Free TN-LLE Fault Current & OCPD Ratings Questions and Answers 1

Question 1

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

Accepted Answer

Ampere Interrupting Capacity

Answer

AIC stands for Ampere Interrupting Capacity, also known as the Interrupting Rating (IR). This rating indicates the maximum amount of fault current that the overcurrent protective device (OCPD) can safely interrupt without failing or causing a hazard.

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

NEC 110.9 is a fundamental safety rule stating that equipment intended to interrupt current at fault levels must have an interrupting rating sufficient for the current that is available at the line terminals of the equipment. This means the device's rating must be equal to or greater than the available fault current.

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

The size of the upstream transformer is a primary factor in determining available fault current; a larger kVA transformer has a lower internal impedance and can deliver more current during a fault. Longer or smaller conductors would add impedance and decrease fault current.

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

This marking relates directly to NEC 230.71, which permits up to six switches or circuit breakers to serve as the service disconnecting means. The panelboard's listing and marking ensure it is used in compliance with this 'six-handle rule' for service equipment.

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

NEC 240.86 allows for series ratings where a line-side device (like a main breaker) with a high AIC rating can protect a load-side device (like a branch breaker) with a lower AIC rating. For this to be compliant, the combination of devices must be specifically tested and listed by the manufacturer for that purpose.

TN LLE - Tennessee Limited Licensed Electrician Practice Test

TN LLE - Tennessee Limited Licensed Electrician Practice Test

Free TN-LLE Fault Current & OCPD Ratings Questions and Answers 1