16th Edition (reference only) – NOW superseded by the 17th Edition IEE Regulations.
 chapter 1 The IEE Regulations chapter 2 Installation Requirements and Characteristics chapter 3 Installation Control and Protection chapter 4 Cables, Conduits and Trunking chapter 5 Earthing chapter 6 Circuits chapter 7 Special Installations chapter 8 Testing and Inspection chapter 9 Data cabling and Networks
 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
 6.2.1 -  Maximum demand 6.2.2 - Diversity 6.2.3 -  Applied diversity

6.2.3 -  Applied diversity

Apart from indicating that diversity and maximum demand must be assessed, the
Regulations themselves give little help. Suggestions of values for the allowances
for diversity are given in {Table 6.2}.
Distribution boards must not have diversity applied so that they can carry the total load connected to them.

Example 6.1
A shop has the following single-phase loads, which are balanced as evenly as possible across the 415 V three-phase supply.

2 x 6 kW and 7 x 3kw thermostatically controlled water heaters
2 x 3 kW instantaneous water heaters
2 x 6 kW and 1 x 4 kW cookers
12 kW of discharge lighting (Sum of tube ratings)
8 x 30 A ring circuits feeding 13 A sockets.

Calculate the total demand of the system, assuming that diversity can be applied. Calculations will be based on {Table 6.2}.

The single-phase voltage for a 415V three-phase system is 415/Ö 3 = 240 V.

All loads with the exception of the discharge lighting can be assumed to be at unity power factor, so current may be calculated from

 l = P U

Thus the current per kilowatt will be

 1000 A = 4.17 A 240

 Table 6.2 - Allowance for diversity Note the following abbreviations : X is the full load current of the largest appliance or circuit Y is the full load current of the second largest appliance or circuit Z is the full load current of the remaining appliances or circuits Type of final circuit Type of premises Households Small shops, stores, offices Hotels, guest houses Lighting 66% total demand 90% total demand 75% total demand Heating and power 100% up to 10 A + 50% balance 100%X + 75%(Y+Z) 100%X + 80%Y + 60%Z Cookers 10 A + 30% balance + 5 A for socket 100%X + 80%Y + 60%Z 100%X + 80%Y + 60%Z Motors (but not lifts) 100%X + 80%Y + 60%Z 100%X + 50%(Y+Z) Instantaneous water heaters 100%X + 100%Y + 25%Z 100%X + 100%Y + 25%Z 100%X + 100%Y + 25%Z Thermostatic water heaters 100% 100% 100% Floor warming installations 100% 100% 100% Thermal storage heating 100% 100% 100% Standard circuits 100%X + 40%(Y+Z) 100%X + 50%(Y+Z) 100%X + 50%(Y+Z) Sockets and stationary equip. 100%X + 40%(Y+Z) 100%X + 75%(Y+Z) 100%X + 75%Y + 40%Z

Water heaters (thermostatic)

 No diversity is allowable, so the total load will be: (2 x 6) + (7 x 3) kW = 12 + 21kw = 33kw This gives a total single-phase current of I = 33 x 4.17 = 137.6 A

Water heaters (instantaneous)

 100% of largest plus 100% of next means that in effect there is no allowable diversity. Single-phase current thus = 2 x 3 x 4.17 = 25.0 A

Cookers

 100% of largest = 6 x 4.17A = 25.0 A 80% of second = 80 x 6 x 4.17A = 20.0 A =100 60% of remainder = 60 x 4 x 4.17 A = 10.0 A =100 Total for cookers = 55.O A

Discharge lighting

 90% of total which must be increased to allow for power factor and control gear losses. Lighting current = 12 x 4.17 x 1.8 x 90 = 81.1 A 100

Ring circuits

 First circuit 100%, 50 current is 30 A 75% of remainder = 7 x 30 x 75 = 157.5 A 100 Total current demand for ring circuits = 187.5 A Total single phase current demand = 486.2 A Since a perfect balance is assumed, three phase line current = 486.2 A =3 = 162 A

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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