General Contractor License Mechanical, Electrical, and Plumbing Systems

Question 1

Under the National Electrical Code (NEC), what is the minimum burial depth for a residential underground feeder (UF) cable installed without conduit?

Accepted Answer

18 inches

Answer

NEC requires UF cable to be buried at least 24 inches deep in most residential applications, but 18 inches when the circuit is GFCI-protected and limited to 120V/20A.

Question 2

Which type of pipe is most commonly required by code for natural gas supply lines inside a residential structure?

Accepted Answer

Black steel pipe

Answer

Black steel pipe is the standard code-approved material for interior natural gas supply lines because it is durable and does not corrode from gas contact.

Question 3

According to the IRC, what is the required minimum headroom clearance for a residential stairway?

Accepted Answer

6 feet 8 inches

Answer

The IRC requires a minimum headroom clearance of 6 feet 8 inches measured vertically from the stair nosing to any overhead obstruction.

Question 4

When sizing a residential water heater, which factor is the MOST important determinant of required capacity?

Accepted Answer

First Hour Rating (FHR)

Answer

The First Hour Rating (FHR) indicates how many gallons a water heater can supply in the first hour of use, making it the primary sizing factor for residential demand.

Question 5

In a residential electrical panel, a double-pole 240V breaker that trips on only one leg is an indication of what condition?

Accepted Answer

A failed breaker requiring replacement

Answer

A double-pole breaker that trips on only one side indicates the breaker mechanism has failed internally and the entire breaker must be replaced.

General Contractor License Practice Test

General Contractor License Practice Test

General Contractor License Mechanical, Electrical, and Plumbing Systems