Electrical Machines and Wiring Devices

Ns = 120f / p = 120 × 50 / 4 = 1500 min⁻¹. 1800 is the value for 4 poles at 60 Hz, 3000 for 2 poles at 50 Hz, and 1200 for 6 poles at 60 Hz.

Article 33(3) and Table 33-2 require a circuit breaker rated 30 A or less to trip within 60 minutes at 1.25 times and within 2 minutes at 2 times its rated current. The option "within 60 minutes at 1 times" is wrong: it must NOT trip automatically at 1 times its rated current. The option "within 2 minutes at 1.25 times" mixes up the times for 1.25 times (60 minutes) and 2 times (2 minutes). The option "within 60 minutes at 2 times" is too slow: at 2 times it must trip within 2 minutes.

s = (Ns − N) / Ns = (1800 − 1746) / 1800 = 54 / 1800 = 0.03 = 3%. 54 is the speed difference, not a ratio. 97% is N / Ns, the opposite of slip. 5% is a calculation error.

Ns = 120 × 60 / 4 = 1800. N = 1800 × (1 − 0.04) = 1728 min⁻¹. 1800 is the synchronous speed itself, 1872 wrongly adds the slip, and 1440 applies the slip to the 50 Hz synchronous speed of 1500.

Synchronous speed is proportional to frequency: 60 / 50 = 1.2. With similar slip, the speed also becomes about 1.2 times. 0.83 is the reverse direction, 1.44 wrongly squares 1.2, and speed does change with frequency even if the number of poles is the same.

Swapping two wires reverses the phase sequence, so the rotating magnetic field turns the other way. Shifting all three keeps the same phase sequence. Lowering the voltage changes speed or torque, not direction. A power-factor capacitor (進相コンデンサ) improves power factor and has nothing to do with direction.

In star, each winding voltage is 1/√3, so the winding current is 1/√3. In delta, the line current is √3 times the winding current, but in star they are equal. So (1/√3) ÷ √3 = 1/3. 1/√3 looks only at one winding; √3 and 3 go in the wrong direction.

In star the voltage is lower, so starting current drops to 1/3; torque is proportional to voltage squared, so starting torque also drops to 1/3. It does not increase torque. After speeding up, the motor is switched to delta. It switches windings between star and delta, so it is used for three-phase motors.

The capacitor is connected in parallel with the motor. It cancels the lagging current, raises the power factor and reduces the current in the wires. It is not in series. The frame-to-earth connection is the grounding wire's job. A thermal relay provides overload protection, which a capacitor cannot replace.

Article 65 excludes motors with an output of 0.2 kW or less, not 2 kW. There is no exclusion based on voltage (three-phase 200 V or single-phase 100 V).

A magnetic switch combines a magnetic contactor (電磁接触器), which opens and closes contacts with an electromagnet, and a thermal overload relay (熱動継電器), which detects overload current by heat. The breakers belong in the distribution board, the capacitor improves power factor, and the timer and automatic switch control lighting.

The Measurement Units Order (計量単位令) defines lux as the illuminance when a 1 m² surface is lit by 1 lm of luminous flux. Light strength in a direction is luminous intensity (cd), flux per watt is luminous efficacy (lm/W), and energy is in watts or joules, not lux.

Article 36(1)(ii)(b) makes an exception for equipment installed in a dry place. The option "100 V to earth in a place exposed to water" is wrong: the exception for 150 V or less to earth applies only to places other than those exposed to water. The option "200 V to earth in a damp place" is not a dry place, and the voltage to earth is over 150 V. The option "Class D earthing of 100 Ω" is wrong: the earthing exception requires a Class C or D earthing resistance of 3 Ω or less.

E = I / r² = 360 / 3² = 360 / 9 = 40 lx. 120 divides without squaring the distance, 1080 multiplies by the distance, and 3240 multiplies by the distance squared.

