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I want to replace my old hard-wired oven. The old oven requires 1.6 kW whereas the one I want to install requires 3.6 kW. Like the old one, the new one is also intended to be hard-wired. There is an isolator switch in the kitchen for the existing oven, wired back to the circuit breaker in the consumer unit. The corresponding circuit breaker is rated at 32 A; much more current than is actually required (I'm in the UK so mains voltage is 230 VAC). I'm wondering, however, whether it's safe to assume the internal house wiring between the circuit breaker and the isolator switch in the kitchen will also be rated to carry 32 A and thus safe for the extra 2 kW of power draw. I can't easily inspect the house wiring otherwise I'd just measure it.

I suspect there will be legislation that requires wiring to be rated to meet the corresponding circuit breaker's rating, but I'm not an electrician and don't know if it's safe to assume this is always the case. My house was built (and likely last wired) in the early 80s in case that's relevant.

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    In North America the circuit breakers protect the wires, so the wires must meet the breakers size requirements and cannot be smaller. I imagine it is the same in the UK. Unfortunately it is possible someone in the pass as put in a larger breaker, because the one that was the right size was tripping, so a bigger breaker stops the tripping, but causes a fire hazard. In NA a 32 amp circuit should have 8 gauge wire(google for local conversion). The isolator switch might have a smaller fuse in it. I think that is how UK circuits work, a powerful ring circuit with fuses at the outlets limit amps
    – crip659
    Apr 1, 2023 at 22:44
  • @crip659 I think you're right that the circuit breakers protect the wiring in UK circuits too. I did consider that someone may have installed a higher rated breaker to fix a tripping issue, but since the circuit is the only one labelled "Cooker" in my consumer unit and that 32 A is a common rating for cookers, I'm inclined to believe my house's wiring will be completely fine for my new oven. I've linked to an informative video in my answer below. Thanks for your input - and for the pointer to check the isolator for a fuse - good idea!
    – Sean
    Apr 1, 2023 at 23:24

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According to this video on UK cooker circuits from electrician John Ward, UK house wiring for cooker circuits almost always uses a 32 A breaker at the consumer unit and the wiring is usually 6 mm² which is more than sufficient for the current. As he explains, in almost all cases 4 mm² wiring would be sufficient even for 8+ kW combined electric hob/oven units but houses typically use 6 mm² for legacy reasons (which fortunately gives even greater margin over the 32 A breaker rating). Throughout the entire video he calculates the wiring for various kitchen appliance combinations in the context of the 32 A breaker, which gives me confidence that indeed the wiring choice is defined by the breaker rating, and so it seems likely to me, under the assumption the wiring was correctly installed, that my new oven will not overload the circuit's wiring.

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  • AFIK in the UK low power appliances which are plugged into high current circuits have a fuse in the plug. Do hard wired loads have a fuse in them to protect the wiring connecting the load? Apr 2, 2023 at 2:24
  • @JimStewart that's a good question that I don't know the answer to! Note that "hard wired" really means the cable from the oven is screwed into a terminal in the kitchen that is itself wired to the isolator switch (typically at counter top level) that is then wired back to the breaker. I assume there will be a fuse in either the screw terminal box or the isolator, but I've not opened mine up to check yet. I'll report back here if/when I do.
    – Sean
    Apr 2, 2023 at 8:42
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    In the US "hard wired" would not have a place for a fuse compartment in line. If there is no fuse in your situation, it almost certainly is not necessary. For a fuse to be practical it would have to be accessible without pulling out the appliance. Apr 2, 2023 at 12:28

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