Ten free 309A Electrician practice questions.

Ten 309A Electrician questions in the format of the Red Seal exam: four options, one correct answer, no trick questions. They are free to use, print and share. There is nothing to sign up for on this page.

01How to use these

The questions come from the TicketPrep 309A bank and are spread across the exam's work activities in the order and roughly the proportion the Red Seal Program publishes for this trade: A (performs common occupational skills), B (installs, services and maintains generating, distribution and service systems), C (installs, services and maintains wiring systems), D (installs, services and maintains motors and control systems), E (installs, services and maintains signalling and communication systems). Answer each one before opening the explanation. Every explanation covers all four options, because on the real exam the wrong options are written to be plausible, and knowing why they are wrong is most of the skill.

• Pace. The exam allows four hours for 100 questions, so about 2 min 24 s per question. Try these at that pace.
• Print. The printed version shows the questions and the answer key without the explanations, so it works as a handout. Print this page
• Mark. The pass mark is 70 percent on every Red Seal trade; seven of ten here is the same bar.

02The questions

1. Procedural · Performs common occupational skills

   An electrician must open an energized 600 V motor control centre bucket to take a current reading. The arc-flash label on the section reads 8 cal/cm² incident energy with a 1.2 m arc-flash boundary. What PPE is required for the task?

   1. Flame-resistant polyester coveralls with a standard face shield.
   2. Arc-rated clothing and face protection rated at least 8 cal/cm², plus voltage-rated gloves.
   3. Cotton coveralls and safety glasses, because the reading takes only a few seconds.
   4. Rubber insulating gloves and a hard hat; arc-rated clothing is only needed above 40 cal/cm².
   Show the answer

   B. Correct. Inside the arc-flash boundary with the door open, the worker needs arc-rated clothing and face/head protection with an arc rating at or above the labelled incident energy, plus voltage-rated rubber gloves with leather protectors for the shock hazard, safety glasses and hearing protection. CSA Z462 is the standard the RSOS names for this.

   Why not the others

   A. Polyester and other meltable synthetics are prohibited under or as arc protection because they melt onto skin. A standard (non-arc-rated) face shield offers no arc protection. Both the garment and the face protection must carry an arc rating.

   C. Duration does not reduce incident energy; an arc can occur in milliseconds. Untreated cotton is not arc-rated and can ignite. The label's 8 cal/cm² sets the minimum arc rating for the clothing.

   D. This inverts the rule. Above 40 cal/cm² energized work is normally prohibited; arc-rated clothing is required at any labelled incident energy above the threshold for everyday clothing, and 8 cal/cm² is well past it. Gloves alone address shock, not arc flash.

2. Procedural · Installs, services and maintains generating, distribution and service systems

   In a 120/240 V single-phase three-wire service, line 1 carries 40 A and line 2 carries 25 A, with all loads connected line-to-neutral. What current flows in the neutral?

   1. 65 A
   2. 40 A
   3. 15 A
   4. 25 A
   Show the answer

   C. Correct. In the Edison three-wire system the two line currents are 180° apart, so the neutral carries only the unbalance: 40 A − 25 A = 15 A. A perfectly balanced service has zero neutral current, which is why an open neutral is so dangerous: the imbalance then appears as voltage across the loads.

   Why not the others

   A. Adding the currents treats them as in phase. Across the two halves of a centre-tapped transformer they are opposite, so they subtract in the neutral.

   B. This is line 1's current. With line 2 also loaded, part of line 1's return path is through line 2, not the neutral.

   D. This is line 2's current, not the difference. The neutral never carries a full line current unless the other line is unloaded.

3. Procedural · Installs, services and maintains generating, distribution and service systems

   A panelboard is being installed in a dwelling unit. What limit does the CEC place on the height of its breaker operating handles above the finished floor?

