any sparkies i need help please urgent!!!!!

[skull-eater]

hi guys i need help just bought a new range type cooker. rated at 12000 watts doesnt say amps and i need to convert it tryed on google its coming out at 50amps which sounds alot to me.this what weve got in our electric box:
cooker 32a
sockets 32a
garage 32a (theres only a light and chest freezer in there)
alarm 16a
lights 6a
conservatory 32a(theres only a light and fan and telly dvd player)
and its a 80a box please help wifes nagging at me

[Jenn]

If you're not sure what you're doing I'd advise getting an electrician in instead. It might cost you £50 or something but then you know it's safe.

Also there is the Part P regulations that look like they apply to cookers.
http://www.partp.co.uk/consumer/consumer_diy.asp

[Steve.EX]

Hi.
I am in the 'trade' (although an engineer) and 12kw does indeed equate to approximately 50amps.
Simply divide 12,000(w) by 230(v) and theres your current (a).

There is a practice known as diversity within the domestic (and to some extent commercial/industry)
This is a basis on which total 'probable' load is calculated. In the domestic enviroment although the main switch on your consumer unit will be rated at 80 or more typically 100a you will have many outgoing circuits that in total may exceed that rating.
But for instance domestic ring-mains (rated at 32a each) you do not allow the sum total. Without my books to hand (i am more supplies to industrial premises based) i believe the first ring main is rated at 100% and then remainers at either 50 or 30%. The same scales of diversity are allowed for lighting. The only circuits to which no diversity can be allowed are direct-loads, i.e those of a heating nature - immersions, showers, etc where they are either on or off, when on full load is always applied.
Whilst 50 amps is quite a load for a domestic cooker it is unlikely that you would have all rings and elements on at a single time. What is important is that the supply cable and isolators to the cooker are of a correct size. These are normally wired in 6.0mm PVC T+E and are usually comfortable with loads up to 40 amps. 50 amp loads require a minimum of 10.0mm cable and maybe larger dependant on what building materials theu are installed in/through.

HTH.

Steven

[Steve.EX]

As stated above there are also issues of Part P. This will generally revolve around the necessity of bringing all circuits, pipework and extraneous metal conductive parts to a common earth-path. This however (imo) should be a secondary consideration against ensuring the supply cable to the cooker is 'man-enough' to carry the load. I would not connect anything to anything without establishing:
A) There is earth-continuity within the supply circuit (earth-loop impedance)
B) The cables and MCB are correctly rated.

[njp]

Originally Posted by Steve.EX

Whilst 50 amps is quite a load for a domestic cooker it is unlikely that you would have all rings and elements on at a single time. What is important is that the supply cable and isolators to the cooker are of a correct size. These are normally wired in 6.0mm PVC T+E and are usually comfortable with loads up to 40 amps. 50 amp loads require a minimum of 10.0mm cable and maybe larger dependant on what building materials theu are installed in/through.

Is it even possible to fit an MCB rated at 50A to a domestic consumer unit? I thought the limit was 40A or possibly 45A...

[Steve.EX]

No, i believe most of the majors (Hagar, Contactum, Crabtree and MK etc) offer 50a MCBs for their domestic consumer units. They are all no doubt of a type B (operating curve) only, this however will be fine for the purpose which you require.
Is there not two connection units on this type of cooker appliance, i.e one for the main ovens and one for the hob unit?
You could then split the load between two circuits if necessary.

[Steve.EX]

http://www.mkelectric.co.uk/products...1&rangeid=1051

An example?

[njp]

I stand corrected. But as the OP says he has an 80A CU, I suspect fitting one of these wouldn't be an option, even if he uprated the cable.

[sore napper]

Originally Posted by Steve.EX

These are normally wired in 6.0mm PVC T+E and are usually comfortable with loads up to 40 amps. 50 amp loads require a minimum of 10.0mm cable and maybe larger dependant on what building materials theu are installed in/through.

Indeed. If your old cooker is wired in 6mm you need to rewire it with 10mm.

Add a new 1 way consumer unit with a 50A MCB. Feed the new box with mains from the eskos.

You will also need to change your cooker switch in the kitchen as its only rated at 45A.

I think you should get someone in to do it. If they have to cut walls and stuff I say it would cost £200-£300

[Steve.EX]

Originally Posted by njp

I stand corrected. But as the OP says he has an 80A CU, I suspect fitting one of these wouldn't be an option, even if he uprated the cable.

