1. Voltage drop at 50 Hz of multicore cables
with circular copper conductors
Vc at 50 Hz in mV/A.m
Conductor Size at a conductor temperature of 75 °C
in mm2 1Φ Value 3Φ Value
1 51.63 44.7
1.5 33.03 28.6
2.5 18.02 15.6
4 11.22 9.71
6 7.5 6.49
10 4.46 3.86
16 2.81 2.43
25 1.78 1.54
35 1.28 1.11
These figures are based on Table 42 of AS3008. 1.
lΦ value = 3Φ value x l.155

5. Vd = Vc x L x I
1000
Vd = 2.43 x 20 x 60 = 2.916 Volts
1000
Voltage drop in mains on a three-phase 400
volt basis = 2.916 Volts.

6. Vd = Vc x L x I
1000
Vd = 4.46 x 30 x 50 = 6.69 Volts
1000
Voltage drop in final sub-circuit on a single-
phase 230 V basis = 14.5 volts.

7. Vd = 2.916 + (6.69x1.732)
Vd = 2.916 +11.59 =14.5 V on a three-phase
400 V basis.
Answer: Voltage drop = 14.5 V on a three-
phase 400 V basis.

8. 2.916
Vd = ( )+ 6.69 = 1.68+ 6.69 = 8.37 V
1.732
Answer: Voltage drop = 8.37 V on a single-
phase 230 V basis.

9. Three-phase mains voltage: 5% of 400 = 20 V
Single-phase voltages: 5% of 230 = 11.5 V

10. Voltage drop in mains x 100 = % of allowable total voltage drop
20
2.916 x 100 = 14.58 % of allowable total voltage drop for mains.
20

11. Voltage drop in final sub-circuit x 100 = % of allowable total voltage drop
20
6.69 x 100 = 58.17% of allowable voltage drop for final sub-circuit.
11.5

12. Total voltage drop = 14.58 + 58.17
Total voltage drop = 72.75%
Converting to a three-phase 400 V value
72.75 x 20 = 14.5 Volts on a three-phase 400 V basis
100
Answer: Voltage drop = 14.5 Volts on a three-phase
400 V basis.

13. Total voltage drop = 14.58 + 58.17
Total voltage drop = 72.75%
Converting to a single-phase 230 V value
72.75 x 11.5 = 8.37 Volts on a single-phase 230 V basis
100
Answer: Voltage drop = 8.37 Volts on a single-phase
230 V basis