Life Hacks in Japan

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"Life in Japan" Even if a 3P (pole/pin) plug is converted to 2P (pole/pin) with a conversion adapter, grounding is still required!

(Updated June 12, 2022)

"The plug is 3-pin and I can't plug it into an outlet. Yes, let's use a conversion adapter!" Are you taking the easy way out like the aforementioned? 3P or appliances with cables like this have a high risk of leakage current and need to be grounded. This is an important issue, so let's examine it carefully!


What is leakage current?

The Kansai Electrical Safety Association explains leakage as follows

Normally, electrical wiring and appliances are "insulated" to prevent electrical leakage.
Electricity leakage occurs when cables are damaged or aged and their sheathing is peeled off, causing electricity to flow outside. Leakage can also occur when water is splashed on non-waterproof electrical appliances, resulting in poor insulation.
This electrical leakage is a very dangerous phenomenon that can lead to electric shock and fire.
[Basics] About Leakage Electricity | Electricity in Your Life | Useful Information on Electricity | Kanto Electrical Safety Association


This video shows an actual experiment with an electric leakage. As explained in the video, even if a leakage of electricity occurs, grounding allows the leaked electricity to escape to the ground.


Risk of electric shock

For example, in the case of a hair dryer, the following amount of current flows

When using a hair dryer with a power consumption of 1,000W, the current flow is 1,000(W) ÷ 100(V) = 10(A) because the voltage in Japan is usually 100V.
Volts, Amps and Watts - Knowledge of Electricity


The number 10 seems like a small number. However, as shown in the table below, assuming that the body receives all the current, even a current of 1 / 100, or 100 mA, will cause death. Even if you do not die, there is a good chance that your body will be damaged.

Electric Shock | Kyushu Electric Safety Association


What needs to be grounding

The inspection standards established based on the "Ministerial Ordinance Establishing Technical Standards for Electrical Equipment" are the "Internal Line Regulations. The necessity of grounding is determined in three levels of "obligation, recommendation, and recommendation" in the extension regulations.

Obligation (must be adopted)

・An outlet with a grounding pole shall be installed for the power supply of the specified equipment. (Article 3202-3.1)


・Outlets for 200 V to be installed in residences shall use outlets with grounding poles. (Article 3202-3.2)

Recommendation (mandatory operation is basic Application is also allowed)

・Outlets installed in kitchens, kitchens, washrooms, lavatories, etc. shall use outlets with grounding poles. (Article 3202-3, Section 4)
[Note] Outlets with a grounding pole should be equipped with a grounding terminal.


・Outlets installed outside the rooftop rain line or outdoors shall use outlets with grounding poles. (Article 3202-3, Section 4)
[Note] Outlets with a grounding pole should be equipped with a grounding terminal.

・Outlets for 200 V installed outside of residences shall use outlets with grounding poles.

All electrical outlets installed in residences other than specified equipment and specified locations shall use outlets with grounding poles.
Extension Regulations Toshiba Lighting & Technology Corporation


RCD (Safety Circuit Breaker) Comparison Table

A device that detects leakage current and interrupts the current is called a leakage current circuit breaker. Monotaro, a major industrial products e-commerce site, explains it as follows. In a nutshell, it is a mechanism that stops when electricity escapes from the ground wire due to leakage.

RCDs are designed to detect the difference in absolute value between the going and returning currents in a circuit and interrupt the circuit if the difference exceeds a certain level.


In the case of a leakage, the current escapes to ground, resulting in a difference in current value. As a result, a voltage is applied to the coil that detects leakage current. This is amplified by the control circuit, and if the difference exceeds a certain value, the circuit is shut down.
Principle and Usage of RCDs [Mail order Monotaro] (Japanese only)


If left unattended, they can cause fires, so it is safer to have a RCD. The following two companies are well-known manufacturers, but their functions seem to be the same.

Manufacturer Toshiba Lighting & Technology Corporation tenpearl
model number LBY-120C GR-XB1515
Rated voltage AC100V AC100V
Rated current 15A 15A
Rated sensitivity current 15mA 15mA
Rated nonoperating current 7.5mA 7.5mA
Operating Time Within 0.1 second Within 0.1 second


Why RCDs alone are not enough

If you want to connect to a leakage breaker that requires a 2P + ground wire to be attached, as in the two types above, you will need an adapter to convert it to a 2P + ground wire if the appliance you use has a 3P plug.

Many people think that if they install a ground-fault breaker, they will be safe. However, it is meaningless if the ground wire is not also connected, as it will shut off the ground wire if electricity comes to the ground wire due to a leakage.

The following types of conversion adapters are available

Manufacturer Name Sanwa Supply
Product name TAP-AD9W TAP-AD8 TAP-AD1
variety white Black/Gray Black/Gray
Use in 3P × ×
Use in 2P
Insulation Covers
thermal fuse × ×
thermosetting resin × ×
Price* 1,499 yen 273 yen 230 yen

*Prices on Amazon as of June 12, 2022.


Thermally fused (shuts off at high heat)


Thermosetting resin (heat-resistant *No fuse, so electricity will not stop even at high heat)


Normal type (cheapest)


Two together cost about 3,000 yen. For safety, be sure to ground what is required by regulations.

I hope the above is helpful. Please also see here!