Voltage drop Equation

[NickParker]

Which one of the following equation to be used for three phase voltage drop calculations. I believe the equation (1) is more accurate than (2). Why do some literature mentions the equation (2) to calculate voltage drop. Is equation (2) applicable for only for some restricted applications, if so what are the applications?

1)

or

2)

 

[7anoter4]

The no.1 it is more accurate than no.2, in any way.
However, if a.c.R/X>=7 the error will be less than 1%[as for copper conductor cross section area less than #4]
By the way,there is a more accurate formula for voltage drop [See IEEE 141/1993 3.11 Calculation of voltage drops]

 

[NickParker]

On reading further, another equation is,

VD = (mV/A/mtr x length x Current x PF)/1000

 

[7anoter4]

If you intend to follow BS7671 Appendix 4 chapter 6 TABLES OF VOLTAGE DROP, at first this formula it is for cross section less than 16 mm^2. For more than 16 mm^2 the
recommended equation it is close to your no.1.
However a factor Ct [very sophisticate in my opinion] has to be employed as temperature correction factor.
Then, for cable cross section area of 16 mm^2 or less:
VD=Ct*cos(Φ)*[mV/A/m]/1000 [V] and for more than 16 mm^2:
VD=Ct*[mVr/A/m*cos(Φ)+mVx/A/m*sin(Φ)]/1000 [V]
Of course for single phase system you have to multiply by 2 [forward and backward] and for three-phase by √3 ≈1.73.