Old cooker split into two.

[TheAlarmMan]

Kitchen is being redone there's already a free standing electric oven and hob that's being binned and the new oven being moved 2m, new oven says 5.1kw total, not sure yet what electric hob is.

Oven is http://www.ikea.com/ms/en_GB/pdf/kitchen_instructions/framtid_dov8_2_double_iu.pdf

Old cooker has cooker isolator and cooker connection point. Unsure cable diameter yet.

Electrician says connect hob to cooker outlet then extend the cable over to the oven?

This to me doesn't sound right, for a start if the isolator does have 6mm and he puts another in the terminal needs to be 12mm?

If the oven is 5.1kw and the hob is say 6kw, 46A?

I'm thinking oven needs to be run back to CU with it's own RCD/MCB?

It's a bit late and it's bucketing down to go to the garage to check the RCD/MCB rating but I know it has it's own.

What do we think?

 

[ban-all-sheds]

We think we'd like to know what sort of "electrician" you have, but that basically if you already have a cooker circuit it can continue to be used and you should leave your electrician in peace to do his job as he probably understands diversity.

 

[TheAlarmMan]

We think we'd like to know what sort of "electrician" you have,

Not sure what you mean by that, I didn't know an electrician so I found one is the local directory.
But it didn't sound right to me, hence why I'm here.

Scenario is Christmas dinner all rings burning both ovens on full tilt, cable getting toastie warm. Fire brigade pop in to put the kitchen out, etc.... Meanwhile sparky's nowhere to be seen.

Thought I'd get a bit more than leave him to his job.

 

[EFLImpudence]

Scenario is Christmas dinner all rings burning both ovens on full tilt,

The voltage will likely be a bit lower so you'll be alright.

It would be all over the news if it happened.

 

[JohnW2]

Scenario is Christmas dinner all rings burning both ovens on full tilt, cable getting toastie warm. Fire brigade pop in to put the kitchen out, etc.... Meanwhile sparky's nowhere to be seen.

There are two things you need to understand, both of which your electrician will presumably have taken into account:

1...Even with all rings and both ovens 'on full tilt', there will very rarely, if ever, all be drawing electricity (at their maximum load) simultaneously - all are thermostatically controlled, the thermostat switching them on and off as required to maintain the desired temperature, and you'd probably be surprised how often each of them is 'off' once they are up to temperature.

Hence the concept of 'diversity' used when designing circuits, which takes on board this concept that not everything will be drawing current simultaneously, at least not for significant periods. For a cooking appliance, the rule is that one should design a circuit to provide the first 10A of current plus 30% of the amount by which the maximum possible current draw of the appliance exceeds 10A. Your ovens+hob amount to about 48A maximum at 230V. Hence, the circuit would be designed to safely carry 10A plus 30% of (48A-10A=38A), which is about 21.4A.

2...Both the MCB and cable can carry considerably more than their 'rated' amounts of current for substantial periods of time. A 32A MCB will carry a current of about 45A for an hour (and 50A for at least 15 minutes)before tripping, and the correspondingly sized cable (at least 4 mm²) can safely carry that current for at least that long. Hence, even for those very brief periods that your ovens+hob might conceivably draw the full 48A, no harm will result,and the Fire Brigade won't be required!

Hope that helps to explain.

Kind Regards, John

 

[TheAlarmMan]

Thanks John,

It's strange I got a call from this chap last night and he's now decided that the cooker should have it's own 6mm cable run back to the CU with it's own 32a breaker.

Concerned now he's doesn't know what he's doing!

 

[JohnW2]

Thanks John, It's strange I got a call from this chap last night and he's now decided that the cooker should have it's own 6mm cable run back to the CU with it's own 32a breaker.

Isn't that probably what your existing 'old cooker circuit' is?

Concerned now he's doesn't know what he's doing!

See above.

Kind Regards, John

 

[TheAlarmMan]

That is what's in already but I'm splitting the existing single appliance into 2 separates 2m apart.

 

[JohnW2]

That is what's in already but I'm splitting the existing single appliance into 2 separates 2m apart.

