Free TN-LLE Fault Current & OCPD Ratings Questions and Answers

Question 1

The marking 'AIC' on a circuit breaker or fuse stands for:

Accepted Answer

Ampere Interrupting Capacity

Answer

Amperes in Continuous-duty

Answer

Alternating Inductive Current

Answer

Available Instantaneous Current

Question 2

According to NEC 110.9, an overcurrent protective device's interrupting rating must be:

Accepted Answer

Equal to or greater than the available fault current.

Answer

Less than the available fault current.

Answer

Equal to the circuit's continuous load.

Answer

Exactly 125% of the conductor ampacity.

Question 3

Which of the following actions would most likely INCREASE the available fault current at a panelboard?

Accepted Answer

Replacing the upstream transformer with a larger kVA unit

Answer

Increasing the length of the feeder conductors

Answer

Using smaller gauge feeder conductors

Answer

Adding more non-continuous loads to the panel

Question 4

A panelboard is marked "Suitable for use as service equipment only when not more than six main circuit breakers are installed." This is an example of what NEC rule?

Accepted Answer

The Six Disconnect Rule (230.71)

Answer

The Tap Rule (240.21)

Answer

The Series Rating Rule (240.86)

Answer

The Interrupting Rating Rule (110.9)

Question 5

What is required for a 'series rated' overcurrent protection system to be compliant with the NEC?

Accepted Answer

The combination must be specifically tested and listed for series use.

Answer

Both devices must be from the same voltage class.

Answer

The load-side breaker must have at least half the AIC of the line-side breaker.

Answer

The system must be designed by a licensed professional engineer.

Question 6

The general rule in NEC 240.21 requires that overcurrent protection for a conductor be located:

Accepted Answer

At the point where the conductor receives its supply.

Answer

At the midpoint of the circuit run.

Answer

At the load end, nearest the equipment.

Answer

Within a readily accessible junction box.