Can I Over-Engineer the Required Wiring for Installing an Electric Hob?


Postby GrumpyMike » Tue Dec 09, 2014 10:39 am

Hi,

My kitchen has been re-designed, and I want to put an electric hob where the electric oven used to be.

The installation instructions for the hob specifies that it needs a 16 amp spur from the fuse box. My plan was to wire the hob directly to the 30 amp cooker outlet instead. (the oven used to be connected to it, so I know it's functional)

I've been told I'll be breaking the law twice over if I do this!
Firstly, I'm told that I have to follow the manufacturers instructions, and if they say 16 amp spur it has to be a 16 amp spur (not 30 amp).
Secondly, I'm told that only an electrician can work on the oven spur, even if it's not an oven being fitted!

This sounds to me like I'm being quoted the letter of the law, but I can't imagine I'm really going to get into trouble for wiring something to a higher standard than specified.

Am I ?

(just to make it clear, the new hob will be the ONLY thing connected to the old cooker outlet)
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Postby ericmark » Tue Dec 09, 2014 6:49 pm

134.1.1 Good workmanship by competent persons or persons under their supervision and proper materials shall be used in the erection of the electrical installation. Electrical equipment shall be installed in accordance with the instructions provided by the manufacturer of the equipment.

So no if's or but's on that one. However BS7671 is not law although it can be used in a court of law. In real terms it's not hard to swap a B32 MCB for a B16 MCB so really no excuse.

As to qualifications non are required. You must be able to do the work without danger to yourself or others but there is no bit of paper which is needed. You will of course have to complete and file the minor works certificate and in Wales pay the LABC it's fees under Part P in England that has been repealed.

As an employer I would want an employee to have C&G2392 or 2391 but would accept a C&G2382 which says he can read the regulations. But if you have read the regulations then you don't NEED a certificate to say you have you know what is required and that is all that matters.

In the main a B32 MCB is all that is required for oven or hob and I would normally not read the manufacturers instructions as in the main they tell you such silly things like IET regulations must be complied with.
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Postby GrumpyMike » Wed Dec 10, 2014 9:11 am

Thanks ericmark.

You're right, swapping a 32 amp circuit breaker for a 16 amp one is pretty trivial, but that isn't actually what I was meaning. I've been told I need to remove the old 30 amp cooker cable, and the 30 amp cooker outlet, and replace with a 16 amp cable and fused outlet. To me this is nonsense, a cable designed for 30 amps should cope with 16 amp quite easily - this is what I was meaning about over-engineering - the electrician I spoke to seemed to taking the rules very literally, if the manual says 16 amp cable, then 30 amp won't do!!!!!
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Postby ericmark » Wed Dec 10, 2014 9:05 pm

Are you sure he was an electrician? Cable does not come as 6A, 16A, 32A, or 40A it comes with a cross sectional area. 1mm², 1.5mm², 2.5mm², 4mm², 6mm² or 10mm² and there are tables to tell you what current it can carry in respect to the installation method.

One looks at the worst installation method over the run of the cable and that becomes the maximum current capacity.

In the main "Reference Method 100# (above a plasterboard ceiling covered by thermal insulation not exceeding 100 mm in thickness)" is the worst but clearly it can vary.

Reference Method 103# (in a stud wall with thermal insulation with cable not touching the inner wall surface) would require a lot thicker cable so for 16A it would require 4mm² cable which with Reference Method C* (Clipped direct) would carry 37A.

As electricians swapping a B32 for a B16 is easy. It's the B16 to B32 which is the problem. If we have the original installation certificate which would state the cable was good for 32A that's easy but without that certificate we need to check the whole route before we could upgrade as without that paperwork we have no idea why it has a B16 MCB.

So some paperwork which states B32 swapped for B16 to comply with manufactures recommendations for oven would be very good in the future when you want a B32 MCB refitted.

But your comments on what the electrician said to me questions if he is really an electrician or a one week wonder retrained under one of the get rich quick retaining schemes?

I am disabled after an industrial accident and have to use tradesmen I would have otherwise never dreamed of using. When my mother had her door bell hard wired it resulted in some words with the installer who was rather surprised to find their client was a member or the IET and had more qualifications than any of their employees.

You could hear the back pacing over the phone as he realised his standard patter would not work.
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