[RE-wrenches] voltag drop

[David Brearley]

Marco,

The formulas I learned in school are:

Single-Phase Vd = (2 * d * k * I) / cm

where: d = distance; the constant k = 12.9 Ohms for Cu & 21.2 Ohms for AL; I
= current; cm = circular mils

3-Phase Vd = (1.73 * d * k * I) / cm

My note are failing me, but I believe d is actually the one-way distance.
This is multiplied by 2, in the single-phase calculation, to account for the
round trip distance. In the 3-phase calculation 1.73 is used instead. Table
8 in the NEC has the conductor properties. This is where I always look up
circular mils.

In the past I¹ve run these calculations against my ElectriCalc & had things
check out. 


> 
> I feel kinda foolish in asking this.....but when calculating voltage drop in a
> conductor over distance, do I use the one-way or round-trip distance?  thanks,
> marco  Marco Mangelsdorf, Ph.D., President
> Electrical Contractor License C-26351
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> 
> 
> David Brearley, Technical Editor
> SolarPro magazine
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