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I plan to run electricity to my detached garage workshop. The electrician I found had a look at the wiring in the garage and said I have to use ring circuit otherwise the fuse will trip.

My current wiring in the garage is the a 2.5 mm T&E cable going through a junction box which splits into two radial circuit of sockets (2 and 5 sockets respectively). The maximum load I calculated is around 3.5 KW. The electrician intends to use a 16 A MCB for the sockets. What I don't understand is why making it into a ring circuit will not trip the breaker but my current setup will, providing the load is the same and below the MCB.

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  • This is in the UK, right?
    – ThreePhaseEel
    Commented Jan 9, 2021 at 19:41
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    Yes. It's in UK
    – moho wu
    Commented Jan 9, 2021 at 19:41
  • WOW, Never heard of a "ring circuit" before. I learn something here almost every day.
    – George Anderson
    Commented Jan 10, 2021 at 0:03
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    @george Anderson, you have prrobably never heard of a ring circuit, because although common in the uk, the way they arre done would be too many code violations to count in the usa, possibly anywhere else. The idea was to save a miniscule amount of copper so you can use wire rated for 16a for a 32a circuit as there are 2 paths to any given point. Of course, if the wire breaks anywhere, all outlets work but you have a dangerous situation. Be glad you never heard of them in my opinion
    – camelccc
    Commented Jan 10, 2021 at 12:13
  • if you dont want a ring, install 2 circuits like every country other than the uk does
    – camelccc
    Commented Jan 10, 2021 at 12:17

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I think I have an answer to my question now based on some research. So if a 16A breaker is installed and the maximum load I have is around 3.5 KW, it won't trip whether it's ring circuit or radial circuit. However I decided to put it into a ring circuit in the end because of the way I wired my workshop. The wires are surrounded by insulation and going through wall studs. As a result it's not the best setup for heat dissipation. Based on this table my wiring method reduces the current capacity of 2.5 mm cable to only 13.5A using radial circuit, which is not enough for my need. It won't trip the breaker but it'll be a fire hazard. If I make it a ring circuit I'm effectively doubling the cross section of the wires making it 5 mm cable. With my installation method, it can sustain around 20A, which suffices my need.

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