This is an original study aid for the Energy Manager Exam (electrical field) in Japan, organized around the four-domain outline below. According to the official application guide, the Reiwa 8 (2026) test date is August 2, applications run from April 6 to June 22 via internet application, and the listing is the 46th examination. It does not verify topic weightings, pass mark, fee, question count, statutory thresholds, or detailed assessment format, so topic scope, legal duties, and exam logistics remain subject to current official review. The MCQ sample checks supporting knowledge and is not a simulation of any official written, oral, practical, or listening task. High-yield check: S = √3 × V_LL × I_L; P = S cosφ; Q = S sinφ; motor input = output ÷ efficiency; 30-minute demand kW = interval kWh ÷ 0.5 h; load factor = average demand ÷ maximum demand; unit consumption = energy ÷ production; centrifugal pump/fan power scales approximately with speed cubed.
Credential, source boundary, and exam identity
Use the supplied page for identity and dates; use the four-domain outline only as a study map.
The official application page identifies the エネルギー管理士試験 and lists the Reiwa 8 (2026) test date as August 2, with an application window from April 6 to June 22 and internet application. It also labels the listing as the 46th examination. Treat these as administrative facts, not as evidence of topic weightings or scoring.
The same source does not state a syllabus breakdown, question count, pass mark, fee, or current statutory thresholds. This package therefore treats the four domains as an organizing outline for study, not as an official weighting. Where a duty, threshold, or format matters, verify it against the current official guide and current law; those points are subject to review.
The application guide is not a technical syllabus. It does not establish assessment methods such as item format, scoring method, or cognitive weighting. The study material therefore teaches stable electrical and management concepts without claiming that any particular question style is the current official format.
Tested skills and preparation priorities
Prioritize formula selection, unit discipline, and integrated interpretation over memorizing isolated facts.
The outline points to four interacting skill families: electrical fundamentals; equipment losses and efficiency; measurement and demand management; and management metrics with applied law-oriented reasoning. Expect study tasks that combine these: selecting a three-phase formula, converting a meter reading into demand, interpreting load factor, and explaining why an efficiency measure saves energy.
High-yield priorities are the √3 relationships for balanced three-phase circuits, active/reactive/apparent power, CT and PT ratios, 30-minute integrated demand, load factor, unit energy consumption, motor input-versus-output efficiency, transformer constant versus load losses, and fan/pump affinity laws. Legal and reporting topics should be learned as management concepts first, then checked against current sources.
The MCQ set below checks supporting knowledge and application. It is not a full mock examination and not a simulation of any official oral, practical, written, or listening task. The integrated practice section supplies representative open-task practice because such work is closer to real engineering reasoning than isolated multiple-choice recall.
Electrical fundamentals with worked checks
For balanced three-phase systems, compute apparent power first, then resolve it with the power-factor angle.
Use S = √3 × V_LL × I_L for apparent power in VA, P = S cosφ for active power, and Q = S sinφ for reactive power. For a 400 V, 50 A load at 0.80 lagging, S is about 34.6 kVA, P is about 27.7 kW, and Q is about 20.8 kvar. If you need to improve power factor, calculate the before and after reactive powers and use their difference as the capacitor rating.
For power-factor correction from 100 kW at 0.80 lagging to 0.95 lagging, Q_before = 100 × tan(acos 0.80) = 75.0 kvar and Q_after = 100 × tan(acos 0.95) ≈ 32.9 kvar. The capacitor needed is about 42.1 kvar. Always check whether the load is inductive or capacitive and whether the target is lagging or leading.
Delta and star relationships are separate from the three-phase power formula. In a balanced delta load, line current is √3 times phase current. In a star connection, line voltage is √3 times phase voltage, while line current equals phase current. A 400 V star phase voltage is about 231 V, not 400 V. If a question gives phase values, convert to line values before using S = √3 × V_LL × I_L.
Equipment systems, losses, and efficiency economics
Separate fixed losses from load-dependent losses, and use the affinity-law exponent correctly.
Transformer iron loss is approximately constant at normal voltage, while copper loss varies with current squared. If full-load copper loss is 8 kW and load falls to 50%, copper loss becomes 8 × 0.5² = 2 kW. Adding 3 kW iron loss gives 5 kW total loss. This is why part-load efficiency can peak before full load. For maximum-efficiency questions, set variable copper loss equal to constant iron loss and solve for the load fraction.
For motors, input power = output power ÷ efficiency. A 75 kW output motor at 88% efficiency draws about 85.2 kW; at 93% it draws about 80.6 kW. The input reduction is about 4.6 kW. Over 6,000 hours, the energy saving is about 27.5 MWh. This calculation supports simple payback: incremental cost divided by annual operating-cost saving.
Centrifugal pumps and fans follow the affinity laws approximately: flow varies with speed, head with speed squared, and shaft power with speed cubed. Reducing speed to 80% gives ideal power of 0.8³ = 0.512, or about 51%. At 70%, ideal power is about 34%. Actual savings depend on system curve and control, so treat the cube law as an estimate, not a guarantee.
