Appendix A — Maximum Demand and Diversity

Some information on the determination of the maximum demand for an electrical installation is provided in this appendix. It also includes some notes on the application of allowances for diversity. It is impossible however, to specify the appropriate allowances for diversity for every type of installation since determination of such allowances calls for special knowledge and experience. The figures shown in Table 8.A.1 are therefore, intended to act as guideline. The current demand of a final circuit is determined by summing the current demands of all points of utilization and equipment in the circuit. Typical values to be used for this summation are given in Table 8.A.2. For blocks of residential dwellings, large hotels, and industrial and large commercial premises, allowances are to be assigned by a competent Engineer. The current demand of a circuit supplying a number of final circuits may be assessed by applying the allowances for diversity given in Table 8.A.2 to the total current demand of all the equipment supplied by that circuit. In the Table, the allowances are appraised either as percentages of the current demand or, where followed by the letters f.l., as percentages of the rated full load current of the current using equipment. After the design currents for all the circuits have been determined, enabling the conductor sizes to be chosen, it is necessary to check that the limitation on voltage drop is met.

Table 8.A.1: Allowances for Diversity

Purpose of final                              Type of Premises
circuit fed from         Individual     Small shops, stores,           Small hotels,
 conductors or           household      offices and business         boarding houses,
 switchgear to          installations,        premises               guest houses, etc.
which diversity     including dwellings
    applies               of a block

1.       Lighting    66% of total current 90% of total current     75% of total current
                     demand               demand                   demand
2. Cooking           10 amperes + 30%      100% f.l. of largest    100% f.l. of largest
  appliances         f.l. of connected     appliance + 80% f.l.    appliance + 80% f.l.
                     cooking appliances    of 2nd largest          of 2nd largest
                     in excess of 10       appliance + 60% f.l.    appliance + 60% f.l.
                     amperes + 5           of remaining            of remaining
                     amperes if socket     appliances              appliances
                     outlet is
                     incorporated in
                     unit.

 Purpose of final                           Type of Premises
 circuit fed from          Individual     Small shops, stores,        Small hotels,
  conductors or            household      offices and business      boarding houses,
  switchgear to           installations,        premises            guest houses, etc.
 which diversity      including dwellings
     applies                of a block

3. Motors (other                          100% f.l. of largest     100% f.l. of largest
   than lift motors                       motor + 80% f.l. of      motor + 50% f.l. of
                           ______
   which are                              2nd largest motor +      remaining motors.
   subject to                             60% f.l. of
   special                                remaining motors
   consideration)
4. Water heater
   (thermostaticall                       No diversity allowable
   y controlled)

Table 8.A.2: Current Demand to be Assumed for Points of Utilization and Current using Equipment

  Point of Utilization or Current-using         Current Demand to be Assumed
                Equipment

15 A socket outlets                         15 A with diversity applied
13 A socket outlets                         13 A with diversity applied

5 A socket outlets                          At least 0.5 A

Protected outlets other than the above      Rated current
mentioned socket outlets

Lighting outlet                             Current equivalent to the connected load,
                                            with a minimum of 100 W per lamp
                                            holder

House hold cooking appliance                The first 10 A of the rated current plus
                                            30% of the remainder of the rated current
                                            plus 5 A if a socket outlet is incorporated
                                            in the control unit

All other stationary equipment /            Standard rated current or nominal current.
Appliances