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
