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Understanding Voltage in Japanese Homes

In the previous article, I talked about DIY infrastructure projects for electricity, gas, and water. In this article, I’ll go into more detail about electricity in Japanese homes.

If you’ve ever been to Japan, you may know that homes typically use a 100-volt power supply. However, did you know that 200-volt power is also used in some homes?

Single-phase 200-volt power is often used for appliances that consume a lot of electricity, such as IH (induction heating) cooktops, electric water heaters, and powerful air conditioners for large rooms. Since using 200-volt power requires special outlets, wiring, and circuit breakers, it’s a good idea to plan ahead and decide where these high-power appliances will be installed if you’re renovating.

Modern distribution boards (circuit breaker panels) often include branch breakers that can switch between 100 and 200 volts. However, older panels may not support 200 volts. If this is the case, you’ll need to either add a 200-volt breaker or replace the entire panel. Keep in mind that the lifespan of a distribution board is generally 10 to 15 years. Experts recommend replacing it after about 13 years, so if you’re renovating an older home, updating the panel is a smart move.

Many of the distribution boards sold these days have a number of 100-volt and 200-volt switchers, such as the six branch breakers on the far right of the photo.

Older distribution boards do not have switchable branch breakers, so if there is no 200-volt branch breaker, the 100-volt one must be replaced with a 200-volt one or a 200-volt branch breaker must be added.

In Japan, the standard for home electrical wiring is 1.6mm VVF (Vinyl insulated Vinyl sheathed Flat-type) cables. However, for 200-volt applications, thicker cables, like 2mm or 2.6mm VVF, are often used. While it’s technically possible to use 1.6mm cables for 200-volt devices with low power consumption, it’s safer to use 2mm or thicker cables. Thinner wires carrying more electricity than they’re designed for can overheat and pose a fire risk.

The outlets for 100-volt and 200-volt power are designed differently to prevent mistakes. There are also two types of 200-volt power in Japan:

1. Single-phase 200 volts, used in homes.
2. Three-phase 200 volts, used in factories and other industrial settings.

The outlet shapes for these two types of 200 volts are also different. This is because their power transmission systems are not the same, even though both are 200 volts.

If you’re renovating or using a property like a factory, warehouse, or restaurant that previously supported heavy electrical equipment, you might find three-phase 200-volt outlets or panels. Be cautious―these outlets can only be used with equipment specifically designed for three-phase 200 volts.

From left to right in the photo: 15 amp 100 volt outlet, grounded 15 amp 100 volt outlet, 20 amp 100 volt outlet, and grounded 15 amp 200 volt outlet. There are several other types of outlets besides the one in this photo, as the shape of the outlet varies slightly depending on the amperage as well as the number of volts.

Many countries, unlike Japan, use 220-240 volts as the standard household voltage. If you’re from such a country, you might wonder:
"Can I install outlets from my country in my Japanese home and use my imported appliances here?"

The short answer is no―it’s not practical or legal. Electrical components used in Japan must comply with the PSE (Product Safety Electrical Appliance & Materials) law, and most foreign components don’t carry the required PSE mark. Without this certification, a licensed electrician in Japan is unlikely to install them for you. Installing uncertified components yourself is also illegal and risky.

However, if you use PSE-certified Japanese outlets, you can install a 200-volt outlet and use your appliances with a suitable conversion adapter. Be aware, though, that appliances designed for 220-240 volts may not work optimally on Japan’s 200-volt power supply due to the slightly lower voltage.