Voltage Drop Formula's
Hi all, my question is this. The 2 Formula's for voltage drop. are the 2 for single phase circuits unmerchantable? Or do the both have a specific purpose? Teaching it in my class and just wanted to give the correct answer.
Bill, I am sorry as I am not sure what you mean by "unmerchantable". We have a number of VD formulas to find various values depending on the given information. So, I recommend you post the formulas so viewers don't have to speculate on the formulas you are referring to.
Here are the 2 formula's I am talking about,
Single phase VD= 2xLxKxI/Cmil VD=2xLxRxI/1000' Is there a way to know which formula to use in a problem?
Here is the problem The Voltage Drop for a 208V single circuit with a load of 26.5 Amps using #8 stranded Copper Conductors at a length of 145'?
Which formula best fits this problem?
Both formulas are equivalent — they just start with different known values:
If you have CM area and the constant K, use the first.
If you have resistance/1000 ft handy (from Table 8), use the second.
Most electricians and exam problems prefer the resistance formula since NEC already gives ohms/1000 ft in Chapter 9, Table 8.
2 x 145 x .778 x 26.5 / 1000
5979.93/1000 = 5.98V
3% of 208 is 6.24V so obviously 5.98V is within the acceptable 3%.
Thank you that is a big help. Thank you.