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I have a couple of contractors renovating my kitchen and I have two appliances that I will need them to install:

  • an induction cooktop (7600W max power, three-phase)
  • a built-in oven (3600W max power, single-phase)

In the kitchen, where we want these devices to be installed, we have a single three-phase cable available. Our contractor said that he can hook up both devices off that cable. While I know that it's possible, I'm wondering if this is normal practice and whether I should hire someone to install a separate cable for the oven?

If they do install it as they suggested, do I need any changes to my electrical box? (see the photo below, I translated relevant parts)

Electrical box

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    Where are you on this planet? Commented Aug 27, 2021 at 11:26

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Sure, in Euro-countries you can take that 3-phase wiring ("Wye" configuration, with neutral) and simply treat it as three single-phase circuits of that ampacity, sharing a neutral.

Or a 2-phase circuit and a 1-phase circuit.

So you can put the oven on 1 phase, however that will use the entire capacity of that phase.

The cooktop seems slightly too large to fit on 2 phases. However, I suspect European codes give an allowance for the fact that not all "burners" will be 100% all the time (they cycle on/off naturally). So it may be alright, if the cooktop provides a wiring diagram for 2-phase connection.

Typically cooktops have a connecting block allowing them to be jumpered either for "all on 1 phase" or to distribute the "burners" across different phases, to avoid overloading any one of them.

My concern is one phase is at maximum due to the oven. If the cooktop's "burners" are spread across all three phases, then the oven + the burner(s) on that same phase could overload the circuit and trip the breaker.

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    To put some numbers to it, 3600W single phase is about 15A, very close to the 16A of the breaker. 7600W spread across two phases would be 16A per phase. But spread across 3 phases would be 11A. Obviously, 11A + 15A is rather more than 16A.
    – Simon B
    Commented Aug 27, 2021 at 21:16
  • The manual provided with the oven recommends a 16A breaker. The cooktop provides a schematic for a two-phase connection but doesn't go into detail on what breaker to use (at least I was unable to find any details on this). If we do go this route, I'm wondering if the 16A breaker will be enough to operate without it occasionally tripping (i.e. (7600/2)/230 = is roughly 16.5A).
    – martynas
    Commented Aug 30, 2021 at 6:19
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    @martynas The C16 will likely never trip: An "C"-type breaker allows for an longterm (thermal) overload factor of 1.13–1.45, for over an hour. The instant (magnetic) overload factor is 5 to 10. Frame challenge: Some induction cooktops have the option to program a limit on power consumption
    – Martin
    Commented Sep 1, 2021 at 22:18

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