Chinese household electrical distribution boxes
Hi,
I am an electronics engineer from China. Although I am not a licensed electrical engineer, I have some experience with power electronics, which should be enough for me to install a distribution panel in my own home.
The first picture shows a rural distribution box, and the second picture shows the distribution box in our apartment building. In China, we typically accept 50Hz single-phase 230V power supply (below 12kW) via 6-16 square millimeter cables, or 400V three-phase power supply (above 12kW) depending on capacity requirements (although the standard is 220V, in practice it is often a 0.4kV system). Apartments and cities usually use a TN-C-S system, with a main switch after the repeated grounding point. The power supply bureau is responsible for the main switch at the central office, and then we connect the cable to the apartment, followed by another main switch. The configuration after the main switch is very flexible; some people prefer a main switch with an RCBO circuit breaker + a branch 1P air switch + neutral busbar, others prefer a main switch with an air switch + a branch RCBO circuit breaker, and so on. I prefer a main switch with an air switch + a branch RCBO circuit breaker because I have enough space and the branch RCBO circuit breaker helps isolate faults.
For the first picture, this is a rural circuit of the TT system, so there is no ground wire in the picture. The main incoming line is a 16 square copper double-core wire, and the outgoing lines are 10 square and 16 square copper double-core wires. Since it is a rural circuit, I chose the main switch C50 + slave switch C40 + C40, which is a relatively conservative current limit. Because I bought the wrong size—I only bought M20 waterproof Cable gland—the wires couldn't pass through the waterproof caps at all. None of the flanges could be screwed on. I carefully sealed them with silicone rubber, which looked a bit ugly, but it was okay after putting the cover on. At least it works and is durable.
The second picture shows the electrical panel in my apartment building. It has a 10 sq mm incoming line. I use C10 for 1.5 sq mm branches, C16 for 2.5 sq mm branches, and C25 RCBO for 4 sq mm outgoing lines.
In China, over/under voltage protectors (used to prevent neutral faults) and RCDs on sockets and bathroom circuits are mandatory by law, and surge protectors are mandatory at outdoor cable access points. However, we do not specify the frequency response of RCDs, so AC type is often used. Typical household circuits use type C circuit breakers, and motors use type D circuit breakers. Type A/B circuit breakers are difficult to find in China. RCDs are generally 30mA, though 10mA is also available; we can usually only buy voltage-dependent RCDs.
I would like to know what the power distribution regulations are in your area, thank you!
Incidentally, these RCBOs, due to their small size and with a 6kA breaking capacity, only have magnetic and thermal tripping on the live wire, but will disconnect both the live and neutral wires simultaneously. However, I don't think this is a problem. Since thery are RCDs, any neutral wire short-circuited to ground will cause the breaker to trip rather than burn out the neutral wire. Also, the main switch has thermal and magnetic tripping on both wires.