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PostPosted: Fri Apr 06, 2018 9:29 pm 
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Hey all.. I am having an induction hob installed instead of my current gas hob.. Currently I have my cooker power switch approx 4m from my fuse box (6mm cabling to a 32Amp breaker) . This then has 6mm cabling to a single power socket that my oven is plugged into.. I had presumed that when i get a sparky round he would change the single power socket to a cooker switch with socket and wire the hob in...

BUT he is adamant I need a whole new 6mm cable to the new hob... The hob is 7.4KW and the oven is rated at 2.1 KW...

The question is... is he trying to get one over on me and charge me for work that really isnt needed, or he is correct in his statement.. Reading various places it appears most people say its fine to run them both on the same 6mm because of diversity (although i gather diversity is about not all the hob rings and oven being in use at the same time... but what happens that one time on xmas when they are?

If it matters the house is 18 years old, and the wiring hasnt been touched since the house was built.

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PostPosted: Fri Apr 06, 2018 10:50 pm 
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7.4 is 32amp on its own[7400 div by 230=32.2a]
diversity will allow a bit off leeway but how much need to be worked out :dunno:
suspect 2.1will be ok but a close call :dunno:
although i think diversity tends to be over the whole house load rather than point loading on a single circuit

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PostPosted: Fri Apr 06, 2018 11:17 pm 
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If the supply is from a 32A MCB with 6 mm cable worse case scenario is it trips, and no real harm is done, worse case is Christmas Turkey oven been on 3 hours and power trips meaning no cooling fan, but that is highly unlikely.

So an induction hob uses less energy than any other hob to cook the same food, so if 32A was enough 40 years ago for the old 4 ring and oven cooker, since now more efficient it will not be a problem.

I have in mothers house a 13A plug on a single area induction hob, flat out it is 2 kW but default on switch on is 1 kW in the main we turn it down from 1 kW only fry up with large pan every needs 1 kW. So 4 rings all used together will likely need around 4 kW max. OK may be rated at 7.5 kW but you simply can't use that much.

In my own house the cooker does have a 3.7 kW heat area when boost is selected, but only thing you can use it for is boiling water, anything else it would burn. So in real terms no problem, both will be fine on a 32A MCB.


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PostPosted: Fri Apr 06, 2018 11:43 pm 
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as an aside
cooking by gas is far cheaper than any other method about half the cost off the most efficient electric alternative
unless you have an industrial set up or planning for years ahead the cost off conversion if more than a few pounds will never be money saving choice
as a life style choice on its own with no saving and possible extra running costs the choice is yours

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PostPosted: Sat Apr 07, 2018 1:51 am 
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big-all wrote:
as an aside
cooking by gas is far cheaper than any other method about half the cost off the most efficient electric alternative
unless you have an industrial set up or planning for years ahead the cost off conversion if more than a few pounds will never be money saving choice
as a life style choice on its own with no saving and possible extra running costs the choice is yours

Are you sure? Gas is a cheaper fuel, however more power is lost.

I watched my daughter boiling an electric kettle then pouring the water into a pan and placing on the gas. Puzzled I asked why, "It's quicker" she said, I replied surely not, gas hob is 5.5 kW and kettle is 2.8 kW the gas is nearly twice as powerful.

So she selects a large pan, fills electric kettle to mark, pours water into pan, fills kettle again, puts lid on pan, and switches both one together. I could not believe the result, kettle took around half the time, so looking at ratings than kettle was around 4 times more efficient than a pan on the gas.

When I got home I repeated the experiment with an induction hob, however this time both boiled together.

So it seems the induction hob can run on a 1/4 of the power needed to run a gas hob, so for gas to compete it needs to be a 1/4 of the price of electric, gas is cheap, but not that cheap.

Then you also must look at other problems, with gas the hob extractor needs to blow the water laden air outside, or the kitchen will get damp, with electric you can use a carbon filter as you are not getting rid of combustion products, this means in winter you use extra gas heating the kitchen, and in summer extra electric to cool the kitchen, or everyone has a helping of the cooks sweat.

Then we look at safety, the gas ring does not auto switch off as you remove the pan, then switch on again as it is returned, so as well as safety of not having an exposed flame, also energy saved as it turns off when not required automatic. As to blowing the corner out of blocks of flats well that's why gas is banned in many flats.

I am sure if some one tried to invent the gas hob today it would bet banned on safety grounds.



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PostPosted: Sat Apr 07, 2018 8:22 am 
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ericmark wrote:
So it seems the induction hob can run on a 1/4 of the power needed to run a gas hob, so for gas to compete it needs to be a 1/4 of the price of electric, gas is cheap, but not that cheap.


https://www.ukpower.co.uk/home_energy/t ... r-unit-kwh

So better than a 1/4


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PostPosted: Sat Apr 07, 2018 8:25 am 
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big-all wrote:
although i think diversity tends to be over the whole house load rather than point loading on a single circuit


Appendix 8.4 of the OSG gives the guidance that a domestic cooker up to 15kW may be used with a 32A supply.



