4 mm Cooker circuit 32amp MCB

[ianphilip007]

just visited a customer who requires a 7.3kw hob connected to replace existing gas hob. Currently has a 2.3kw single oven connected to a 4mm T+E cooker radial (ref method c) Protected by a 32amp MCB

i advised that for the hob to be installed the cooker radial would have to be rewired using 6mm T+E as the 4mm was undersized for the load. but having done the calculations and thought about it I'm not quite sure any thoughts.

7.3kw + 2.3kw = Toal Max Load of 9.6KW = 41.7amps

Diversity applied(no socket at cooker switch) 10A + 30% remainder 10+9.51 = 19.51

with diversity applied Ib <In<It

can't find any reference in the regs to a 4mm cooker radial protected via 32amp MCB as the standard is 6mm/32mcb. Not standard circuit arrangement but as 4mmT+E can carry 37 Amps (ref C) I'm thinking that the additional load may be added.

 

[newtothis]

as long as you get the same answer.

Ah great.
I've had my head in the books a lot of late, I was just checkin' I wasn't getting things mixed up LOL

 

[yellowvanman]

i just thought or assumed that 6mm was the minimum cable size allowed for a hob/oven appears i was wrong

this is historical from when BS3036 fuses were used.

ref 433.1.202

 

[specs]

will be fine on 4mm. one reason 6mm is more otfen used is that you're more likely to have some on the van.

As I do, if you ask your wholesaler about 4mm not many stock much and to be honest the price difference isn't that much.

 

[Parker27]

Assuming your customer is replacing their 2.3kw oven with a new 7.3kw hob - why not get the installation instructions of the new 7.3kw oven and see what the manufacturer recommends, if you install anything less than the manufacturer recommends, you are not covering yourself.

 

[cobrauk]

Diversity for stats kicking in and out is great but tell my wife that she will never have all the hobs and ovens on at once lol

I for one always allow for the worse that way we are always covered also we also are having more and more split ovens (2No) and hobs in a lot of installs, these ovens require being fed via separate radials as the ovens my be 20/32amps and the hob only 13amp via a socket not off the cooker circuit.

 

[Engineer54]

Assuming your customer is replacing their 2.3kw oven with a new 7.3kw hob - why not get the installation instructions of the new 7.3kw oven and see what the manufacturer recommends, if you install anything less than the manufacturer recommends, you are not covering yourself.

I'd much prefer to use the 60+ year tried and proved system of cooking appliance diversity, than any manufacturers instructions/recommendations. As stated many times here, for some reason these manufactures work around connected loads, that in many cases, not all of those connected loads can be utilised at once...

 

[Engineer54]

Diversity for stats kicking in and out is great but tell my wife that she will never have all the hobs and ovens on at once lol

I for one always allow for the worse that way we are always covered also we also are having more and more split ovens (2No) and hobs in a lot of installs, these ovens require being fed via separate radials as the ovens my be 20/32amps and the hob only 13amp via a socket not off the cooker circuit.

I bet there isn't many electric hobs out there that are on a 13A plug top, it's normally the oven that comes with a 13A plug top!! lol!!

Hells bells, what sort of domestic oven would need a 32A supply each??

 

[cobrauk]

I bet there isn't many electric hobs out there that are on a 13A plug top, it's normally the oven that comes with a 13A plug top!! lol!!

Hells bells, what sort of domestic oven would need a 32A supply each??

I do not want to say I told you so but check this out and there many more like it ]Hoover HPI430BLA Built In Induction Hob - Black


And I did said 20/32 amps for ovens

 

[Engineer54]

I do not want to say I told you so but check this out and there many more like it ]Hoover HPI430BLA Built In Induction Hob - Black


And I did said 20/32 amps for ovens

I'm still trying to work out how 4 X 1.5KW equaling 6KW (using the lowest stated elements size) suddenly becomes 3KW suitable for connection via a 13A plug top, unless i'm completely missing something that is?? lol!!

Is that for two ovens or one oven??

 

[cobrauk]

I'm still trying to work out how 4 X 1.5KW equaling 6KW (using the lowest stated elements size) suddenly becomes 3KW suitable for connection via a 13A plug top, unless i'm completely missing something that is?? lol!!

Is that for two ovens or one oven??

Its Called Diversity my Dear Watson lol

And if you buy one of these you will only need two sockets
http://ao.com/product/HOC7096X-Hoov...&WT.z_AG=pla&gclid=COmG893yosQCFSrMtAodqA0AAQ

 

[Engineer54]

Its Called Diversity my Dear Watson lol

And if you buy one of these you will only need two sockets
Hoover HOC709-6X Built In Electric Single Oven - Stainless Steel

Me thinks that 13A fuse will be blown before the diversity has a chance to kick in!! lol!!

Yeah, plug em both into a ring circuit, sounds about right!!

 

[nickblake]

Alot of the hob and cooker manufacturers now stipulate 4mm to wire the cookers in ,from the connection plate that is

 

[Paul508]

I have just been asked to look at a new double cooker install, the installer has connected the oven by 6mm to a 45A cooker switch and then connected the switch via 4mm to a socket on a 4mm radial protected by a 32A RCBO. Now I expect the RCBO to suitably protect the circuit but has anyone else seen this setup before?

 

[LastManOnline]

I have just been asked to look at a new double cooker install, the installer has connected the oven by 6mm to a 45A cooker switch and then connected the switch via 4mm to a socket on a 4mm radial protected by a 32A RCBO. Now I expect the RCBO to suitably protect the circuit but has anyone else seen this setup before?

Never. First observation is that it's unlikely it was installed by a conventionally trained electrician.A cooker should have its own circuit. Most countries would require it (can, t speak for UK) And if it is allowed, it is terribly poor design.
. Next obvious question is... Is it unsafe? Well like you I would have to conclude that technically the circuit is protected from overload by the 32 amp rcbo. But this has the potential to be a very heavily loaded circuit and cause inconvenience depending on what other appliances are in circuit.

 

[Paul508]

Thank you LastManOnline, it was installed by a B&Q kitchen fitter. It is on the same circuit as a washing machine, a freezer and a kettle so I think using diversity it’s within the scope of the RCBO but I think I will err on the safe side and get an electrician to check it