Some appliances, such as electric cookers, have a power load greater than 3000W (3kW). These cannot be wired into the ring main because they would overload it. Cookers are generally about 8kW, but there are bigger ones with loadings up to 12kW, which need to be installed on their own 30-amp circuits run in 6mm sq. two-core and earth cable protected by 30-amp circuit fuse.

A cooker with a loading of more than 12kW will need a 45-amp circuit run in 10mm sq. cable and a 45-amp fuse. Each separate radial circuit needs its own fuseway: often in new consumer units there are one or two spares for this purpose, or you can fit an individual switch fuse unit. This will do exactly the same job as your consumer unit, but it will only be 'looking after' one appliance. If you choose the individual switch fuse, choose one with an MCB.

Cooker Control Unit

The cable that supplies power from your consumer unit to the cooker runs to a cooker control unit, fitted within 2m (6ft 6in) of the appliance. This control is a double pole-isolating switch. It must be in easy reach of the cooker, and easily accessible.

One single control unit will serve both parts of a split-level cooker, with cables running to both hob and oven, as long as the control unit is within 2m (6ft 6in) of both. If this isn't possible, then you'll have to install two separate control units. The connecting cables must be the same size as the cables used in the radial circuits and should be sheathed in heat-resistant insulation.

Terminal Outlet Box

Free-standing cookers need to be wired with enough cable to allow them to be moved away from the wall so that you can clean behind. The cable is connected to a terminal outlet box, screwed to the wall about 600mm (2ft) above the floor, while the cable from the terminal outlet box to the cooker control unit is 'fixed'.

• If you are wiring a cooker to a switch fuse unit, you must not connect your meter leads to the electricity company's meter yourself. Contact your electricity supplier who will arrange to test your installation and connect you to the mains if your work is approved.
• If you are in any doubt about installing powerful or large 'non portable' appliances, consult an electrician.