Five free practice questions on manuals, drawings and diagrams: module 6 of the nine modules of Ontario's Gas Technician 3 (G3) certificate exam, which TSSA runs. The exam is all multiple choice; these have four options and one correct answer, as every question in our bank does. Answer each one before opening the explanation. No account, no email.
01The questions
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A manual valve is wanted on a section of house piping that operates at 2 psig (13.8 kPa). The valve's specification sheet gives its maximum operating pressure as 0.5 psig (13.8 in. w.c.; 3.45 kPa). May it be used there?
- Not there; its rating is below that piping's pressure.
- Yes; both figures come to 13.8, so the rating is met.
- Yes; a pressure rating applies only during a pressure test.
- Not without first passing a leak test at 2 psig (13.8 kPa).
Show the answer
A. Correct. Product literature sets the conditions a component is rated for; 2 psig (13.8 kPa) is four times the valve's 0.5 psig (3.45 kPa) maximum, so it cannot go on that section. Choose a valve whose specification covers at least 2 psig, or use this one only where the pressure is within its rating.
Why not the others
B. The two 13.8 figures are in different units: the piping's 2 psig is 13.8 kPa, while the valve's 0.5 psig is 13.8 in. w.c. Converted alike, 2 psig is 55.4 in. w.c., four times the valve's limit.
C. A maximum operating pressure is the most the valve may see in service, not a test-only figure. 2 psig is four times the 0.5 psig rating, so this valve does not suit that section.
D. A leak test shows tightness on the day; it does not raise a component's rated pressure. The valve is rated for 0.5 psig and the piping runs at 2 psig, so it cannot be used there.
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A G.3 has measured an existing gas run on site at 16 ft (4.88 m) and wants to check it against the basement plan, which is drawn at 3/8 in. = 1 ft 0 in. (1:32). How long should that run scale on the print?
- 4 in. (102 mm)
- 6 in. (152 mm)
- 8 in. (203 mm)
- 12 in. (305 mm)
Show the answer
B. Correct. Each foot on site is 3/8 in. on the print, so 16 × 0.375 = 6 in.; in metric, 4 877 mm ÷ 32 = 152 mm. If the print scales to something else, the drawing or the site measurement needs a second look before work goes on from it.
Why not the others
A. 4 in. is what 16 ft scales at 1/4 in. = 1 ft (16 × 0.25), not the plan's scale. At 3/8 in. per foot: 16 × 0.375 = 6 in. (152 mm).
C. 8 in. is what 16 ft scales at 1/2 in. = 1 ft (16 × 0.5), a different scale from the title block's. At 3/8 in. per foot the run scales 6 in. (152 mm).
D. 12 in. is what 16 ft scales at 3/4 in. = 1 ft (16 × 0.75), reading the wrong scale on the rule. At 3/8 in. per foot the run scales 6 in. (152 mm).
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On a furnace schematic the high-limit switch is drawn closed and marked normally closed, opening at 88 °C (190 °F). On an overheated furnace a meter shows that switch open. What does this say about the drawing?
- it is correct; schematics show switches as they are after a fault
- it is wrong; it should show the switch as it is found in service
- it is wrong; a normally closed switch should never be found open
- it is correct; switches are drawn at rest, not as they are now
Show the answer
D. Correct. Schematics show every switch and contact in its de-energized, at-rest state. A normally closed limit is drawn closed and opens when it reaches its setting, so finding it open on an overheated furnace agrees with the drawing; the cause of the overheating is what needs finding.
Why not the others
A. Schematics show the at-rest state, not a fault state. The limit is drawn closed because that is its normal state; it opened because the furnace overheated.
B. A schematic cannot show switches as found, because their state changes with operation; the convention is the at-rest state. The drawing is right, and the open limit is responding to the high temperature.
C. Normally closed describes the at-rest state; a limit is meant to open when its temperature setting is reached. Finding it open on an overheated furnace is the limit doing its job.
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A pie chart of a house's yearly gas use shows furnace 62 %, water heater 24 %, dryer 8 % and range 6 %. Total use was 2 400 m³ (84 800 ft³). How much gas did the water heater use?
- 57.6 m³ (2 030 ft³)
- 192 m³ (6 780 ft³)
- 576 m³ (20 300 ft³)
- 1 488 m³ (52 500 ft³)
Show the answer
C. Correct. Each slice is that share of the whole: 0.24 × 2 400 = 576 m³; 576 ÷ 0.028 317 = 20 300 ft³. The slices add to 100 %, a quick check that the chart has been read right.
