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Safety Management of Private Electrical Installations and Electrical Laws

Class 1 Electrician 第一種電気工事士 (written exam) · 第一種電気工事士(学科試験) · Written by Tokutei Pass based on the official study texts; not copied verbatim.

Electricians Act 1: Scope of Work for First-Class Electricians and Special Electrical Work

Under the Electricians Act (電気工事士法), the scope of electrical work that a First-Class Electrician (第一種電気工事士) license holder may perform covers general electrical installations (一般用電気工作物等 — residences and small shops receiving low voltage at 600V or less) and private electrical installations (自家用電気工作物) with a maximum power of under 500kW (excluding special electrical work).

Conversely, electrical work on private electrical installations with a maximum power of 500kW or more, or electric utility installations (電気事業用電気工作物) such as power plants, substations, and transmission lines, falls outside the scope of the Electricians Act (under the safety supervision of a Chief Electrical Engineer 電気主任技術者), so work may be performed without an electrician's license.

Even within private electrical installations under 500kW, two categories are designated as special electrical work (特殊電気工事): neon work (ネオン工事 — work on neon distribution boards, neon transformers, and neon tubes) and emergency standby generator work (非常用予備発電装置工事).

This special electrical work cannot be performed with only a First-Class Electrician license; it requires a Special Electrical Work Qualifier (特種電気工事資格者) certificate for the respective field. On the exam, the most frequent wrong choice states that a First-Class Electrician performed emergency standby generator work.

Additionally, within private installations under 500kW, work on low-voltage sections operating at 600V or less (excluding outdoor power lines and special electrical work) is called simple electrical work (簡易電気工事), which may be performed by someone holding a Certified Electrical Work Worker (認定電気工事従事者) certificate.

Electricians Act 1: Scope of Work for First-Class Electricians and Special Electrical Work

Key points


  • Scope of work for a First-Class Electrician: General electrical installations + Private electrical installations with maximum power under 500kW (excluding special electrical work)

  • No electrician license is required for private electrical installations of 500kW or more, or for power stations and utility substations

  • Special electrical work (neon work and emergency standby generator work) can only be performed by a Special Electrical Work Qualifier (特種電気工事資格者); a First-Class license alone is not enough

  • Simple electrical work (low-voltage sections ≤ 600V excluding power lines in private installations < 500kW) can also be performed by a Certified Electrical Work Worker (認定電気工事従事者)
WordMeaning
自家用電気工作物 (500kW未満): Private electrical installation (maximum power under 500kW)
特殊電気工事 (ネオン・非常用予備発電): Special electrical work (Neon and Emergency generator)
特種電気工事資格者: Special Electrical Work Qualifier
簡易電気工事・認定電気工事従事者: Simple electrical work and Certified Electrical Work Worker

Electricians Act 2: 3 Years Practical Experience for License, Periodic Training, and Minor Work

Passing the First-Class Electrician exam does not immediately grant a license (免状). To receive the license from the prefectural governor, at least 3 years of practical experience in electrical work is required, whether gained before or after passing the exam (immediately after passing, one can apply to become a Certified Electrical Work Worker 認定電気工事従事者 to accumulate practical experience).

Excluded from this 3-year practical experience requirement are four types of work: (1) Minor work (軽微な工事); (2) Special electrical work (neon and emergency standby generators); (3) Overhead power line work at 50,000V or higher; and (4) Safety communication equipment work. Exam questions frequently try to trap you by counting emergency standby generator work experience toward the 3 years.

To maintain up-to-date safety knowledge and skills for private electrical installations, a First-Class Electrician is obligated to attend periodic training (定期講習) conducted by an organization designated by the Minister of Economy, Trade and Industry at least once every 5 years from the date the license was issued (or the date of the previous training). Second-Class Electricians have no periodic training obligation.

When a name change occurs, an application for license rewriting (免状の書換え申請) must be submitted to the prefectural governor, and if the license is damaged or lost, an application for reissuance (再交付申請) must be made (an address change alone does not require rewriting). The license must always be carried while working.

