NCCER Basic Electrical & Plumbing 3 — Questions and Answers
Question 1: A P-trap under a sink serves what primary function?
- Filtering debris from drain water
- Holding water to block sewer gases from entering the home (Correct answer)
- Increasing water pressure at the fixture
- Connecting supply and drain lines
Correct answer: Holding water to block sewer gases from entering the home
The P-trap holds a water seal that prevents toxic and odorous sewer gases from backing up into the living space through the drain.
Question 2: When replacing a standard light switch with a dimmer, what type of load must you verify the dimmer is rated for?
- Only the voltage rating matters
- The wattage and type of bulbs (LED, incandescent, CFL) (Correct answer)
- The amperage of the circuit breaker only
- The distance to the electrical panel
Correct answer: The wattage and type of bulbs (LED, incandescent, CFL)
Dimmers must be matched to the bulb type and total wattage; LED dimmers differ from incandescent dimmers, and mismatches cause flickering or fixture damage.
Question 3: What is the purpose of a pressure-relief valve (PRV) on a water heater?
- To adjust the water temperature setting
- To drain the tank for maintenance
- To release pressure if tank pressure or temperature exceeds safe limits (Correct answer)
- To filter sediment from the water supply
Correct answer: To release pressure if tank pressure or temperature exceeds safe limits
The T&P (temperature and pressure) relief valve is a safety device that opens automatically to prevent catastrophic tank rupture if pressure or temperature becomes dangerously high.
Question 4: In a 240V dryer circuit, what two conductors carry current to the appliance (excluding ground)?
- Two neutral wires
- One hot and one neutral wire
- Two hot wires (legs) at opposite phases (Correct answer)
- Two ground wires
Correct answer: Two hot wires (legs) at opposite phases
A 240V circuit uses two hot legs from opposite phases of the electrical panel, each carrying 120V, to deliver 240V to the appliance.
Question 5: What material is most commonly used for residential supply water pipes in new construction today?
- Cast iron
- Lead
- PEX (cross-linked polyethylene) (Correct answer)
- Galvanized steel
Correct answer: PEX (cross-linked polyethylene)
PEX tubing is the dominant material in modern residential plumbing due to its flexibility, freeze resistance, ease of installation, and durability.
Question 6: When testing a circuit with a non-contact voltage tester, the tester beeps near a wire but the breaker is OFF. What should you do?
- Proceed since the breaker is off
- Check if multiple circuits share the same breaker or if back-feed exists (Correct answer)
- Assume the tester is broken
- Cut the wire immediately
Correct answer: Check if multiple circuits share the same breaker or if back-feed exists
Voltage presence with the breaker off indicates either back-feed from another circuit, a shared neutral, or a miswired panel, all of which are hazardous.
Question 7: What does 'sweating a copper pipe' refer to in plumbing?
- Condensation forming on cold pipes
- Soldering copper pipe joints using heat and solder (Correct answer)
- Pressure-testing the pipe for leaks
- Insulating pipes to prevent heat loss
Correct answer: Soldering copper pipe joints using heat and solder
Sweating copper pipe means using a torch to heat the joint and wicking solder into the gap by capillary action to create a watertight connection.
NCCER Basic Electrical & Plumbing 3
A P-trap under a sink serves what primary function?