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PostPosted: Sat Apr 07, 2018 8:46 am 
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OnlyMe wrote:
big-all wrote:
although i think diversity tends to be over the whole house load rather than point loading on a single circuit


Appendix 8.4 of the OSG gives the guidance that a domestic cooker up to 15kW may be used with a 32A supply.


15000/230 = 65.2A, you would quickly trip it out.


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PostPosted: Sat Apr 07, 2018 8:54 am 
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Rorschach wrote:
OnlyMe wrote:
big-all wrote:
although i think diversity tends to be over the whole house load rather than point loading on a single circuit


Appendix 8.4 of the OSG gives the guidance that a domestic cooker up to 15kW may be used with a 32A supply.


15000/230 = 65.2A, you would quickly trip it out.


Diversity applies.


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PostPosted: Sat Apr 07, 2018 10:35 am 
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OnlyMe wrote:
Rorschach wrote:
OnlyMe wrote:
big-all wrote:
although i think diversity tends to be over the whole house load rather than point loading on a single circuit


Appendix 8.4 of the OSG gives the guidance that a domestic cooker up to 15kW may be used with a 32A supply.


15000/230 = 65.2A, you would quickly trip it out.


Diversity applies.


That may be but whats the point of having something that big if you can't run it all at once? I have run a double oven and all 4 hot plates at once, not often I concede but I would want that option to be available.

Regarding the OP though, the induction hob needs it's own 6mm supply, the oven though can run off a standard 13amp plug, so that may be an option?


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PostPosted: Sat Apr 07, 2018 10:48 am 
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big-all wrote:
as an aside
cooking by gas is far cheaper than any other method about half the cost off the most efficient electric alternative
unless you have an industrial set up or planning for years ahead the cost off conversion if more than a few pounds will never be money saving choice
as a life style choice on its own with no saving and possible extra running costs the choice is yours


To be honest its not about the cost.. I have a disabled daughter and she struggles lifting the pans when full up the extra height onto the gas ring.. then she has to ensure its balanced on the ring propely.. and she is a messy git, and i am sick of scrubbing the gas hob.. Yes i will have to clean the induction hob, but it has no buttons to get in the way :):)


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PostPosted: Sat Apr 07, 2018 12:13 pm 
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Rorschach wrote:
OnlyMe wrote:

Diversity applies.


That may be but whats the point of having something that big if you can't run it all at once? I have run a double oven and all 4 hot plates at once, not often I concede but I would want that option to be available.


The point is that when you are cooking it's very unlikely that all the plates will be running at the same time. Boil a pan of water and then let it simmer. The plate will be off for most of the time once the water is at boiling temperature.



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PostPosted: Sat Apr 07, 2018 1:41 pm 
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dapex wrote:
big-all wrote:
as an aside
cooking by gas is far cheaper than any other method about half the cost off the most efficient electric alternative
unless you have an industrial set up or planning for years ahead the cost off conversion if more than a few pounds will never be money saving choice
as a life style choice on its own with no saving and possible extra running costs the choice is yours


To be honest its not about the cost.. I have a disabled daughter and she struggles lifting the pans when full up the extra height onto the gas ring.. then she has to ensure its balanced on the ring propely.. and she is a messy git, and i am sick of scrubbing the gas hob.. Yes i will have to clean the induction hob, but it has no buttons to get in the way :):)

i have to mention it as i know people who have been sold "super cheap to run electric radiators" to replace there perfectly functioning gas central heating
and rather than saving money they finished up with a horendous power bill no savings and a heating system they couldn't afford to run :shock: :shock:

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PostPosted: Sat Apr 07, 2018 7:14 pm 
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Rorschach wrote:


That may be but whats the point of having something that big if you can't run it all at once? I have run a double oven and all 4 hot plates at once, not often I concede but I would want that option to be available.



That's where diversity and simmerstats come in.

"I have run a double oven and all 4 hot plates"

Indeed. My Electric range cooker has 5 ceramic plates, 2 ovens and a grill. Total of 13.8 Kilowatts. You can run all of it at once, I often do at Christmas. Never tripped the 32A breaker once.

@ OP you'll want to hard wire your hob into the circuit that is isolated by the main cooker switch. The oven could be put on a 13 A circuit, I would suggest via a 13 Amp SFCU above counter height for easy isolation. That will give you the best of both options.

PS. Get another Electrician in. The one you had clearly either doesn't want the job (because it's too small for him) or doesn't understand your requirements.

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