Main breaker has two different sized cables going into it

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UsernameNotAllowed

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#272795 16-Jul-2020 13:10

Our switchboard has a two pole main circuit breaker with one larger and one smaller cable coming into it. I'm wondering what this smaller cable is for. Both cables are 235V as I measured. Is this smaller cable like a 'supplementary' cable as the larger one is not enough?

I have attached a picture below:

Any ideas on this smaller cable's purpose? Thanks

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Tracer

343 posts

Ultimate Geek
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#2524973 17-Jul-2020 20:27

That's your hot water supply. It's controlled by a ripple relay so the network can switch it off at peak times and goes through a separate meter (usually combined into one unit on modern meters) so it can be billed at a different rate. As the ripple relay and meter are in the meter board you need a separate wire coming into the switchboard, and since you still want the main switch to turn everything off, you have the two separate poles on the main switch. The cable is smaller because it's only 16 or 20 A for the hot water only, whereas the main is likely sized for 63 A to feed everything else in your house.

larknz

1983 posts

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#3353264 12-Mar-2025 17:49

The symbol shows a switch, not a circuit breaker and there is no Type number.