Measurement, CT/PT ratios, demand, and load factor
Instrument ratios convert primary values to secondary values; demand is energy divided by the integration interval.
A 400/5 CT has a ratio of 80:1. A primary current of 320 A produces 4 A secondary. Never open-circuit an energized CT secondary: the CT can develop hazardous voltage. PT ratios work similarly, reducing high voltage to a safe metering level. Confirm meter and instrument ratings before connecting.
Thirty-minute integrated demand in kW equals kWh recorded in the 30-minute interval divided by 0.5 h, equivalently twice the kWh. If 18 kWh is recorded in 30 minutes, demand is 36 kW. For a month, average demand is monthly kWh divided by hours, and load factor is average demand divided by maximum demand. With 540,000 kWh over 720 hours, average demand is 750 kW; if maximum demand is 1,000 kW, load factor is 75%.
Distorted waveforms from inverter-driven equipment require true-RMS measurement for better heating-equivalent readings. Average-responding meters may mislead on harmonics. Measurement plans should match the meter to the waveform, confirm CT/PT burden, and record the integration period. A demand reading without a stated interval is ambiguous.
Energy management metrics and applied calculations
Normalize energy by production or activity, and keep demand charges separate from energy charges.
Unit energy consumption = energy consumption ÷ production volume. If a plant uses 480,000 kWh and produces 12,000 units, unit consumption is 40 kWh/unit. A fall from 42 to 40 kWh/unit while total energy rises can still mean improvement, because production may have increased faster than energy use.
Demand charges use maximum demand, not total energy. A hypothetical 800 kW maximum demand at 1,500 yen/kW/month for 12 months gives 800 × 1,500 × 12 = 14.4 million yen. The calculation is arithmetic once the tariff structure is supplied; the rate itself must come from a current tariff source.
Heat pumps convert electrical input into delivered heat using COP = heat output ÷ electrical input. At COP 4.0, 10,000 kWh of electricity delivers about 40,000 kWh of heat under the stated conditions. COP varies with temperature and operation, so do not treat one value as universal. Legal duties and reporting thresholds are not established by the supplied page; study them conceptually and verify current requirements.
Common errors and error-prevention habits
Most lost marks come from unit slips, wrong connection assumptions, and confusing efficiency definitions.
Keep kW and kWh distinct: power is instantaneous or demand over an interval; energy is power multiplied by time. For a 30-minute interval, divide kWh by 0.5, not by 1. Do not omit √3 in balanced three-phase power or line-to-phase conversions. Do not use line current where phase current is required in a delta load.
In equipment problems, check whether efficiency is given on output or input. Motor output is mechanical; input is electrical. For transformers, copper loss scales with load squared; iron loss does not. For fans and pumps, power scales with speed cubed, not squared. For CTs, use the primary-to-secondary ratio and never treat an open secondary as harmless.
On management questions, separate total energy from unit consumption and average demand from maximum demand. Do not assert a current statutory threshold unless you have checked it. Show units in every step and ask whether the answer is plausible. A quick plausibility check catches many errors before they become final answers.
Integrated practice task and self-check rubric
Complete the scenario end-to-end, then grade the method before the final number.
Practice scenario: A 6.6 kV feeder carries 100 A at 0.85 lagging. In one 30-minute interval, 450 kWh is recorded. Monthly energy is 480,000 kWh over 720 hours; maximum demand is 900 kW; production is 12,000 units. A 75 kW output motor operates 6,000 hours/year; its efficiency improves from 88% to 93%.
Calculate apparent, active, and reactive power on the feeder; the 30-minute integrated demand; monthly average demand and load factor; unit energy consumption; and annual motor input-energy saving. Then write one sentence explaining why the motor saving is an input-energy calculation, not an output-energy calculation.
Self-check rubric: (1) correct formula and unit conversion; (2) correct use of √3 and power-factor angle; (3) correct 0.5-hour demand divisor; (4) correct average-versus-maximum distinction; (5) correct production normalization; (6) correct efficiency direction; (7) plausible magnitude; (8) clear assumption note. This is representative open-task practice, not a simulation of an official oral, practical, written, or listening examination.
Practical study sequence
Build a formula sheet, drill mixed calculations, then audit errors weekly.
Weeks 1–2: master three-phase power, power factor, delta/star conversions, and voltage/current relationships. Weeks 3–4: study motors, transformers, lighting, pumps/fans, and efficiency economics. Week 5: measurement, CT/PT, demand, load factor, and true-RMS concepts. Week 6: unit consumption, demand charges, heat-pump COP, and management concepts; separately verify current legal and reporting details.
Each study block should end with three mixed problems and a written error note. Keep a one-page sheet of formulas with units and assumptions. In the final phase, attempt an integrated scenario under time, then revise only the missed mechanism. The MCQ set below checks supporting knowledge; it is not a full mock examination.
References and further reading
Use these references to explore the concepts and check the latest information from the relevant organizations.