Minor work (軽微な工事) that anyone can do without a license includes connecting cords to plug-in or screw-in connectors at 600V or less, replacing fuses, secondary wiring (36V or less) for bells and intercoms, and installing watt-hour meters or grounding electrodes. Minor tasks (軽微な作業) that unlicensed persons can perform under on-site supervision by an electrician include mounting conduits, ducts, and racks.

Key points


  • Issuance of a First-Class license requires at least 3 years of practical experience (after passing the exam, one can immediately become a Certified Electrical Work Worker without prior experience)

  • Four works excluded from practical experience: Minor work, Special electrical work, Overhead lines ≥ 50,000V, and Safety communication equipment work

  • A First-Class Electrician must take periodic training (定期講習) once within every 5 years from the license issue date (or previous training date)

  • An application to rewrite the license (書換え申請) is required for a name change, but is not required for an address change
WordMeaning
実務経験 (3年以上): Practical work experience (3 years or more)
定期講習 (5年以内ごと): Periodic training (once within every 5 years for First-Class)
軽微な工事・軽微な作業: Minor work (unlicensed) and Minor tasks (supervised)
免状の書換え・再交付: Rewriting and Reissuance of an electrician license

Electricity Business Act (Small-Output Generation, Accident Reports) and Electrical Appliance Safety Act

Under the Electricity Business Act (電気事業法), since the March 2023 amendment the output limits for small-output power generation facilities (小出力発電設備, connected to low-voltage installations) are: solar PV under 10kW; hydro under 20kW; internal combustion (diesel, etc.) and fuel cells under 10kW; with the total on the same premises under 50kW. Solar PV of 10kW to under 50kW and wind under 20kW are now Small-scale Electrical Facilities for Business Use (小規模事業用電気工作物).

Factories and buildings receiving high voltage (such as 6,600V) or solar power plants of 50kW or more are classified as private electrical installations (自家用電気工作物). The owner is obligated to establish and file Safety Regulations (保安規程) and to appoint (or outsource) and file a Chief Electrical Engineer (電気主任技術者).

If an electric shock fatality/injury, electrical fire, damage to major electrical equipment, or fault propagation disrupting utility supply (波及事故) occurs at a private electrical installation, the owner must submit a preliminary report (速報) within 24 hours of learning of the accident, and a detailed report (詳報) within 30 days of the accident occurrence to the Director of the Regional Industrial Safety and Inspection Department.

Under the Electrical Appliance and Material Safety Act (電気用品安全法), Specified Electrical Appliances (特定電気用品) with a higher hazard risk bear a diamond-shaped <PS>E (◇PSE) mark, while other electrical appliances bear a circular (PS)E (〇PSE) mark. Appliances without a PSE mark are prohibited from sale or use in electrical construction.

Examples of Specified Electrical Appliances (◇PSE) include circuit breakers (100A or less), switches, outlets, time switches, insulated wires such as IV (100mm² or less), and VVF/VVR cables (22mm² or less). Conversely, conduits (metal, CD and PF), ventilation fans, LED lamps, electromagnetic switches, and cables over 22mm² (such as 38mm²) carry the circular 〇PSE mark.

Key points


  • Small-output generation limits: solar PV < 10kW, hydro < 20kW, internal combustion (diesel) < 10kW (total on premises < 50kW). Solar 10–50kW and wind < 20kW are Small-scale Electrical Facilities for Business Use

  • Owners of private electrical installations must file Safety Regulations and appoint a Chief Electrical Engineer. Electrical accident reports: preliminary within 24 hours, detailed within 30 days

  • Specified Electrical Appliances (◇PSE): circuit breakers (≤ 100A), time switches, outlets, IV wires ≤ 100mm², VVF cables ≤ 22mm²

  • Non-Specified Electrical Appliances (〇PSE): thick cables over 22mm² (e.g., 38mm²), metal conduits, CD / PF conduits, electromagnetic switches, covered knife switches, LED lamps, ventilation fans
WordMeaning
小出力発電設備 (太陽10kW・水力20kW・内燃10kW未満): Small-output power generation equipment
保安規程・電気主任技術者: Safety Regulations and Chief Electrical Engineer
電気関係報告規則 (24時間・30日): Electricity-Related Reporting Rules (24 hours / 30 days)
特定電気用品 (◇PSE): Specified Electrical Appliances (diamond PSE mark)

Electrical Construction Business Act (Chief Electrician and Required Measuring Instruments)

The Electrical Construction Business Act (電気工事業法) classifies contractors into four categories based on the installations handled and whether they hold a construction business permit. Those performing general (and private) electrical work are Registered Electrical Contractors (登録電気工事業者, renewed every 5 years); those with a construction business permit are Deemed Registered Electrical Contractors (みなし登録電気工事業者).

