# Voltage Drop URD



## Bubbles (Sep 27, 2007)

Here is one. Running a 300ft run of 1/0, 1/0, #2 URD as spec'd by PUCO. Anyone know how to factor in the Resistance of 2 different sized conductors into the formula? Use the smallest? Largest? Both? Won't affect job but just curious. Is there an alternate formula out there I don't know about...

later


----------



## 480sparky (Feb 1, 2009)

I'd just punch in the resistance of the 1/0 and call it good.

If you think you need to calculate it for the neutral, you would need the amps from the load calc. Figure the voltage drop for the ungrounded one-way, then use that number to figure the neutral drop.


----------



## ampman (Apr 1, 2009)

ok whats urd


----------



## Static Design (Nov 30, 2008)

Vd= {2xL(length of wire)x R(resistance)x I(amps)}/ 1000

Whats URD? Why calculate VD for neutral?


----------



## TxElectrician (May 21, 2008)

URD = Underground Residential Distribution cable


----------



## TxElectrician (May 21, 2008)

Full Spool said:


> Vd= {2xL(length of wire)x R(resistance)x I(amps)}/ 1000
> 
> Why calculate VD for neutral?


why are you using 2xL?


----------



## 480sparky (Feb 1, 2009)

ampman said:


> ok whats urd


----------



## Static Design (Nov 30, 2008)

TxElectrician said:


> why are you using 2xL?



"2" Because there are two conductors and it's a givin variable in the standard formula. 

"L" Because chp9 t8 uses ohm/kft values, so if you don't give the distance of the run you're actually using it will throw the formula off balance and not work unless situation described was 1000ft long to throw off the the kft conversion.


----------



## TxElectrician (May 21, 2008)

Full Spool said:


> "2" Because there are two conductors and it's a givin variable in the standard formula.
> 
> "L" Because chp9 t8 uses ohm/kft values, so if you don't give the distance of the run you're actually using it will throw the formula off balance and not work unless situation described was 1000ft long to throw off the the kft conversion.


the 2nd conductor on a 120v circuit is the N. Might be why he is wanting to know how to figure vdrop w/ different size conductors.


----------



## Static Design (Nov 30, 2008)

TxElectrician said:


> the 2nd conductor on a 120v circuit is the N. Might be why he is wanting to know how to figure vdrop w/ different size conductors.



Even on a 120 circuit the wires are the same size so you still use "2". With the wires he gave I was assuming it was a 220 plus circuit or I want to know what 120 circuit requires that wire size. :laughing:

Regardless if it was a 220/110 that VD formula will work for both applications, only thing that changes is the amps and the resistance of different wire types.


----------



## Bubbles (Sep 27, 2007)

*Vd*

yes to all. 

I was using this one Vd = 2K x L x I / Cm

so since it's 1/0 out and #2 back which CM do you use? That was my dilemma. There are alot of other forums out there on this but it seems even the engineers disagree alot about VD as well. I thought this site was brutal! I think the above is just a cookie cutter formula that fits most stuff. There probably is another one out there that would fit this.


----------



## Static Design (Nov 30, 2008)

Both formulas will work, you have the same variables to answer the final product whichever method. So rather it was the one I showed you or your method both will work and give close to the same answer. Use the wire that is serving as the ungrounded conductor, not the one serving as the grounded.


----------