   1. Not more than 2.0 m.
   2. Not more than 1.7 m.
   3. Not less than 1.2 m.
   4. Exactly 1.5 m to the centre of the handle.
   Show the answer

   B. Correct. Rule 26-600(2): panelboards in dwelling units are installed as high as possible, with no overcurrent device operating handle more than 1.7 m above the finished floor, so any occupant can reach the breakers in an emergency. Rule 26-600(1) also keeps panelboards out of clothes closets, bathrooms, stairways and hot or dangerous locations.

   Why not the others

   A. 2.0 m would put the handles above the reach of many occupants; the rule sets 1.7 m.

   C. There is no minimum in the rule; 'as high as possible' with a 1.7 m cap is the requirement.

   D. The CEC sets a maximum, not a fixed height; 1.5 m is acceptable but not required.

4. Critical · Installs, services and maintains generating, distribution and service systems

   A drill with a metal case faulted internally and its case became energized, but the 15 A breaker did not trip until a worker was shocked. The drill is fed through a long run of flexible metal conduit. What is the most likely reason the breaker did not trip?

   1. The drill's cord was too long, adding resistance.
   2. The breaker was defective and must be replaced.
   3. The circuit needed a GFCI, since breakers do not respond to ground faults.
   4. The bonding path was open, so the fault current was too small to trip it.
   Show the answer

   D. Correct. A breaker only trips if fault current is many times its rating, which requires a low-impedance bonding path to the source. Broken flexible conduit fittings, a missing bonding conductor or a corroded joint leave the case energized with little current flowing until a person provides a path. The RSOS names ground loop impedance testers as the tool that finds this before someone is hurt.

   Why not the others

   A. Cord resistance limits fault current slightly but not enough to prevent a 15 A breaker from tripping; an open bonding path is the difference between 200 A and near zero.

   B. A breaker cannot trip on fault current that never reaches it; the missing current is the cause, not the breaker.

   C. A breaker does respond to a solid ground fault if the bonding path is intact. A GFCI would have protected the worker, but the underlying defect is the broken bonding path.

5. Procedural · Installs, services and maintains wiring systems

   Non-metallic sheathed cable (NMD90) is being run exposed along the underside of joists in a dwelling basement. How must it be supported under the CEC?

   1. At intervals of 2 m, with no requirement near boxes.
   2. Within 1 m of each box and at intervals not exceeding 3 m.
   3. Only at the ends of the run, if it is pulled tight.
   4. Within 300 mm of each box and at intervals not exceeding 1.5 m.
   Show the answer

   D. Correct. The CEC requires non-metallic sheathed cable to be secured within 300 mm of every box or fitting and at least every 1.5 m along the run, using straps or staples that do not damage the sheath. Where run through holes in joists on centres of 1.5 m or less, the joists themselves count as support.

   Why not the others

   A. Support near the box is required so the connector is not stressed by the cable's weight or by pulling; and 2 m exceeds the interval for cable.

   B. 1 m and 3 m are the support intervals for rigid conduit and EMT, not for flexible cable, which sags and can be damaged if left unsupported that far.

   C. Cable is never installed in tension; it must be supported along its length at the required interval.

6. Procedural · Installs, services and maintains wiring systems

   Receptacles are being placed along a kitchen counter in a dwelling. What placement rule applies to the counter work surface?

   1. One receptacle per 3 m of counter.
   2. One receptacle at each end of the counter only.
   3. No point may be more than 1.8 m from a receptacle, as in other rooms.
   4. No point along the counter may be more than 900 mm from a receptacle.
   Show the answer

   D. Correct. Kitchen counter receptacles are spaced so that no point along the usable counter is more than 900 mm from a receptacle, and they are supplied by dedicated circuits (20 A T-slot or split 15 A). Counter sections behind sinks and ranges are excluded, and receptacles within 1.5 m of the sink are GFCI-protected.

   Why not the others

   A. 3 m spacing would leave much of the counter beyond appliance cord reach; the rule is 900 mm from any point.

   B. Long counters need intermediate receptacles to meet the 900 mm rule.

   C. 1.8 m is the general wall rule; counters use a tighter 900 mm spacing because of appliance cord lengths.

7. Procedural · Installs, services and maintains wiring systems

   A chiller compressor has been off for the winter. Why must its crankcase heater be energized for the manufacturer's stated period, typically 24 hours, before the compressor is started in spring?

