Electric cooker....just attach a wire?

[scaredofelectricity]

Hello there!
Rather foolishly I bought an electric cooker (completely electric, double oven, four hobs) and was under the impression that you just plug them in.
Oviously now I realise that it's not that simple, but I'm scared of electricity!

I've searched a bit on this forum but not found an answer to my silly question.
Is it just a case of checking the manual and buying the correct cable and fitting it between the cooker and that plate on the wall?

There's a box in the kitchen with a plug socket and a red switch on it that says "cooker", then there's a blank square-socket shaped box thing right behind where the cooker goes.
The delivery man told me that I just need to "hard-wire" the cooker to this box.
I'm fine with fitting the cable between cooker and this square panel, but I'm unsure if all I need to do is get the correct cable or should I be checking for other dangers?
I would happily pay for an electrician to do it but money is very very short after a complicated house move.
I have the manual with specifications for the cooker in there, but I'm unsure what relates to what.
Help?
Please?
Thanks in advance!

 

[ban-all-sheds]

Hello there!
Rather foolishly I bought an electric cooker (completely electric, double oven, four hobs) and was under the impression that you just plug them in.
Oviously now I realise that it's not that simple, but I'm scared of electricity!

I've searched a bit on this forum but not found an answer to my silly question.
Is it just a case of checking the manual and buying the correct cable and fitting it between the cooker and that plate on the wall?

No.

There's a box in the kitchen with a plug socket and a red switch on it that says "cooker",

FYI - that is known as the Cooker Control Unit, or CCU.

then there's a blank square-socket shaped box thing right behind where the cooker goes.

That's the cooker outlet plate.

The delivery man told me that I just need to "hard-wire" the cooker to this box.

In terms of simply connecting it, he's right, but you should check a few things first.

I'm fine with fitting the cable between cooker and this square panel, but I'm unsure if all I need to do is get the correct cable or should I be checking for other dangers?

It's unlikely there will be any actual "dangers".

I have the manual with specifications for the cooker in there, but I'm unsure what relates to what.

Does it not tell you what size cable to use?
Somewhere it should tell you what the total rating of the appliance is in watts (W) or kilowatts (kW). It should also have it on a plate on the back of the cooker near to where the cable attaches.

1) What is that rating?

2) Also, do you have a consumer unit (CU) with circuit breakers (MCBs), or a fusebox with fuses?

3) What is the rating of the MCB or fuse for the cooker circuit?

4) If you can easily see the cable for the cooker circuit where it leaves the CU, can you tell us how big it is?

 

[scaredofelectricity]

Many thanks for the detailed and quick response!
(Not sure why you wish to have all sheds banned though, that's a little bit worrying).

1) What is that rating?

Maximum wattage - 9.8kW
Supply frequency - 50Hz
Supply voltage 230V AC

2) Also, do you have a consumer unit (CU) with circuit breakers (MCBs), or a fusebox with fuses?

I have those trip-switch things that I presume are MCBs.

3) What is the rating of the MCB or fuse for the cooker circuit?

Um, it says 230/400V under the actual trip-switch. Is that what you mean?

4) If you can easily see the cable for the cooker circuit where it leaves the CU, can you tell us how big it is?

Sorry, I can't see it at all.

Does it not tell you what size cable to use?

It says in the manual - "Recommended cross section area is 6mm squared".

Thanks again in advance!

 

[plugwash]

I have those trip-switch things that I presume are MCBs.

yes they are

Um, it says 230/400V under the actual trip-switch. Is that what you mean?

what you are looking for is the current rating of the breaker not the max wokring voltage
you are looking for a figure printed on the breaker like 32A or 40A or 45A or 50A or 63A

Sorry, I can't see it at all.

then you are probablly going to have to open up one of the accessories on the cuircuit

the easiest way to identify cable sizes for amuters imo is to buy a short length of each size and just compre them to your cable

It says in the manual - "Recommended cross section area is 6mm squared".

that depends on a lot of other factors which i will explain when i have the full details on your cuircuit

 

[scaredofelectricity]

Thanks for the help so far, plugwash.

what you are looking for is the current rating of the breaker not the max wokring voltage
you are looking for a figure printed on the breaker like 32A or 40A or 45A or 50A or 63A

It says B32A below the cooker breaker thingy.
(And under the lights it says B6A so I guess this is the right thing that I'm looking for).

Thanks ever so much folks, and sorry for being so bloody green!
They should teach this stuff as a compulsory subject at schools. "Basic life teaching" or something.

