A Brief Discussion on Japanese Electricity

Although this article uses Japan as an example, the fundamental principles should be applicable across various countries! In Japan, there is a qualification exam called the Electrician Technician License, which allows individuals to operate within different voltage ranges depending on their certification. Generally, wiring for household appliances falls under the category of Class II electrical work, while wiring on utility poles belongs to Class I electrical work.

Classification	DC	AC
Low Voltage	Below 750V	Below 600V
High Voltage	750V ~ 7000V	600V ~ 7000V

Power Transmission

The electricity we use today is transmitted from power plants. The principle of electricity generation primarily involves electromagnetic induction; when a magnetic field changes, an electric field is also generated. In reality, power plants utilize energy sources such as fire, nuclear power, and wind to drive engines, which rotate magnets, and coils are placed at different positions to generate electricity.

Wires have some resistance, which increases with distance. To minimize transmission losses, power plants generate electricity at high voltages and only convert it to 100V using transformers when it reaches stores or homes.

Single-Phase Three-Wire System

One important note is that, to enhance generation efficiency, a three-phase generation system is typically used. While it is technically possible to increase the number of phases indefinitely, research has shown that three-phase is the most efficient and economical method. Adding more phases requires additional wiring and increases maintenance costs.

In general, Japanese households typically use a single-phase three-wire system. This setup includes two live wires, allowing for a 200V supply for high-voltage appliances like air conditioners.

Distribution Board

This section is based on my personal experience and articles found online; I welcome corrections from friends living in Japan if there are inaccuracies.

From my experience in my current home, Japanese houses usually place the distribution board in the bathroom. Each household has three lines entering (two live wires and one neutral wire), which connect first to a "main leakage breaker" before being distributed to various outlets.

It mainly serves several functions:

1. It will trip the switch during a short circuit or if multiple high-power appliances (such as a microwave and rice cooker being used simultaneously) cause an overload.
2. It will also trip if the leakage current exceeds a certain threshold.
3. Phase loss protection.

Phase Loss Protection

In a single-phase three-wire system, if the neutral wire accidentally breaks or if a phase loss occurs, the appliances, originally connected in parallel, will all become connected in series as shown in the image below. Since the connection is directly across the two live wires, the total voltage will become 200V, and if the voltage exceeds what the appliances can handle, it may lead to damage or accidents. At this point, the phase loss protection feature kicks in, monitoring whether the voltage at the load exceeds the rated value, and will trip the switch if it does.

Grounding

Previously, we mentioned leakage currents, but the ability to detect leakage current is significantly related to proper grounding.

In Japan, grounding can be classified into four types: A, B, C, and D. Here, I will introduce two common types: B and D.

Type B grounding connects to the secondary side of the transformer and is linked with the neutral wire. The main purpose is to prevent short circuits between the two sides of the transformer. The voltages on either side of the transformer are completely different (high voltage and low voltage); if a short circuit or contact occurs, it could elevate the low voltage side, which, for instance, would be 6600V in Japan, potentially causing failure of household equipment. Type B grounding ensures that if contact occurs between the high and low voltage sides, a closed circuit is created to detect the voltage and cut off the supply.

Type D grounding is used for lower voltage applications, typically involving inserting a copper rod into the ground, ensuring the resistance is below 500 ohms.

This grounding is completely separate from the previously mentioned Type B grounding; although both involve grounding, their applications differ. Therefore, the idea that the neutral wire is equivalent to grounding is not entirely accurate, nor does grounding simply mean connecting to the neutral wire.

Leakage Current

If, for some reason, the metal casing of a device shorts with the live wire, causing the entire device to be in a leakage state, a circuit can form if someone touches it without grounding. (Device casing → Human body → Floor)

However, if the device is grounded, in the case of leakage, the human body's resistance is significantly higher. Therefore, even if current flows, most of it will still route to the ground. Additionally, Japan typically has ELB (Earth Leakage Breaker) protection, so in cases of leakage, the switch should trip before a person even touches the appliance.

Comparison with Taiwan

In Taiwan, there is often discussion about connecting equipment grounding and system grounding (main electrical panel). However, I haven't seen similar discussions in Japan. Here’s my conclusion, though I’m not sure if it’s accurate:

1. When equipment grounding and system grounding are not connected, leakage can reduce the current that could cause electrocution, but if the current is low, the switch won't trip. Similarly, even with grounding, electrocution can still occur, but most of the current is absorbed by the ground.
2. If they are connected, in case of leakage, it results in a direct short circuit, causing the switch to trip immediately.

The reason Japan may not have shared grounding (there may be shared grounding, but I haven't confirmed it) is that almost all household distribution boards have leakage circuit breakers, which will trip immediately in case of leakage, regardless of whether there is shared grounding. In Taiwan, not all houses may have leakage circuit breakers?

Conclusion

Living in Japan for an extended period naturally sparks curiosity about the differences between the two regions. I currently do not fully grasp the operations and practices of both sides, but I hope my observations and references to online articles provide a foundation for discussion among electrical experts.