This will only indicate the current carrying capacity of the main switch contacts. unless his unit is an old wylex unit (their 6 and 8 way boards were rated with an 80a main switch) then i would assume that the actual busbar is a standard 100a.
Todays manufacturers will only make 1 busbar per range (rated at a minmum
of 100a) regardless of which main switch-disconnector you actually install on it.

[plasmad00d]

Maximum demand for cooker ....

First 10A of rated current + 30% of the remainder + 5A for socket outlet (if fitted)

Also if socket outlet is fitted to cooker switch and it can be reasonably expected to supply portable equipment for outdoors , it must be protected by an RCD not greater than 30mA.

Unfortunately having a cooker circuit protedted by an RCD could cause "nuisance tripping" when the elements are switched on from "cold". Best practise is to do without a socket outlet on the cooker switch and therefore negate the use of RCD protection on cooker circuit (providing the other sockets in the house are protected)

[njp]

Originally Posted by plasmad00d

Maximum demand for cooker ....

First 10A of rated current + 30% of the remainder + 5A for socket outlet (if fitted)

Where does that come from then? In my experience, the most common use for a socket associated with a cooker circuit is to power a kettle, which can easily be rated at 3kW...

If we assume no socket (as is usually the case these days), that calculation places the maximum demand for his (presumably rather large) cooker at 22A, which is comfortably lower than the normal 32A circuit. But it seems a rather optimistic figure to me. Surely people only buy large cookers if there is a reasonable expectation that they will be using most (or all) of the heating elements at once, even if only occassionally? I don't see how that diversity calculation makes any sense...

[plasmad00d]

Originally Posted by njp

Where does that come from then?

Its from B.S. 7671 , in a domestic situation. Its called maximum demand and diversity.

[Steve.EX]

I tend to think that he is quoting directly from B.S7671 or Guidances Notes etc.
You will find that it is correct.
Unfortunately the industry has much changed over the last 15 years. In time past there were specific guidance (I.E.E B.S7671 15th Edition and earlier) that were quite specific about what you could and could not do (i am now refering to a domestic commoner-gardener electrician). This was good for the 'sparkies' in so much as regulations were very clear-cut. Over the years however their have been countless incidents involving legal/criminal actions from minor to very serious incidents. In days gone by it provided the tradesman with some protection in that they were able to wave their I.E.E Regs books and say; "we followed these exactly".
Now today the Regs book consists of some several hundred pages, much of it written in unfriendly 'lawyer' type speak that actually offers very little by way of exact guidance. Both the I.E.E and to a lesser extent the N.I.C and E.I.C have now adopted a; you can do what you want as long as when it goes tits up you can 'prove/validate' your choice of installation, wiring and accessory methods. It has become a minefield of responsibility for the man on the ground.
Strangely the I.E.E Regs are not, and never have been a statutory document. They hold no legal basis and are when all is said and done guidance notes only. This has presented my domestic kin with something of a paradox as i understand it as when Part P came into being (Jan '05) it basically meant that (i.e) Kitchen and Bathroom areas fall under Building Regs, which is a statutory legislation and law enforcable. So what you have is an enforcable area in terms of installation (there is however quite clear guidance on zoning and I.P ratings etc) but still the open-endedness of install it how you like and with what cable you like.
A classic example being a whole section of the Regs is dedicated to cables and their current-carrying capacity, along with volt-drop per meter and co-efficents for building materials that they maybe sat on or in etc. However this can all be disregarded if the cable manufacturer (and in my experience when you phone up these people i am hardly ever convinced the man on the phone entirely understands the importance of accuracy) says otherwise.
This all then has to be documented as a form of proof should any 'issues' arise.
It has been many years now since i was involved in the trade at this sort of level and there is no way i would go back to it.
Fortunately the 'rules' governing HV supplies are somewhat more long-standing and robust (although still have the odd area for personal interpretation!)
And to think compared to other E.U countries we are actually 'very-safe'.

A little history thingy for you.

[plasmad00d]

Originally Posted by Steve.EX

Strangely the I.E.E Regs are not, and never have been a statutory document. They hold no legal basis and are when all is said and done guidance notes only .

Yes it is quite a minefield and although B.S.7671 are not a statutory document , they are a minimum requirement in a court of law (if it should go that far).