   1. To thin the oil so the compressor starts on less current.
   2. To pre-heat the chilled water loop.
   3. To warm the motor windings so the insulation resistance is acceptable.
   4. To boil refrigerant out of the oil so the compressor does not start with liquid.
   Show the answer

   D. Correct. During a shutdown refrigerant migrates to the coldest point and dissolves in the compressor oil. On a cold start the refrigerant flashes, foams the oil out of the crankcase and can slug liquid into the compressor, wrecking valves or scrolls. The crankcase heater warms the oil and boils the refrigerant off. The RSOS lists chiller heaters among HVAC systems the electrician connects.

   Why not the others

   A. Starting current is set by the motor, not oil viscosity.

   B. The heater is a small element on the compressor casing; it does nothing for the water loop.

   C. Winding warmth is a side effect; the purpose is refrigerant migration control.

8. Critical · Installs, services and maintains motors and control systems

   A three-phase motor's nameplate shows a full-load current of 14 A and a service factor of 1.15. Under the CEC motor rules, what is the maximum setting or rating of its running overload protection?

   1. 14 A
   2. 21 A
   3. 17.5 A
   4. 16.1 A
   Show the answer

   C. Correct. Rule 28-306(1): overload devices are selected or set to trip at not more than 125 % of the motor's full load current rating for a motor with a marked service factor of 1.15 or greater, and 115 % where there is no marked service factor or it is less than 1.15; 14 × 1.25 = 17.5 A. The RSOS lists FLC and service factor among the nameplate data used to install starters.

   Why not the others

   A. Setting the overload exactly at full-load current would nuisance-trip on normal load fluctuations; the code allows a margin.

   B. 150 % is not a CEC overload limit; it would allow the motor to run far above its rating.

   D. 16.1 A is 115 % of FLA, the limit for motors with no marked service factor or one below 1.15. This motor is marked 1.15.

9. Recall · Installs, services and maintains motors and control systems

   How does a DC drive increase a shunt motor's speed above its base (rated) speed?

   1. By increasing the field current.
   2. By weakening the field at rated armature voltage.
   3. By raising the armature voltage above the motor's rating.
   4. By switching the motor to a series connection.
   Show the answer

   B. Correct. Below base speed the drive varies armature voltage with full field; at rated armature voltage the motor is at base speed. Reducing the field current raises speed further, at reduced torque (constant horsepower). The RSOS lists field components, speed and torque controls among DC drive components.

   Why not the others

   A. More field current slows a DC motor; the speed relationship is inverse to field flux.

   C. Over-voltaging the armature damages the commutator and insulation and is not how drives extend speed.

   D. Motor connection is fixed; the drive controls speed electrically.

10. Procedural · Installs, services and maintains signalling and communication systems

    A conventional (non-addressable) fire alarm system uses Class B initiating circuits. Where must the end-of-line resistor for each circuit be installed?

    1. In the fire alarm panel, on the circuit's terminals.
    2. At the first device from the panel.
    3. At the electrically last device on the circuit.
    4. Anywhere, since the panel only needs to see the resistance value.
    Show the answer

    C. Correct. The panel supervises a Class B circuit by monitoring the current through the end-of-line resistor; an open anywhere on the circuit removes the resistor from the path and produces a trouble signal. If the resistor sits in the panel, an open circuit goes undetected and the devices beyond it are silently disconnected. The RSOS lists end-of-line devices among fire alarm components and Class A and Class B among system types.

    Why not the others

    A. A resistor in the panel supervises nothing beyond the panel terminals; any open in the field wiring is invisible.

    B. Supervision covers only the wiring up to the resistor; at the first device the rest of the circuit is unsupervised.

    D. The panel sees the value, but the point is what lies between the panel and the resistor; only the last device covers the whole circuit.

03Answer key

04More free questions

The same format for the other five trades, plus the free guides on the pass mark, question counts, exam day and how to study.

How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.