Electrical Instruments

Electrical Calculations in South Africa

In South Africa voltage is generally measured 230Volt AC (alternating current) at a frequency of 50Hz (pulses per second) phase to neutral in single phase installations and 400Volt AC at 50Hz phase to phase in three phase installations.

For the purposes of the calculations on this page we will be using 60Ampere as our load.

Take note that there are still suburbs & towns in South Africa that use 220Volt AC single phase and 380Volt AC three phase. Find out from your local authorities what voltage is supplied to your specific town or suburb before you make the calculation

General Electrical Calculations - Single Phase

Volts = Watt ÷ Ampere
Volts = Ampere x Ohms
Ampere = Volts ÷ Ohms
Ampere = Watt ÷ Volts
Ohms = Volts ÷ Ampere
Volt-Ampere (VA or Watt) = Volts x Ampere

Calculate KVA (Kilovolt-Ampere)

Single Phase

KVA = (Volts x Ampere) ÷ 1000
  = (230 x 60) ÷ 1000
  = 13.8KvA

Three Phase

When calculating KvA in a 3-phase installation a factor of 1.73 is introduced (√3 = 1.73)

KVA = (Volts x Ampere x 1.73) ÷ 1000
  = (400 x 60 x 1.73) ÷ 1000
  = 41520 ÷ 1000
  = 41.52 KVA

Calculate Ampere when KVA is known

Three Phase

KVA = (Volts x Ampere x 1.73) ÷ 1000
41.52 KVA = (400 x A x 1.73) ÷ 1000
41.52 x 1000 = 400 x A x 1.73
41520 ÷ (400 x 1.73) = Ampere
41520 ÷ 692 = 60 Ampere

Calculate KW (Kilowatt)

Calculating Kilowatts is slightly more complicated in that the formula includes a value for power factor. The power factor is a nebulous but nevertheless required value that is different for each individual electrical device. If it is not specifically known you may use a value of 0.85 which is generally accepted to be a good average and we will use it in the calculations below.

Single Phase

KW = (Volts x Ampere x Power Factor) ÷ 1000
  = (230 x 60 x 0.85) ÷ 1000
  = 11730 ÷ 1000
  = 11.73 KW

Three Phase

KW = (Volts x Ampere x Power Factor x 1.73) ÷ 1000
  = (400 x 60 x 0.85 x 1.73) ÷ 1000
  = 35292 ÷ 1000
  = 35.29 KW

Convert Between Kilowatt and KVA

The only difference between KW and KvA is the power factor. KvA is always higher than KW.

KW ÷ 0.85 = KVA
KVA x 0.85 = KW