Conversely, contractors performing work only on private electrical installations (under 500kW) file a notification at least 10 days before starting business as Notified Electrical Contractors (通知電気工事業者; or Deemed Notified Electrical Contractors if holding a construction permit). Because they do not work on general electrical installations, they are not required to appoint a Chief Electrician (主任電気工事士).

Registered and Deemed Registered Electrical Contractors who perform work on general electrical installations must appoint a Chief Electrician (主任電気工事士) at each business office. Only two qualifications can serve as Chief Electrician: (1) a First-Class Electrician, or (2) a Second-Class Electrician with at least 3 years of practical experience after receiving the license. Neither a Chief Electrical Engineer (電気主任技術者) nor a Certified Electrical Work Worker can serve as Chief Electrician.

The measuring instruments that must be kept at a business office handling only general electrical installations are three items: (1) an insulation resistance tester (Megger); (2) an earth resistance tester; and (3) a circuit tester (multimeter) capable of measuring resistance and AC voltage.

In contrast, a business office that also performs work on private electrical installations must keep a total of seven items by adding four more to the three above: (4) a low-voltage voltage detector; (5) a high-voltage voltage detector; (6) a protective relay test set (継電器試験装置); and (7) a dielectric strength test set (絶縁耐力試験装置) (items 6 and 7 may be borrowed when needed). Tachometers, lux meters, sound level meters, power factor meters, and clamp meters are not required.

Electrical Construction Business Act (Chief Electrician and Required Measuring Instruments)

Key points


  • Qualifications for Chief Electrician (主任電気工事士): First-Class Electrician, or Second-Class Electrician with ≥ 3 years experience after license issuance (Chief Electrical Engineer 電気主任技術者 is not eligible!)

  • Notified / Deemed Notified Electrical Contractors handling only private electrical installations are not required to appoint a Chief Electrician

  • 7 required instruments for offices performing private electrical work: Insulation tester, Earth tester, Circuit tester, LV detector, HV detector, Relay test set, Dielectric strength test set

  • Instruments not required (wrong choices): Tachometer (回転計), Illuminance meter (照度計), Sound level meter, Power factor meter, Watt-hour meter
WordMeaning
登録電気工事業者・通知電気工事業者: Registered vs Notified Electrical Contractor
主任電気工事士 (しゅにんでんきこうじし): Chief Electrician (at a contractor's office)
継電器試験装置・絶縁耐力試験装置: Protective relay test set and Dielectric strength test set
低圧検電器・高圧検電器: Low-voltage and High-voltage voltage detectors

Technical Standards for Electrical Equipment (Voltage Classes, LV Insulation Resistance) and Exam System

Voltage classifications under the Ministerial Ordinance Establishing Technical Standards for Electrical Equipment are: (1) Low Voltage (低圧): DC 750V or less and AC 600V or less; (2) High Voltage (高圧): over DC 750V / over AC 600V up to 7,000V or less; and (3) Extra-High Voltage (特別高圧): over 7,000V for both DC and AC.

Minimum insulation resistance values for low-voltage circuits are set in three tiers: (1) Voltage to ground 150V or less (single-phase 100V, single-phase 3-wire 100/200V, etc.) requires 0.1MΩ or more; (2) Working voltage 300V or less with voltage to ground over 150V (3-phase 200V, etc.) requires 0.2MΩ or more; and (3) Working voltage over 300V (3-phase 400V, etc.) requires 0.4MΩ or more.

Make sure to remember that the standard insulation resistance values are only 0.1MΩ, 0.2MΩ, and 0.4MΩ; a standard value of 0.3MΩ does not exist. Also, when judging low-voltage circuit insulation by leakage current, the limit is 1mA or less regardless of working voltage.