Yes, I realise that. Do you mean he's now planning to put in a second 32A circuit - then use one 32A circuit for the oven and the other 32A circuit for the hob?!

Kind Regards, John

 

[TheAlarmMan]

Sorry yes that's correct.

 

[JohnW2]

Sorry yes that's correct.

Well, provided that the instructions of neither oven nor hob require protection less than 32A, no-one could fault that - but, per what I explained before, it could be argued that having two 32A circuits for a cooker (oven+hob) is a bit unnecessary/'OTT'!

Kind Regards, John

 

[TheAlarmMan]

OTT I can cope with, smoke I can't!

But seriously, even with diversity, my first thought would have been to have 2 feeds, he's just confirmed that.

In fact I might just go get the cable to and..........DIY!!

 

[ban-all-sheds]

OTT I can cope with, smoke I can't!

With a single circuit the only smoke you'll get will be from your cooking. Having 2 circuits won't prevent that.

But seriously, even with diversity, my first thought would have been to have 2 feeds,

Why?

he's just confirmed that.

He doesn't seem to know what he's doing.

In fact I might just go get the cable to and..........DIY!!

I wouldn't advise that - you don't know what you're doing either, and having been told about diversity you say you don't want to know about it.

Plus you'd have to go through the process of applying for and getting Building Regulations approval before you could start.

 

[TheAlarmMan]

OTT I can cope with, smoke I can't!

With a single circuit the only smoke you'll get will be from your cooking. Having 2 circuits won't prevent that.

But it will split the load across the two cables, so if the original cable is say sandwiched between rockwool, buried or otherwise halving the rated capacity it wont cause an issue.

But seriously, even with diversity, my first thought would have been to have 2 feeds,
Why?

So that if both devices were being run at full capacity, the single cable would be nowhere near it's rated capacity.

In fact I might just go get the cable to and..........DIY!!

Have you ever heard of irony? Hence this being the "DIYnot" forum. I was attempting to make a small joke.

I wouldn't advise that - you don't know what you're doing either, and having been told about diversity you say you don't want to know about it. Plus you'd have to go through the process of applying for and getting Building Regulations approval before you could start.

Where did I say I didn't want to know about diversity?


I asked this question for guidance, I do not know ALL the 17th ed, BS and PP regs and since I have not used this electrician before and I wasn't convinced he had the right idea. I came here to ask the question.

You know what BAS, I'm unsure why your so off?
Do you have some kind of complex where if someone doesn't know what you know you have to attempt to belittle them rather than offering sensible advice? Or are you one of those who has to post to get their total posts up.

You know I'm not interested.

JohnW2 thanks for all your info, it was most helpful.

 

[ban-all-sheds]

But it will split the load across the two cables, so if the original cable is say sandwiched between rockwool, buried or otherwise halving the rated capacity it wont cause an issue.

If cables are installed that way then they should have their size increased or their protective device decreased to account for their drop in current carrying capacity.

Installing cables with Iz < Iz is not allowed.

But then you know that, apparently.

So that if both devices were being run at full capacity, the single cable would be nowhere near it's rated capacity.

You've currently got an oven and hob on one cable, which presumably has never caught fire.

You plan to install an oven and a hob but are worried that one cable will catch fire.

I was attempting to make a small joke.

Sorry - it can be hard to spot humour.

Where did I say I didn't want to know about diversity?

You asked if a single cable would be OK on the basis of a calculation not using diversity.

You were told about diversity and came back with a concern about cables catching fire.

JohnW2 (who you thanked for useful info) told you about diversity again.

And still you proposed to take no account of it in your design.

I asked this question for guidance, I do not know ALL the 17th ed, BS and PP regs and since I have not used this electrician before and I wasn't convinced he had the right idea. I came here to ask the question.

When he proposed putting both appliances on one circuit you weren't happy.

When he proposed doing the same as you said you would, and put them on 2 circuits, you weren't happy.

You know what BAS, I'm unsure why your so off?

I'm not.

Do you have some kind of complex where if someone doesn't know what you know you have to attempt to belittle them rather than offering sensible advice?

I am not belittling you - just observing that you don't really know what you are doing and therefore offering the sensible advice that you should not be DIYing.