This knowledge preview covers the Japanese 第一種電気工事士 (First-Class Electrician) credential, which has written and practical components. It is for supporting knowledge only: the 20 questions are not a simulation of the practical examination or a substitute for the current official application guide. Written topics may include electrical fundamentals, distribution and wiring design, applications, equipment and materials, construction, inspection, diagrams, generation/transmission/substation basics, and safety law; the practical component involves completing a wiring-diagram problem with exam-provided materials and your own tools within a time limit. Because official information differs by year and schedule, verify the precise legal boundary, current work scope, availability, dates, fees, topic weightings, pass mark, and examination mode against the latest official application guide. Build the core in this order: safe isolation and verification, circuit calculation, control-diagram tracing, instrument reasoning, then regulations and practical routine. Practise short written explanations and supervised de-energized tasks; use the 20 MCQs as a knowledge check, not as a practical simulation.
Scope and Credential Identity
This is a focused Japanese First-Class Electrician study package that separates supplied-source facts from details that may have changed.
The credential is the Japanese 第一種電気工事士, not a generic national electrical licence. The examination-center overview describes an assessment of the knowledge and skills needed for the safety of private electrical installations. One supplied leaflet heading places the work family around private installations below 500 kW and contrasts this with general-use installations such as homes and small shops. Because the leaflets are different vintages, treat the precise legal boundary, current work scope, and jurisdiction as subject review.
The written component uses four-option questions and has been offered in both mark-sheet and CBT formats. After you pass the written component—or if you are exempt—you can take the practical component, where you complete a wiring-diagram problem with exam-provided materials and your own tools within a set time. Do not assume pass marks, topic weightings, fees, dates, or current availability; confirm these in the latest official application guide.
The scope note matters because a candidate can waste time memorising an old schedule or an unverified legal boundary. Use the latest official application guide for current logistics and legal scope. Use this package for the stable technical core: circuit relationships, control logic, measurement reasoning, and safety judgment.
What the Written and Practical Components Test
The written test checks broad electrical knowledge, while the practical test checks hands-on completion of a diagram-specified task.
In the supplied subject list, the written test spans electrical fundamentals; distribution theory and wiring design; electrical applications; equipment, batteries, wiring devices, materials, tools and receiving equipment; construction methods; inspection of private installations; wiring diagrams; basic generation, transmission and substation structure and characteristics; and safety law for installations. That list describes domains, not a fixed weighting. Do not infer that one subject is worth more marks because it appears earlier or has a longer description.
The practical component is not a written quiz. Be prepared to perform tasks such as wire connection, wiring work, installation of equipment, batteries and wiring devices, use of equipment and materials, cord and cabtyre cable attachment, grounding work, measurement, inspection, and operation or fault repair. You work from a given wiring diagram, using exam-provided materials and your own tools, within a time limit.
A multiple-choice set can check supporting knowledge, but it cannot check termination quality, tool control, layout, time management, or the ability to produce a compliant physical assembly. The 20 questions below are therefore a knowledge and application preview, not a simulation of the practical examination.
A Sensible Preparation Priority
Prioritise safety and circuit mechanisms first, then diagram tracing, measurement, and regulatory detail.
Start with safety because an error there has the highest consequence, not because a weighting is known. Learn to explain de-energizing, isolation, lock/tag practice in principle, verification of absence of voltage, and recognition of shock versus arc hazards. A candidate who cannot explain these clearly is not ready to discuss servicing.
Next, secure circuit fundamentals: Ohm's law, series and parallel reduction, AC RMS versus peak, balanced three-phase apparent power, and power factor. These topics support other areas: a wiring-design question may hide a simple calculation, and a measurement question may require understanding what a reading represents.
Then build diagram fluency: trace from the supply through protective devices and control elements to the coil and return. After that, study instrument selection and interpretation, followed by safety-law vocabulary and practical routine. Do not prioritise by guessed marks—no official topic weighting is stated. Adjust the sequence to your own error log, but keep safety and circuit foundations near the front.