High-voltage and extra-high-voltage equipment must be installed so that unauthorized persons cannot easily touch them. Furthermore, a transformer coupling a high-voltage circuit and a low-voltage circuit must always be given Class B grounding (B種接地工事) on its low-voltage neutral point (or one terminal) to prevent danger from high-to-low-voltage contact.

In addition to paper-based testing, CBT (Computer-Based Testing) has been introduced for the First-Class Electrician written exam. Standard exam questions do not include furigana readings on kanji, but foreign candidates who submit a Support Measure Application (援助措置申請 — exam with furigana) beforehand and receive approval can take the exam with furigana.

Key points


  • Voltage classes: Low Voltage = DC ≤ 750V, AC ≤ 600V; High Voltage = ≤ 7,000V; Extra-High Voltage = > 7,000V

  • Low-voltage insulation resistance: ≤ 150V to ground = ≥ 0.1MΩ; ≤ 300V (> 150V to ground) = ≥ 0.2MΩ; > 300V = ≥ 0.4MΩ (there is no 0.3MΩ!)

  • The low-voltage side of a transformer coupling high voltage and low voltage must always receive Class B grounding to prevent HV/LV contact

  • Foreign examinees wishing to take the exam with furigana readings must submit a Support Measure Application (援助措置申請) to the exam center before applying
WordMeaning
低圧・高圧・特別高圧: Low voltage (DC≤750V/AC≤600V), High voltage (≤7,000V), Extra-high voltage (>7,000V)
絶縁抵抗値 (0.1MΩ・0.2MΩ・0.4MΩ): Minimum LV insulation resistance values
高低圧混触防止 (B種接地): High/low-voltage contact prevention (Class B grounding)
CBT方式・援助措置申請: Computer-Based Testing (CBT) and Support Measure Application

Key Exam Points and Memory Tricks

Memorize all legal time periods together: (1) Practical experience for First-Class license = 3 years or more; (2) Practical experience for Second-Class to become Chief Electrician = 3 years or more after license; (3) First-Class periodic training = once within every 5 years; (4) Registered contractor renewal = 5 years; (5) Electrical accident report = preliminary within 24 hours, detailed within 30 days.

The three big qualification traps are: (1) Emergency standby generator and neon work require a Special Electrical Work Qualifier (a First-Class license alone is insufficient, and the work does not count toward the 3-year experience); (2) Private installations of 500kW or more do not require an electrician license; (3) A Chief Electrical Engineer (電気主任技術者) cannot become a Chief Electrician (主任電気工事士), and notified contractors do not need a Chief Electrician.

The 7 required measuring instruments are: Insulation tester, Earth tester, Circuit tester (the 3 for general work) + LV detector, HV detector, Relay test set, and Dielectric strength test set. Tachometers (回転計), lux meters (照度計), and power factor meters (力率計) are not required.

Numbers for small-output generation: solar < 10kW, hydro < 20kW, internal combustion (diesel) < 10kW (the 2023 amendment changed them from solar 50kW and wind 20kW). Low-voltage insulation resistance: ≤ 150V = 0.1MΩ, ≤ 300V = 0.2MΩ, > 300V = 0.4MΩ (0.3MΩ does not exist).

Key points


  • Time periods: First-Class license experience = 3 years; First-Class periodic training = within every 5 years; Accident reports = 24 hours preliminary, 30 days detailed

  • Neon & Emergency generator work = requires Special Electrical Work Qualifier (excluded from 3-year experience). ≥ 500kW = no electrician license required

  • A Chief Electrical Engineer cannot serve as Chief Electrician. The 7 required instruments do not include tachometers, lux meters, or power factor meters

  • Small-output generation = solar 10kW, hydro 20kW, diesel 10kW. LV insulation resistance = 0.1MΩ, 0.2MΩ, 0.4MΩ (0.3MΩ is fake)
WordMeaning
実務経験3年・定期講習5年: 3 years practical experience and 5-year periodic training
備え付け測定器具 (7品目): 7 required measuring instruments for private electrical work offices
特定電気用品 (◇PSE・絶縁電線100mm²以下・ケーブル22mm²以下・遮断器100A以下): Specified Electrical Appliances (insulated wires ≤ 100mm², cables ≤ 22mm², breakers ≤ 100A)

Electrical Safety Laws

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Official references

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