I live in Hong Kong and they kind of adopted British electrical standards.

I said "kind of" because they only use Class C (Commercial) MCB; Class B cannot be bought locally. I asked around and they all look at me like I have 2 heads.

The effect of this, based on product specification, is that over-current protection is not as sensitive. This also affects the RCBO protection because they are also rated for Commercial uses (less sensitive; takes more current to trip).

How do I figure out if I can install proper B class residential MCB and RCBO so that it is safer?


Type B only affects the magnetic-trip overcurrent portion of the breaker, designed for detecting short circuits. It doesn't affect the RCD part of the RCBO, or the thermal part of the MCB.

Using Type C breakers is fine unless you have such a long run of thin cable that there isn't enough fault current available to trip it at the far end. Hong Kong codes should force using either a smaller breaker or type B breaker in these cases, but usually volt drop will cause people to use a smaller breaker first.

Using a type B makes you more likely to suffer nuisance trips from motors starting, inrush current from switchmode power supplies (turning on a bank of LED lights can be a serious issue for this), and other similar issues.

Unless you have circuits over 50m in length, according to my copy of AS/NZS3000 which is likely similar to your rules, in most cases Type C is fine.

Commercial vs residential doesn't play into it.

I can't comment specifically on Hong Kong code.

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