Dave Plowman (News) wrote:


Our problem is how to connect a new multi function oven. The spec is
3.6kw total connected load. Elsewhere it says it is fitted with a plug
(which it isn't) and must be installed via an earthed socket with fuse
protection of 16a, unless the plug is not accessible then an all pole
isolator must be used on the connection side. it later says in the GB
to permanently connect it and use the isolator.

Remove the existing FCU and replace it with a cooker connection unit. This
is essentially a 45 amp connector block mounted on the back of a one gang
plate with a cable outlet. Run 6mm cable from there to the oven.
This type of oven doesn't normally have any internal or external fusing
other than the main MCB.

Yup. Doing this means violating the letter of the installation
instructions; but it's hard to conceive of this actually affecting
safety materially. The fusing in the supply is to protect the cable, not
the appliance: by running the cable as 6mm all the way, you're using
cable which can take the nominal rating of the 32A MCB indefinitely.
(Since the oven won't generate a load of more than 3.6kw = 15A@240V, you
could wire its drop from the FCU in 4mmsq or even 2.5mmsq, but that
would require calculations to show it's safe (they've been done here on
this NG, and been so shown for 'reasonable' lengths of feed and tail;
but sticking to 6mmsq keeps any 'ordinary' and/or picky NICEIC
periodic-inspecting type in familiar territory...). It's *extremely*
difficult to construct a plausible scenario where some appliance fault
would be cleared by a 16A breaker but not a 32A one - the fault
resistance would have to be unusually high and in a very precise band of
values for that to happen.

Stefek