Going back to the oven, it's not 100% clear to me whether the hob is still running from the same circuit. If not, it might well work on a B20 or certainly a B25, in which case the oven-maker's requirements might be met if one can find out what they are?
Yes, the hob is still upstream on the same circuit so as you say I don't want to reduce the OCPD.
Thanks for the other info - I was never serious about the fuses thing - but good to know some more theory.
Even a 3A fuse won't protect a fan motor from catching fire, so there is no relationship between the external OCPD for the oven and its current-using components. The manufacturer really ought to state what protection is required, which is quite likely determined by the need to protect the internal wiring against short-circuit.
The instructions are a mixture of a couple of helpful sentences on the website and a downloaded manual that appears to contain a copy/paste set of rules.
The website says:
"No plug is included. Installation to be carried out by a qualified installer."
"Minimum fuse = 16 amps"
Fine so far. The complete downloaded guide says:
-Make sure not to cause damage to the mains plug and to the mains cable
• The appliance must be earthed.
• Make sure that the parameters on the rating plate are compatible with the electrical ratings of the mains power supply.
• Always use a correctly installed shockproof socket.
-Connect the mains plug to the mains socket only at the end of the installation. Make sure that there is access to the mains plug after the installation.
• If the mains socket is loose, do not connect the mains plug.
• Do not pull the mains cable to disconnect the appliance. Always pull the mains plug.
• Use only correct isolation devices: line protecting cut-outs, fuses (screw type fuses removed from the holder), earth leakage trips and contactors.
• The electrical installation must have an isolation device which lets you disconnect the appliance from the mains at all poles. The isolation device must have a contact opening width of minimum 3 mm.
It looks like to fully follow the letter of the instructions a 16A socket would have to be fitted. I also believe a lot of these points are copied and pasted from other products. But no mention of a required
maximum fuse or overcurrent device.
The circuit is RCD protected (the house happens to be TT). I know that thousands of these must be fitted without this degree of thought but my main concern is (still) a L-N short circuit as I don't trust the internal wiring to withstand the fault current allowed by a 32A breaker.
Ultimately the choice seems to be
a) dual plate, at least 2.5 sq mm T+E for single socket for microwave (433.2.2 allows this as
@APE37 mentioned), connect oven in as no manufacturer maximum fuse is specified
b) Stick BG garage board in cupboard and run a 20A circuit for the oven and 16A for the microwave.