to the 16th Edition IEE Regulations
   
   
   
 
 

chapter 5
Earthing

chapter 6
Circuits

Circuits
  6.1. - Basic requirements for circuits 6.4 - Industrial socket outlet circuits
  6.2 - Maximum demand and diversity 6.5 - Other circuits
  6.3 - BS1363 socket outlet circuits 6.6 - Circuit segregation


6.5.2 - Cooker circuits

A cooker is regarded as a piece of fixed equipment unless it is a small table-mounted type fed from a plug by a flexible cord. Such equipment must be under the control of a local switch, usually in the form of a cooker control unit. This switch may control two cookers, provided both are within 2 m of it. In many cases this control unit incorporates a socket outlet, although often such a socket is not in the safest position for use to supply portable appliances, whose flexible cords may be burned by the hotplates. It is often considered safer to control the cooker with a switch and to provide a separate socket circuit. The protective device is often the most highly rated in a') installation, particularly in a domestic situation, so there is a need to ensure that diversity has been properly calculated (see Table {6.2}).

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 (see {Chapter 5}).

 

 

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Extracted from The Electricians Guide Fifth Edition
by John Whitfield
Published by EPA Press Click Here to order your Copy

Click here for list of abbreviations