Article 153(iii) makes an exception for a single-phase motor whose supply-side overcurrent device is rated 15 A or less (20 A or less for a circuit breaker). For the option with a three-phase motor, the exception does not apply because the motor is three-phase. The option "2 kW or less" is wrong: the output exception is 0.2 kW or less. The option about an operator checking from time to time is wrong: the exception is for a motor placed where an operator can watch it at all times while it runs.

A fluorescent lamp makes ultraviolet light by a discharge in mercury vapour, and the phosphor (蛍光体) inside the tube turns it into visible light. Heating a filament is an incandescent bulb, halogen gas is a halogen bulb, and a semiconductor is how an LED works.

A discharge lets more current flow as current increases, so the ballast limits the current. AC-to-DC power circuits are a feature of LED fixtures, cutting the circuit on leakage is an earth leakage breaker, and switching on in the dark is an automatic light switch.

An inverter-type lamp uses an electronic circuit to raise the frequency above mains frequency (50/60 Hz), so it flickers less, is more efficient and lights quickly. Slow lighting and more flicker are the opposite of the comparison. Lighting at mains frequency is not the inverter type.

An LED is a semiconductor light-emitting element with high efficacy and no mercury. Filaments are in incandescent bulbs, and mercury vapour is used in fluorescent lamps. LEDs light on DC, so the fixture contains a power circuit that converts AC to DC.

The Ministry explains that only manufacture and import/export are banned; use, sale and purchase are not. Straight tubes are banned from 1 January 2028 (from 1 January 2027 for those using mainly halophosphate phosphor), not 2026. Bulb-type lamps are covered from 1 January 2026 (over 30 W from 1 January 2027).

Place two 3-way switches (3路スイッチ) at the ends and (3 − 2) = 1 four-way switch (4路スイッチ) between them. Three 3-way switches alone cannot do it. A 4-way switch is not used at the ends. Three single-pole switches do not let each place turn the light on and off independently.

You need two 3-way switches plus (n − 2) 4-way switches. With n = 4, that is two 4-way switches. One is for three places; three or four wrongly assume no 3-way switches are used.

The locator lamp is connected in parallel with the switch contacts, so it lights when the contacts are open (off) and shows where the switch is in the dark. A lamp that lights when on is a pilot (confirmation) lamp (確認表示灯). It does not signal overcurrent or leakage.

A pilot lamp (確認表示灯) is in parallel with the load and lights while the switch is on and the load is running. A locator lamp lights when off, so it cannot show operation. A 4-way switch is for switching from three or more places, and an automatic light switch turns on and off by brightness.

An automatic light switch senses the surrounding brightness: it turns on in the dark and off in daylight, and is used for outdoor lights. Turning off after a set time is a timer switch, changing brightness is a dimmer, and turning on when someone approaches is a motion-sensor device, which is different.

An earth leakage circuit breaker (漏電遮断器) detects the difference between outgoing and returning current (the leaked current) and cuts the circuit. A thermal relay detects motor overload, a capacitor improves power factor, and a 3-way switch is for switching from two places.

In a 200 V circuit both wires are ungrounded, so a 2P2E breaker with overcurrent elements on both poles is used. With a 2P1E, if the wire without an element faults to earth, that current does not pass the element and is not detected. A 1P1E opens only one wire, and a switch without elements gives no overcurrent protection.

A locking receptacle holds the plug after you insert and turn it. Rain-exposed places use a rainproof type (防雨形), a screw terminal for an earth wire is an earthing-terminal type (接地端子付), and places with flammable gas use an explosion-proof type (防爆形, marked EX).

A receptacle with an earthing pole has a slot that receives the earthing pin of an earthing-type plug. One with only a screw terminal is an earthing-terminal type (接地端子付). Locking when turned is the locking type. Detecting leakage and cutting the circuit is the job of an earth leakage breaker, not this receptacle.

METI's list covers circuit breakers and earth leakage breakers with a rated current of 100 A or less (for motor use, applicable motor rating 12 kW or less). 30 A or less is the range for switches. 200 A or more and 'none' are wrong.