 

[ban-all-sheds]

Many thanks for the detailed and quick response!
(Not sure why you wish to have all sheds banned though, that's a little bit worrying).

As in

not

 

[scaredofelectricity]

Many thanks for the detailed and quick response!
(Not sure why you wish to have all sheds banned though, that's a little bit worrying).

As in

not

Ah, I see.
The humble garden shed hasn't upset you, it's the large DIY stores selling potentially lethal weapons to people like me who haven't got a clue how to use them properly.
Is that close to the "ban-all-sheds" thing?
Or not?
Just curious.

 

[plugwash]

at absoloute maximum load that cooker could draw 43A

according to the official diversity rules (10 A + 30% balance + 5 A for socket) your cuircuit must at minimum be rated at just under 20A

however if you want to be able to use everything on your cooker at once this is obviously goign to cause a trip

i strongly suspect your existing cooker cuircuit is wired in 6mm (but you should still check by comparing it with a new peice of 6mm)

in this case it is ok by regs to conenct your cooker to the existing cuircuit with a peice of 6mm twin and earth

however it may be wise to re-run everything in 10mm and use a higher rating of breaker to reduce neusence tripping

 

[ban-all-sheds]

Thanks for the help so far, plugwash.

what you are looking for is the current rating of the breaker not the max wokring voltage
you are looking for a figure printed on the breaker like 32A or 40A or 45A or 50A or 63A

It says B32A below the cooker breaker thingy.
(And under the lights it says B6A so I guess this is the right thing that I'm looking for).

So your cooker circuit has a 32A breaker. Provided it was done properly, that means that the cable feeding the CCU is 6mm as a minimum.

Your cooker's maximum demand will be 42.6A (9800W/230V), which lies between the highest current at which a 32A Type B breaker will never trip (36A) and the one at which it will trip within 1 hour (46A).

However - the rules for calculating the real load of a cooking appliance assume that you do not have everything going flat out at the same time for a long time - if you use the "accepted" calculation, your cooker circuit needs a capacity of 20A, or 25A if the CCU has a socket built in.

There is a constant debate over whether that rule is sensible or not, and given a free hand I think most people here wouldn't use it, but there is no doubt that in real life you do not have all 4 rings and both ovens running flat out all the time. On the assumption that the cooker circuit has 6mm or 10mm cable, then everything checks out.

The question is whether you should assume that whoever installed the electrics did use 6 or 10mm cable for that circuit.....

 

[altec]

Your cooker's maximum demand will be 42.6A (9800W/230V), which lies between the highest current at which a 32A Type B breaker will never trip (36A) and the one at which it will trip within 1 hour (46A).

AT LAST! Somebody who I hope can explain these "design overload characteristics" of MCB's. BR & FWL spoke on such issues before but i could never understand. I think it was meant only for the ears (or should I say eyes) of high fluting electrical engineers.

How did you calculate this where did you get the figers from. Is there much of a variation between manufactures. How severe is this on the MCB’s themselves. Like, if you were to be running then up to max overload limit continually.

Thanks Declan

 

[ban-all-sheds]

I didn't calculate it - I looked it up - there are tables of this sort of info in the wiring regs, although I was using Paul Cook's commentary.

Protective devices have 3 values of interest here:

In: its nominal rating (in this case 32A)
I1: its non-fusing/non-tripping current. For a Type B MCB this is 1.13In
I2: its fusing/tripping current. For a Type B MCB this is 1.45In, and it must trip within 1 hour

So if we have a circuit whose design current (i.e. the current that it is expected to carry in normal use) is Ib, then this should not be greater than the rating of the protective device:

Ib <= In

If Iz is the current-carrying capacity of the cable for continuous service allowing for the way that it has been installed, then this must be no less than the rating of the device:

In <= Iz

Finally, 1.45 times the current carrying capacity Iz of the cable must be no less than I2, the current causing effective operation of the device:

1.45Iz >= I2

So Ib <= In <= Iz

and

I2 <= 1.45Iz.


Or if you prefer pictures:

As for your other questions, I don't know how much the characteristics of MCBs vary - are they allowed to make their I2 operate the device in less than an hour? I don't know.

Running an MCB at or near its limit for long periods wll cause it to overheat, and eventually weaken. But you shouldn't do that - look at the diagram, Ib is lower than all the rest.

 

[scaredofelectricity]

Interesting information - thanks again.
So a 6mm cable should do the job safely provided that whoever fitted the electrics also used the same cable?
Um, scary.


Thanks for all of the help folks.
Sincerely.