Why not the others
A. This reads 24 % as 2.4 % (0.024 × 2 400 = 57.6). A percentage is per hundred: 0.24 × 2 400 = 576 m³ (20 300 ft³).
B. 192 m³ is the dryer's 8 % slice (0.08 × 2 400), not the water heater's. The water heater's 24 %: 0.24 × 2 400 = 576 m³ (20 300 ft³).
D. 1 488 m³ is the furnace's 62 % slice (0.62 × 2 400). The water heater's 24 % is 0.24 × 2 400 = 576 m³ (20 300 ft³).
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A propane water heater's rating plate gives a minimum inlet pressure of 11.0 in. w.c., and the digital manometer is set to read in kPa. Taking 1 in. w.c. = 0.2491 kPa, what reading matches the plate minimum?
- 0.40 kPa
- 2.74 kPa
- 44.2 kPa
- 2 740 kPa
Show the answer
B. Correct. 11.0 × 0.2491 = 2.74 kPa, which a manometer set to pascals shows as 2 740 Pa. Setting the instrument's unit before reading avoids comparing figures in two different units.
Why not the others
A. 0.40 is the pressure in psi (11.0 ÷ 27.68), labelled as kPa. In kPa: 11.0 × 0.2491 = 2.74 kPa.
C. This divides by the factor instead of multiplying (11.0 ÷ 0.2491 = 44.2). Each inch of water column is 0.2491 kPa: 11.0 × 0.2491 = 2.74 kPa.
D. 2 740 is the reading in pascals; 2 740 Pa is 2.74 kPa. Labelling pascals as kilopascals overstates the pressure a thousandfold.
02Answer key
| Question | Answer | Learning outcome |
|---|---|---|
| Q1 | A | Using specifications and product literature to select or check equipment |
| Q2 | B | Detail and assembly drawings, symbols and scale |
| Q3 | D | Schematic (ladder) diagrams and pictorial wiring diagrams |
| Q4 | C | Line graphs, bar and pie charts and when each is used |
| Q5 | B | Imperial and SI units in gas work: in. w.c., psig, kPa, Btuh, kW, ft3/h, m3/h |
03What module 6 covers
Reading the documents a gas technician works from: certified installation and operating instructions, rating plates and labels, specifications and product literature, orthographic, isometric, detail and assembly drawings with their symbols and scale, schematic and wiring diagrams, graphs, charts and tables, and the imperial and SI units of gas work and how to convert between them.
TSSA names module 6 “Technical Manuals, Specifications, Schematics, Drawings and Graphs”. It gives its G3 curriculum only to accredited training providers, so the five objectives below are TicketPrep's own, built from public sources such as college course outlines and Ontario's regulations, not TSSA's. TSSA does not publish the G3 question count or how many exam questions come from each module: its prep guide gives no G3 count and no per-module count, and candidates who fail get a mastery report broken down by module. The right-hand column is how many questions our bank holds on each objective, Standard and Advanced together, not a count from the exam.
| Our objective | In our bank |
|---|---|
| Objective 6.1 Use manufacturers' manuals, specifications and reference materials | 8 |
| Objective 6.2 Read mechanical drawings | 7 |
| Objective 6.3 Read schematics and wiring diagrams | 5 |
| Objective 6.4 Read graphs, charts and tables | 5 |
| Objective 6.5 Use units of measurement and conversion factors | 5 |
04What the questions turn on
The rating plate sets the limits
Supply pressure read at the inlet tap is checked against the plate's minimum and maximum inlet figures; the manifold pressure is a separate figure, set by the gas control's regulator. A plate in SI units is read the same way once the reading is converted. The plate also names the gas the appliance is certified for: a heater marked for natural gas only, with no conversion listed, stays off a propane supply.
Product literature decides what goes on the job
Product literature states what a sealant is made for, and propane can attack a compound not formulated for it, so propane piping gets a sealant listed for propane. Certified instructions can set conditions on other work too: a water heater whose instructions say to disconnect it for any piping test above 1/2 psi comes off the line, with the end capped, for a 5 psig test.
An isometric shows the route; the dimensions give the length
On a piping isometric a vertical line is a riser or a drop, and the two horizontal directions are drawn at 30° either side of horizontal. Isometrics are not drawn to scale, so pipe is cut to the written dimensions. The total length for the test tag is the sum of every leg, horizontal and vertical.
Read a schematic rung by rung
A schematic lays a circuit out by function, so the switches ahead of the gas valve read straight across a rung. Every switch in a series string must close before the control gets power: with the pressure switch open, neither the igniter nor the gas valve is powered, though the inducer keeps running. Energizing a relay coil changes every contact that carries its label.
05The other modules
The G3 exam covers nine modules, 1 to 9. Each has its own page of free questions:
The TSSA G3 practice test page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.