Oven - 20amp fuse - 4mm Cable

[fox33]

Hi all,

I'm in the process of replacing our kitchen, and need a little bit of guidance on the Oven.

We had an electric oven and a gas hob. The intention is to swap the gas hob for an elctric ceramic one.

Now, the cable runs from a 20amp fuse (old wire type) at the consumer unit, through the wall and into a cooker control switch with single socket. Then this goes to the cooker terminal outlet and feeds another single socket next to it for the hob.

The cable run is no more than three meters, and is in 4.0mm cable.

Obviosuly this depends on the model of oven and hob she would like to buy, but is it ok to run both oven and hob this way? Is it likely I'll need to up the fuse to 30amp?

The oven will be into the outlet, and the hob into the spur next to it

 

[Chri5]

Fox

You have had 40+ view and no one has answered your question.

Reason is that there are too many if's and but's. You need to have a firm idea of the hob and oven type and the kw or watt levels they will use.

On the face of it, which is only an educated guess I would suggest updating the fue to 30/32 amp which a 4mm cable over the distance you mention will be fine.

Diversity can be applied to cookers which is a calculation that both units will not be on 100% full tilt, 100% of the time.

Once you know the output in watts divide by 230v to get the amps figure.

Then use the detail below:-


Table 6.2 - Allowance for diversity

Cookers 10 A + 30% balance + 5 A for socket


The diversity applicable to the current demand for a cooker is shown in {Table 6.2} as 10 A plus 30% of the remainder of the total connected load, plus 5 A if the control unit includes a socket outlet. A little thought will show that whilst this calculation will give satisfactory results under most circumstances, there is a danger of triggering the protective device under some circumstances. For example, at Christmas it is quite likely that both ovens, all four hotplates and a 3 kW kettle could he simultaneously connected. Just imagine the chaos which a blown fuse would cause! This alone is a very good reason for being generous with cable and protective ratings.

Example 6.2
A 240 V domestic cooker has the following connected loads:

top oven 1.5 kW
main oven 2.5 kW
grill 2.0kw
four hotplates 2.0 kW each

The cooker control unit includes a 13 A socket outlet. Calculate a suitable rating for the protective device.

The total cooker load is 1.5 + 2.5 + 2.0 + (4 x 2.0) kW = 14 kW

Total current = P = 14000 A = 58.3A
U 240==



The demand is is made up of:

the first 10 A = 10.0 A
+ 30% of remainder = 30 x (58.3 - 10) = 30 x 48.3 = 14.5 A
100 100
+ allowance for socket outlet = 5.O A
total = 29.5 A

A 30 A protective device is likely to be chosen. The cable rating will depend on correction factors

 

[ban-all-sheds]

The intention is to swap the gas hob for an elctric ceramic one.

If you don't do that (and sticking with gas would be much more sensible), you won't have supply problems for just an oven.

 

[Risteard]

U 240==

U = 400V.

Uo = 230V (not 240V).

Uoc could be taken as 240V.

 

[davelx]

Chris5 wrote

On the face of it, which is only an educated guess I would suggest updating the fue to 30/32 amp which a 4mm cable over the distance you mention will be fine.

The OP said that he has rewireable fuses.

4.00mm^2 cable is only rated at 26.8A (37 * 0.725) max. when protected by a 3036 rewireable fuse with no other derating factors, so you cannot uprate the fuse to 30A. That would require 6.0mm^2 cable with no other derating factors in effect.

 

[Chri5]

The OP said that he has rewireable fuses.

How's about

£10 v new run of 6mm ! EIC required !

 

[ban-all-sheds]

How about replacing (or adding a new) CU, new cables of a decent size, radials for appliances e.g. F/F on its own, boiler on its own, a 16A one for an oven, a 16A one for a combi microwave, a 32A one for a hob, a 25 or 32A one for other appliances and sockets, and no more f*rting around with rewirable fuses, plug-in breakers and cables and circuits which are not really suitable?

 

[fox33]

Right, sorry for the slow response!

New oven and hob purchased.

Oven is rated at 3.4 kW – (Single fan oven with grill)
Hob is 6 kW - (four hotplates, two 1.2 kW and two 1.8 kW)

I intend to run the hob from the existing cooker feed, and swap the 20A re-wire for a 30A push in MCB - (after closer inspection the wiring is actually 6mm) this will be wired from the cooker outlet in 6mm

The oven will be wired to a spare slot in the CU, with a 15A MCB.

What switch does the new 15A cooker feed need? I presume a single cooker switch? I also presume, as well as the hob I need to have this accessible above the work top?

I wish I’d bought a standard fan oven under 3kW now; we never use the grill anyway!


Although going on what Chri5 has said above…?

Oven – 3.4 kW
Hob – 6 kW

Total load 3.4 + 6.0 = 9.4kW

Total current = 9.4 kW = 39.2A

10A (First 10A)
8.76A (30% of remainder)
5A (Socket)

Total = 23.76A

Surely doing it this way, I would still need an inline 15A fuse/MCB to the oven?

I suppose I’ve answered my own question here, it can be done as above but I’ve already worked out what the best solution would be!?

A new CU is sadly not an option at the minute, although will definitely get done in the future

 

[1john]

The oven needs a new, individual circuit with a 16A OCPD.

How have you determined the cable size? Are you certain that cable is 6.0mm if it is older stuff with a three stranded earth it could easily be an equivilant to 2.5mm, it is just that all the strands make it appear like is has alot larger csa. Measuring across the sheath will give very little indication of the cable size.

 

[ban-all-sheds]

fox33 - you should read this:

//www.diynot.com/wiki/electrics:part-p

 

[riveralt]

If you have 30Amp MCB(Wylex plug in) at Consumer Unit and 6mm cable from the Consumer Unit to the Cooker Switch (with socket)..... then from the Cooker switch run 6mm to this cooker connection unit

http://www.alertelectrical.com/prod/1022/click-45a-easyfit-dual-appliance-outlet-plate

Then one cable to the oven and the other to the hob.

Incidentally we now use 230v to determine the Amps - which equates to 24.26Amps after diversity.

Note you should be guided by what the manufacturers instructions say with regard to cable sizes to the cooker connection unit - sometimes they quote the power of the oven based on 240v whereas the 17th edition is based on 230v - so perhaps your oven is not so powerful as you think

Oh and because you will be altering the circuit you will need to get your local building control involved or hire an electrician who can sign of his/her own work for half the price.