How many questions is the Plumber (306A) Red Seal exam?

125 multiple-choice questions across 7 Major Work Activities, with a 4-hour time limit and a 70% pass mark, set by the Red Seal Occupational Standard and identical in every province.

Which authority administers the Plumber (306A) Red Seal exam in Ontario?

In Ontario, exam application, trade qualifier assessment, and exam sitting scheduling are administered by Skilled Trades Ontario (STO).

Red Seal Pass › Plumber (306A) › Ontario

Plumber (306A) Red Seal Exam in Ontario

Q: Do I need a Red Seal certificate to work as a Plumber (306A) in Ontario?

Yes. Ontario lists this trade as compulsory (Plumber (306A)), so workers must hold a valid Certificate of Qualification, a Provisional Certificate of Qualification, or a Registered Training Agreement; journeypersons must renew their C of Q each year.

Certifying authority: Skilled Trades Ontario (STO). Last checked 2026-09-10.

Certification is required in Ontario

This trade is on Ontario’s compulsory list as Plumber (306A). Under Skilled Trades Ontario, workers must hold a valid Certificate of Qualification, a Provisional Certificate of Qualification, or a Registered Training Agreement; journeypersons must renew their C of Q each year. Official list PDF is dated Feb 2022; the count of 23 still matches the current STO page.

Source: Skilled Trades Ontario — Compulsory Trades (23 trades)

Preparing for the Plumber (306A) exam in Ontario?

Start with 10 free interactive Plumber (306A) questions with worked explanations, or take a full 125-question timed mock exam weighted to the official RSOS breakdown.

Try the 10-Question Interactive Plumber (306A) Quiz & Free PDF → Take Full 125-Question Timed Mock Exam ($14.99 CAD) →

Or unlock all Plumber (306A) questions with the 7-Day Pass ($9.99) or 3-Month Pass ($69.99, Free-Until-You-Pass Guarantee).

Whether it is required or not, the exam itself is the same paper everywhere in Canada. What your province decides is whether you must hold the certificate, how you apply, and where you sit it.

The exam: 125 questions, 7 Major Work Activities

The Red Seal Occupational Standard sets the split below. It does not change by province.

Major Work Activity	Weighting	Questions
MWA A: Performs common occupational skills	11%	14 Qs
MWA B: Prepares and assembles tube, tubing and pipe	10%	13 Qs
MWA C: Installs, tests and services sewers, sewage treatment systems and drainage, waste and vent (DWV) systems	26%	32 Qs
MWA D: Installs, tests and services water service and distribution	19%	24 Qs
MWA E: Installs, tests and services fixtures, appliances and water treatment systems	14%	17 Qs
MWA F: Installs, tests and services low-pressure steam and hydronic systems	13%	16 Qs
MWA G: Installs, tests and services specialized systems	7%	9 Qs

Source: Red Seal Exam Breakdown — Plumber (306A), red-seal.ca

Time allowed and pass mark

4 hours, and a 70% pass mark (88/125). These are set provincially rather than by the Red Seal standard, and the four hours is the same whether your paper is 100 or 150 questions.

Confirmed against Skilled Trades Ontario’s Exam Preparation Guide and SkilledTradesBC. Check your own authority before exam day.

Quick 3-Question Plumber (306A) Readiness Check

Click any option (A–D) below to grade yourself immediately and view the worked explanation:

Sample Question 1 of 3

While solvent-welding Schedule 40 PVC drainage fittings in a commercial mechanical room in Laval, a plumber splashes PVC cement onto the bare forearm. The skin starts to sting and the apprentice runs to the binder of WHMIS 2015 Safety Data Sheets kept by the door. Which section of the SDS gives the immediate first-aid steps for this exposure?

A) Section 7, Handling and Storage, with the safe-use rules for the cement

B) Section 11, Toxicological Information, with the health effects of each route

C) Section 4, First-Aid Measures, with the immediate treatment for skin contact

D) Section 2, Hazard Identification, with the pictograms and hazard warnings

Correct answer: C

WHMIS 2015 SDSs have 16 sections in a fixed order. Section 4, First-Aid Measures, gives the symptoms and the immediate treatment for each route of exposure. Section 7 covers handling and storage, Section 11 the health effects in detail, and Section 2 the hazard warnings and pictograms.

Sample Question 2 of 3

A new office building in downtown Ottawa is going up where the city storm sewers are near capacity, and the city limits how fast the site may release storm water. The structural engineer has designed the flat roof to carry the weight of water held on it during a storm, and the drawings show no storage tank on the site. Which roof drains will the engineer specify for this roof?

A) Siphonic roof drains, which empty the roof faster than gravity drains of the same size

B) Controlled-flow roof drains, whose weirs hold water on the roof and release it slowly

C) Sump-type roof drains, whose deep receivers drain the roof before ponding can begin

D) Overflow roof drains with raised dams, which take water only when ponding is deep

Correct answer: B

Controlled-flow roof drains have weirs that limit the flow, so the roof itself stores the storm water and releases it slowly to the city sewer, which is why the roof is designed for the weight. Siphonic and sump-type drains empty the roof faster, the opposite of what the city wants, and overflow drains are an emergency backup, not the primary control.

Sample Question 3 of 3

You must drill twelve 16 mm holes, each 100 mm deep, into the cured concrete floor slab of a school washroom to take the wedge anchors for four water closet carriers. The anchor maker's sheet calls for holes drilled with a carbide-tipped bit to the anchor's diameter, and does not allow diamond-cored holes. Which tool should you use to drill the anchor holes?

A) A rotary hammer with a carbide-tipped bit the same diameter as the anchors

B) A cordless impact driver with a carbide-tipped masonry bit of the same size

C) A wet diamond core drill with a 16 mm core bit, which leaves a clean hole

D) A drill driver in plain drill mode with a 16 mm high-speed steel twist bit

Correct answer: A

A rotary hammer drives a carbide-tipped bit into concrete with a hammering action and cuts the rough-walled hole a wedge anchor grips. An impact driver hammers around its axis, not along it, and does not drill concrete well; a diamond core is ruled out by the anchor maker; a high-speed steel twist bit with no hammer action dulls at once in concrete.

Where you write it in Ontario

Humber College Centre for Trades & Technology — Toronto / Etobicoke, ON
GTA central examination center
George Brown College (Casa Loma Campus) — Toronto, ON
Downtown Toronto trades testing center
Mohawk College (Stoney Creek Campus) — Hamilton, ON
Golden Horseshoe regional testing center
Conestoga College (Cambridge Campus) — Kitchener-Waterloo, ON
Southwestern Ontario testing hub
Algonquin College — Ottawa, ON
Eastern Ontario capital region testing facility

Booking is handled by Skilled Trades Ontario (STO); confirm current locations and dates with them.

Preparing for the Plumber (306A) exam

Our Plumber (306A) question bank is built to the official RSOS weighting above, with a worked explanation and code citation on every question.

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