Circuit and Power Mechanisms with Worked Examples
Write the relationship, substitute carefully, and check units and physical limits.
For a series circuit, resistance adds and current is common. A 100 V source across 20 Ω and 30 Ω in series gives R_total = 50 Ω and I = 100/50 = 2 A. The voltage drops are 20 × 2 = 40 V and 30 × 2 = 60 V; they sum to 100 V. Total power is 100 × 2 = 200 W, or 40 × 2 + 60 × 2 = 200 W. If the drops do not sum to the source voltage, the work is inconsistent.
For parallel branches, voltage is common and currents add. A 12 V source across 4 Ω and 6 Ω gives 1/R = 1/4 + 1/6 = 5/12, so R = 12/5 = 2.4 Ω. Total current is 12/2.4 = 5 A. The branch currents are 12/4 = 3 A and 12/6 = 2 A, which satisfy Kirchhoff's current law. A common mistake is to add parallel resistances directly.
For sinusoidal AC, RMS is the value used for average power in a resistive load. A peak of 141 V gives RMS ≈ 141/√2 ≈ 100 V. For a balanced three-phase load with 200 V line voltage, 20 A line current, and power factor 0.8, apparent power S = √3 × 200 × 20 ≈ 6.93 kVA. Real power P = S × 0.8 ≈ 5.54 kW. Use line values with the √3 formula only when the question supplies line quantities; do not silently mix line and phase values.
Control Wiring and Diagram Reasoning
Trace the actual path to the coil and identify which contacts must be series or parallel for the intended behaviour.
A basic motor-control ladder has a supply, a protective device, a stop circuit, a start circuit, the contactor coil, and a return path. A normally closed stop contact is usually in series with the coil so pressing stop opens the circuit. A normally closed overload contact is also in series so a sustained overload drops the coil. The start button is momentary; a contactor auxiliary contact in parallel with the start button provides self-holding, often called seal-in.
Press start: the coil energizes, the seal-in contact closes, and the coil remains energized after start is released. Press stop: the series path opens, the coil drops, and the seal-in opens. If the motor starts but drops immediately when start is released, suspect a missing seal-in or an auxiliary contact wired in series instead of parallel.
For two contactors that must not energize together, place a normally closed auxiliary contact of contactor B in series with coil A, and the reciprocal contact of A in series with coil B. This is a direct electrical interlock. Labels alone are not proof: trace terminal numbers and wire numbers through the diagram. A common error is to rely on a normally open auxiliary contact or a parallel path, which can permit both coils to energize.
Inspection and Measurement: Safe Interpretation
Select the instrument for the quantity, isolate before resistance or insulation testing, and interpret readings as evidence rather than proof.
Perform insulation resistance testing on a de-energized, isolated circuit with an appropriate megohmmeter. Consider stored energy and discharge it according to safe practice before and after testing. A low reading may indicate moisture, contamination, damage, or a connected parallel path. Do not invent a universal acceptance threshold for every circuit; stop, investigate, and follow the applicable standard or your supervisor's direction.
Earth resistance can be measured by a fall-of-potential method using auxiliary potential and current stakes. A clamp meter measures current by surrounding a conductor; if it surrounds both line and neutral of a single-phase load, the opposite currents largely cancel and the reading is near zero. Continuity and resistance measurements require a de-energized circuit and a checked meter.
Record the instrument, range, leads, and conditions. Repeat a suspicious reading rather than forcing it into the expected answer. Common errors include testing live, using current mode for voltage, failing to verify lead continuity, clamping the whole cable instead of one conductor, and treating a single low insulation reading as conclusive without checking connections and conditions.
Safety, Regulations and Practical Judgment
Treat absence of voltage as a test result, not as an assumption, and use protective equipment as support for isolation rather than a substitute.
A sound servicing sequence in principle is de-energize, isolate, apply lock/tag control, and verify absence of voltage at the point of work. Consider stored energy and adjacent live parts. Shock protection and arc-flash protection are related but not identical. Insulated tools and appropriate personal protective equipment reduce exposure, but they do not replace isolation and verification.
