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Free Plumbing Practice Questions

10 free, exam-style NCCER Plumbing (Plumbing) practice questions with answers and explanations. No signup required. Work through them below, then take the full free Plumbing practice test to study every exam domain.

The Plumbing exam has 100 questions and runs 3 hours.

These 10 free Plumbing questions are organized by exam domain, so you can see how each part of the NCCER Plumbing blueprint is tested. Reveal the answer and explanation under each question.

Domain 1: Introduction to the Plumbing Profession 3% of exam

Question 1

Before a plumber enters a confined space such as a sewage wet well, what must be done FIRST?

  1. Test the atmosphere inside the space for hazards
  2. Put on an air-purifying full-face respirator first
  3. Station a trained attendant outside the entry point
  4. Open a second opening to create cross-ventilation
Show answer & explanation

Correct answer: A - Test the atmosphere inside the space for hazards

Question 2

A job specification calls for buried copper water service with the greatest wall thickness. Which type of copper tube should the plumber install?

  1. Type M
  2. Type DWV
  3. Type L
  4. Type K
Show answer & explanation

Correct answer: D - Type K

Question 3

A drawing dimension reads 5/8 inch, but the plumber's calculator works in decimals. What is 5/8 inch expressed as a decimal?

  1. 0.508 inch
  2. 0.580 inch
  3. 0.625 inch
  4. 0.875 inch
Show answer & explanation

Correct answer: C - 0.625 inch

Question 4

Which type of plumbing drawing shows a three-dimensional view of a piping system drawn along axes 30 degrees from horizontal?

  1. Isometric drawing
  2. Orthographic drawing
  3. Plan view drawing
  4. Schematic riser drawing
Show answer & explanation

Correct answer: A - Isometric drawing

Question 5

A homeowner reports a sewer-gas smell at a guest-bathroom floor drain that is almost never used. A trap's water seal is meant to block sewer gas from the room - so what has most likely happened here?

  1. The trap became partially clogged with solid debris
  2. The trap is undersized for the type of fixture served
  3. The trap's internal screen corroded and fell away
  4. The dry trap seal evaporated and no longer blocks gas
Show answer & explanation

Correct answer: D - The dry trap seal evaporated and no longer blocks gas

Question 6

When joining Schedule 40 PVC drainage pipe with solvent cement, what is the purpose of applying primer to the pipe and fitting before the cement?

  1. It softens the surfaces so the cement can fuse them
  2. It lubricates the joint so the fitting seats fully home
  3. It degreases the surface the way a wax cleaner would
  4. It speeds curing so the joint pressurizes much sooner
Show answer & explanation

Correct answer: A - It softens the surfaces so the cement can fuse them

Question 7

A plumber needs to tighten the supply nuts on a faucet located in the cramped space directly behind a bathroom sink. Which tool is designed for this task?

  1. Pipe wrench
  2. Basin wrench
  3. Strap wrench
  4. Spud wrench
Show answer & explanation

Correct answer: B - Basin wrench

Question 8

Two sections of hubless (no-hub) cast-iron soil pipe must be joined. Which component makes this connection?

  1. A poured lead-and-oakum joint packed in the hub
  2. A neoprene gasket in a stainless shielded clamp
  3. A solvent-welded socket-and-spigot connection
  4. A threaded coupling sealed with joint compound
Show answer & explanation

Correct answer: B - A neoprene gasket in a stainless shielded clamp

Question 9

On a lockout/tagout program, each worker applies their own lock and tag to an energy-isolating device. Why is the worker's OWN lock required, rather than one shared lock?

  1. So the crew's most senior member can clear all locks
  2. So locks can be color-coded by trade for inventory
  3. So only that worker can remove it while they work
  4. So the equipment can be restarted from a remote panel
Show answer & explanation

Correct answer: C - So only that worker can remove it while they work

Domain 2: Plumbing Safety 16% of exam

Question 10

Under the IPC, what is the minimum slope for a horizontal drainage pipe that is 2½ inches in diameter or smaller?

  1. 1/16 inch per foot
  2. 1/8 inch per foot
  3. 1/4 inch per foot
  4. 1/2 inch per foot
Show answer & explanation

Correct answer: C - 1/4 inch per foot

The rest of the Plumbing blueprint

The Plumbing exam also covers these domains. Drill them in the full free practice test:

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