For those following, it is likely that I will elect to add a 45A breaker for my cooker circuit to satisfy the building control inspector chappie. My CU is Hager who don't do 45A breakers therefore I may be looking at a separate sub-box.
The questions are:
Should the tails for this connect downstream of the existing CU switch, so that the CU switch controls the whole install? Or should they be upstream of the CU switch - requiring isolation of the main fuse to fit?
Also, what enclosure/device do the group recommend?
I recommend you do the work to BS7671, then let him a) refuse the certificate and you require him to state why in writing quoting relevant chapter of BS7671 b) do an S38 enforcement notice or c) brings in council idiots who do unsolicited and unnecessary work which the competent scheme member will have to both reverse and you do not have to pay - by law.
MK do 45A circuit breakers, but this is irrelevant because you do not need to do what you are being requested.
Additionally you may find the cooker manufacturer stipulates a maximum breaker size, I know Creda & Hotpoint used to. For example my 1996 cooker specifies 32A breaker required. Likewise you could contact the appliance manufacturer and see if they have a recommended size.
Remember a) P1 requirement of Part P and b) nothing shall be required beyond compliance with BS7671. Full stop. They can not create "urban myth" regulations otherwise we are into "punitive punishment because you took a job away from one of our scheme members nonsense".
Tell your BCO you are going to fit a gas cooker! Get him to sign it of as complete (cooker does not need to be there - its an appliance). Do it right once he has gone!
Normally if using multiple CUs then I install a main switch in a separate enclosure prior to them. Having said that, there is no absolute requirement to.
But there is a requirement for every electrical installation to have a single main switch. If you split the meter tails without providing a single point of isolation then you actually have two or more separate installations, according to NICEIC's FAQ.
Q13. If a dwelling has an existing consumer unit with an integral main switch, and an electric shower is connected by means of a second consumer unit with an integral main switch, is another =91main switch=92 required to isolate both consumer units simultaneously?
Regulation 537.1.4 requires a main linked switch or linked circuit- breaker to be provided as near as practicable to the origin of every installation as a means of switching the supply on load and as a means of isolation. However, it is permitted for a dwelling to have more than one electrical installation. Therefore a further =91main switch=92 is not required to isolate both consumer units. Regulation 537.2.2.6 requires each device used for isolation to be clearly identified by position or durable marking to indicate the installation it isolates. Regulation number(s) 537.1.4
... neither do ESC of course.
Adding a 3P+N isolator can be expensive, particularly if there is no space, and is thus an expensive lead-in - or engineered means to recover fees for Our Members. The critical point is that it must be labelled - eg, E7-Timed-CU & 24/7-CU or House-CU-ex-Shower & Shower-CU.
Indeed - of those I have seen, ones without a main switch are very much in the majority... (in fact the only ones I can think of with a main switch were the ones I installed!)
Which is actually saying the same thing. If you add another CU without a main switch upstream, then the premises now has two installations rather than one.
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