Comsumer Unit and New hob and Oven Question

I think you mean the plugin MCBs not RCDs (your installation is a already protected by an RCD) Like this

They have their pros and cons but your money would be better spent getting the board upgraded.

To answer your second question the load characteristics of the appliances would be helpful.

 

Looking at the pics again - it may be time to get a spark round to at least inspect the current installation as this looks suspiciously like your main earth terminal

 

Looks like a TT set up as well. Does look an old installation and I'd want a quick check of the electrics before stuff is altered myself.

On the oven front, if it comes with a plug then I would wire a single socket off the cooker circuit, after the isolator switch. and plug it into that.

 

Also how is the 6mm cable installed? for example conduit in wall, clipped direct, above a plaster board ceiling covered by insulation exceeding 100mm, above a plasterboard ceiling covered by insulation not exceeding 100mm. What's the KW rating of both appliances?

 

cant you google the make/model?

 

With Cf factored in, the current carrying capacity of the 6mm is about 27A. Diversity can be applied to the oven and hob.

 

27A for a 6mm? I'd want that from a 2.5 I suspect this is from the expensive yellow book again, its just £80 of mumbo jumbo.

 

well obviously its from the BYB and previous editions. Any circuit protected by a BS3036 fuse should have the correction factor of 0.725 applied to the tabulated CCC of the cable.

 

So what do you do, go and hunt down a 15A re-wireable fuse so it covers it because its still on a re-wireable? If you are changing the fuse/carrier why not put a 32A plug in MCB in instead? Its got a fixed load on it anyway so whatever fuse/mcb you protect it with the current on the cable ain't changing.

You could protect that cable with a 40A MCB and I can 1000000000% guarantee that nothing will ever go wrong with it. It may be against the regs, it may not be, I just feel there are more important things in life to worry about than a book of words.

Everything you think you are doing safe now will be deemed dangerous practice in a couple of years from now when they have another book to sell, I wouldn't pay too much attention to it really.

 

yes it may well have a fixed load but the cable still has to safely carry that current. The correction factor for semi enclosed fuses is due to thermal constraints on the cable under overload and fault conditions. When omitting overload protection the CPC CSA needs to be of an appropriate size based on the chracteristics of the OCPD and PFC.

Of course there are more important things in life than a book of words as you put it but as I chose a career as an electrician i feel its necessary to have a better than average understanding of the regulations of which we operate.

 

Oh I understand the regs I just dont devote my life to blindly following each and every one of them, some I find quite idiotic.

Take the volt drop one, apart from the fact most things will work quite happily on a large range of voltages anyway the regs say that volt drop is the holy grail and must never drop below 3% otherwise armageddon will ensue and then a couple of pages later say oh by the way we cant guarantee voltages at peak times so you will have to factor in the Cmin.

What a load of old ****.

 

volt drop is mentioned in Appendix 4 which is only informative. volt drop should not exceed the limits stated in the relevant standards of the equipment to be installed. If the limits are not stated then it should be of a limit that does not impair the safe functioning of the equipment.The requirements of volt drop are deemed to be met where they don't exceed the values stated in appendix 4.

 

I would change the wired fuse personally, Plug in MCBs cost less than a tenner, you will have to change the guard at the back of the fuse as well though , easy enough but turn the main switch off first.

If the oven comes with a plug on then wire a single socket off the cooker cable. If it doesn't I would be happy for the 6mm and hob feed to sit on a 32A MCB or even possibly a 40A but maybe not the thinner flex of the oven, it all depends on what the oven says it should be connected to.

 

I think a qualified sparks to do the job is indicated Steve