Robbie,
Here is the formula in calculating Voltage Drops in Three Phase Circuits:
Three Phase Formulas as Follows:
%VD,3PH= KFactorxAmpsxLength of CCT in Metres
Phase to Phase Supply Voltage-volts
Single Phase Formulas as Follows:
%VD,1PH= KFactorx1.15xAmpsxLength in Metres
Phase to Neutral Supply Voltage
If you are using the OESC 2002'look under Table D3.
For other nominal voltages, multiply the distances in metres by the other nominal voltage (in volts) and divide by 120.
Example on use of Table:
Consider a two conductor circuit of No. 12 AWG copper NMD90 carrying 16 A at nominal 240 V under maximum ambient of 30°C. The maximum run distance from the centre of distribution to the load without exceeding a 3% voltage drop is:
Maximum run length for No. 12 AWG, 16 A, 1% voltage drop at nominal 120 V from Table is: 6.1 m
Distance Correction Factor to be used is:
From Table 2, allowable ampacity for 2
conductor No. 12 AWG NMD90 (90°C rating per Table 19) is 20 A. The given current is 16 A or 80% of the allowable ampacity.
The Distance Correction Factor to be used, from Note (3), 90°C row, 80% column, is 1.00.
The maximum run length is:
6.1 m x 3% x 1.00 x 240v = 37m
120v
Beyond this distance a larger size of conductor is required, ie, No. 10 AWG (30 A allowable ampacity) beyond 37 m up to and including 62 m.
9.7 ,m x 3% x 1.06 x 240v = 62m
120
Tony Moscioni
Electrical Inspector
Electrical Safety Authority
