The range's nameplate rating is 8.75 kW. Is this circuit properly protected?

Accepted Answer

Yes, 40 amperes satisfies the demand calculation

Answer

NEC 220.55 and Table 220.55 allow demand factors; a 40A circuit is the minimum required for an 8.75 kW range and is acceptable.

Question 5

Current-limiting fuses reduce the let-through energy during a fault primarily by:

Accepted Answer

Clearing the fault in less than one-half cycle

Answer

Current-limiting fuses clear high-magnitude faults in less than a half cycle (0.00833 s), drastically reducing let-through I²t energy.

Journeyman Electrician’s Exam Practice Test