Replacing old electric cooker

[sannesley]

I currently have an electric hob (with a nice big crack right the way through it ) and a double electric under oven built in. Because of the cracked hob we're replacing the whole lot, hob and under oven.

I'm asuming that it should be as simple to do as the steps below:

1. turn off electricity supply at mains
2. take out old hob and under oven
3. put in new hob and under oven rewring to existing connections
4. turn mains electric back on.

Have I missed anything or should these steps do the trick?

 

[Chri5]

Sounds ok from the fit viewpoint.

I would suggest you google your old units for wattage, then compare that with the new units wattage.

Reason being that you do need to confirm that your existing fuse and cable size between fuse and appliances is up to the job.

Once you have the new load, say 11kw for induction hob and 6kw for oven you then calculate the load in amps.

ie 1kw = 1000w, divide the total wattage of both appliances by 230v to get the amp load.

If that amp load is greater than the existing fuse you have a problem, as in new fuse and new cabling likely.

 

[sannesley]

I've just learned that any cooker with a rating higher than 7.2Kw will require a 45 amp fuseway.

 

[Steve]

I've just learned that any cooker with a rating higher than 7.2Kw will require a 45 amp fuseway.

You just learned wrong Where did you "learn" this?

 

[sannesley]

on this very site //www.diynot.com/pages/el/el027.php.

At the consumer unit, the cooker will require its own fuse way. A 30amp fuseway can support an appliance of up to 7.2kw providing that the control unit does not also have a socket outlet. For higher powered appliances a 45amp fuse or greater is required. The control unit is then connected to the consumer unit by a radial circuit.

7.2kw = 7200 watts. UK voltage is 230V. 7200 / 230 = 31amps

That would be about right. Granted that strictky 7kw would be the upper limit for a 30amp fuseway.

 

[sannesley]

A quick look in the electrolux website has shown the following:

double under-oven output - 4.9-5.3kw
hob which model I'm not 100% sure yet but as a rough guide - 8.1kw

adding these together = 13.4kw

calculating the ampage this would draw down:

13400/230= 74amps



What size of fuse would that require?

I'll have to check out the specs of the existing oven and hob tonight to see their ratings and compare it with the figures above.

 

[Steve]

Given you wont be using everything at once, and the elements cycle on and off on thermostats, a 40A fuse / MCB will be enough.

 

[sannesley]

Just a quick question, but when people talk about 4mm and 6mm wire for radial circuits for a cooker as I understand it they get those dimensions for the wire by measuring its height with the wire on its flat side?

 

[disinfo]

Just a quick question, but when people talk about 4mm and 6mm wire for radial circuits for a cooker as I understand it they get those dimensions for the wire by measuring its height with the wire on its flat side?

No, the measurement comes from the CSA of the individual conductors.

 

[hairyben]

Once you have the new load, say 11kw for induction hob and 6kw for oven you then calculate the load in amps.

ie 1kw = 1000w, divide the total wattage of both appliances by 230v to get the amp load.

If that amp load is greater than the existing fuse you have a problem, as in new fuse and new cabling likely.

Like Steve says this is incorrect, diversity is applied to cooker circuits as they're never fully loaded, 40A is ample for 99% of domestic electric cookers.

In fact, just did a periodic on a house with a 4 ring ceramic hob & elec oven on a 16A MCB, while this is pretty shoddy, in 5 years they've not had a problem- guess they never use more than two items (2 rings/ ring+oven) at once.

Off the top of my head, whats the diversity calc for cookers? 10A + 30% of balence + 5A if s/o fitted?

 

[ban-all-sheds]

on this very site //www.diynot.com/pages/el/el027.php.

At the consumer unit, the cooker will require its own fuse way. A 30amp fuseway can support an appliance of up to 7.2kw providing that the control unit does not also have a socket outlet. For higher powered appliances a 45amp fuse or greater is required. The control unit is then connected to the consumer unit by a radial circuit.

Oo-err.

Who wrote that, then?

 

[sannesley]

on this very site //www.diynot.com/pages/el/el027.php.

At the consumer unit, the cooker will require its own fuse way. A 30amp fuseway can support an appliance of up to 7.2kw providing that the control unit does not also have a socket outlet. For higher powered appliances a 45amp fuse or greater is required. The control unit is then connected to the consumer unit by a radial circuit.

Oo-err.

Who wrote that, then?

As it looks like a special guide for the installation of an electric cooker rather than some post in a thread started by a member I can only assume that it was written by someone who knows what they're talking about.

I checked and the current double oven and hob combination could draw a maximum of 11.26kw max which works out at requiring a 48amp RCD, There is a 32amp RCD installed and there has never beena problem with the electricity supply when using the current cooker.

Unless anyone knows better I'd be incline to run the new cooker and hob setup on the existing 32amp RCD and only upgrade to a higher ampage if the coooker starts tripping the supply when in use.

 

[ban-all-sheds]

As it looks like a special guide for the installation of an electric cooker rather than some post in a thread started by a member I can only assume that it was written by someone who knows what they're talking about.

I checked and the current double oven and hob combination could draw a maximum of 11.26kw max which works out at requiring a 48amp RCD, There is a 32amp RCD installed and there has never beena problem with the electricity supply when using the current cooker.

Standard diversity guidelines for a "48A" load gets you an assumed demand of 21.4A, or 26.4A if the CCU has a socket.

Unless anyone knows better I'd be incline to run the new cooker and hob setup on the existing 32amp RCD and only upgrade to a higher ampage if the coooker starts tripping the supply when in use.

A sound plan, particularly as upping the MCB will mean replacing the cable.

When you've got the cooker installed, and it's working fine normally, do a "stress test" - fill the largest heaviest pans and casseroles you have with cold water and put them on the hob and in the ovens, turn all the rings on to max and the ovens/grills as well, and see what happens....