Voltage Drop

Whatever or how perfect the conductivity of a cable, we will still faced a voltage drop problem caused by natural characteristics, which the impedance exist along the cable when convey currents. Based on certain resource, the voltage drop from the origin source must not be more than 4% of the supply.

Consequently, if we need to deliver supply to long distance, voltage drop calculation must be considered. This will help us to choose the appropriate cable’s size for our design, and to avoid the voltage drop more than 4%.

For this topic, I have approached formulas for the appropriate calculation on voltage drop. What I can conclude from this study is shown below:

VOLTAGE DROP

• Cause by impedance exist in cable
• Can be ignored if the cable length is short

Maximum voltage drop tolerate is 4%:

(a)    For three phase = 415 x 0.04 = 16.6V

(b)    For single phase = 240 x 0.04 = 9.6V

Voltage Drop = (M.D x D x mV/A/m)

                                        1000

Where:    M.D is Maximum Demand (Ampere)

                 D is Distance (meter)

mV/A/m is milivolts / A / meter which is cable impedance value obtain from IEE cable voltage drop Table

 

 Voltage drop from EMSB to ESSB-LP:

               Maximum Demand (MD)      =           600A

               Distance (D)                           =          30m

   mV/A/m                              Z =          0.175 mV/A/m

          (for 4/1C 400mm2 XLPE/PVC cable. Refer to Table4E1B)       

Voltage Drop      = (MD x D x mV/A/m)

                                            1000

                           = 600A x 30m x 0.175

                                             1000

                            = 3.15V

% Voltage Drop  = 3.15V x 100

                                   415V

                            = 0.76%

Voltage drop from ESSB-LP to SUBMAIN 5:

               Maximum Demand (MD)  =           200A

               Distance (D)                       =          75m

mV/A/m                             Z =          0.45 mV/A/m

(for 1 x 4C 95mm2 XLPE/ PVC cable. Refer to Table4E1B)

Voltage Drop      = (MD x D x mV/A/m)

                                            1000

                              = 200A x 75m x 0.45

                                             1000

                              = 6.75V

% Voltage Drop = 6.75V x 100

                                             415V

                              = 1.626%

IEE Wiring Regulations (17th Edition)