Practical judgment includes ladder placement away from overhead conductors, maintaining safe distances, using barriers, keeping access and walkways clear, and communicating before energization. If a conductor expected to be isolated is found live, stop work, isolate and verify, report the condition, and reassess. Continuing because the task is nearly finished is a classic safety error.
The supplied examination scope includes safety law for general-use and private installations, but this guide does not provide a complete legal rulebook. Use the current official text, the current application guide, and employer procedures. The legal boundary and installation classification should be treated as subject review, especially where source leaflets differ in date and framing.
Common Errors and How to Avoid Them
Most lost marks come from boundary errors: mixing series and parallel, confusing start and stop logic, and skipping verification.
In calculations, check whether quantities are series or parallel, whether a value is peak or RMS, whether a three-phase question gives line or phase values, and whether power factor relates real power to apparent power. Carry units and ask whether the result is physically plausible. In a series or single-loop circuit, current should equal source voltage divided by total series resistance. In a parallel circuit, total current is the sum of branch currents and can legitimately exceed the current in any one branch, so do not treat the smallest branch resistance as an overall upper bound.
In diagrams, identify normally open and normally closed contacts from the actual symbol or label, not from the device name. Verify that stop and overload contacts are in series with the coil, and that seal-in is parallel with the start button. Confirm interlocks in both directions. Do not bypass a protective contact to make a circuit work on paper.
In measurement and safety, do not test resistance on a live circuit, do not assume a non-contact tester is the only verification, and do not treat PPE as permission to work live. Keep an error log with the reason for each mistake: concept, unit, terminal, or procedure. Re-test that reason with a fresh problem.
Integrated Practice Task and Self-Check Rubric
Use a paper-based, de-energized scenario to combine tracing, calculation, measurement reasoning, and safety explanation.
Create your own study sketch, not an official sample: a 200 V three-phase motor feeder with a circuit breaker, contactor, start and stop buttons, seal-in auxiliary contact, overload relay, and grounded enclosure. On paper, trace the control path from supply to coil and back. Write a safe isolation sequence in principle. Calculate apparent and real power at 15 A line current and power factor 0.85: S = √3 × 200 × 15 ≈ 5.20 kVA; P = 5.20 × 0.85 ≈ 4.42 kW. Describe how you would set up an insulation resistance test on an isolated conductor and explain why one reading alone does not prove the whole installation is safe. Finally, list three plausible defects: missing seal-in, overload contact bypassed, and stop contact wired in parallel with the coil.
Score five criteria from 0 to 2: safety sequence and verification; circuit and control tracing; calculation accuracy with units; measurement rationale and instrument choice; defect explanation and terminology. A total of 8 or more is a signal to review remaining gaps, not a prediction of examination success. This is not an official pass standard and not a substitute for supervised practical training.
Study Sequence and Exam-Day Discipline
Use a repeating cycle of recall, calculation, tracing, measurement reasoning, and short written explanation.
A practical six-cycle sequence is: circuit fundamentals; AC RMS and balanced three-phase power; control and single-line diagrams; inspection and instruments; safety and legal vocabulary; integrated review. In each cycle, spend a short block on recall, a short block on numerical work, and a short block on diagram tracing. Keep a one-page error log and revisit it weekly. This is a study plan, not a claim about required hours or outcomes.
For daily work, use a 30-minute pattern: five minutes of recall from memory, ten minutes of calculation, ten minutes of tracing or measurement interpretation, and five minutes writing one explanation in plain language. Once a week, complete the integrated paper task above. For practical preparation, use only supervised, de-energized practice that follows your instructor's safety rules and the applicable regulations.
On a written test, read the stem before the options, eliminate physically impossible answers, and check units and terminal references. On a practical task, follow the given instructions, organise materials, work to the diagram, inspect your own terminations and grounding, and leave time for a final check. If a rule, date, fee, or availability detail is uncertain, consult the latest official information rather than an old leaflet or this guide.
References and further reading
Use these references to explore the concepts and check the latest information from the relevant organizations.