ECN Forum Forums General Topics of the Trade General Discussion Area Voltage drop??

Ever try Martindale's Calculator site? It is amazing. Here's a link to the electrical ones: http://www.martindalecenter.com/Calculators4A.html

electure,
He asked for the formula, he got the calculators.
Whats your beef. I read all the posts.

If you require lenghthy responses on this forum just let me know.

"He asked for the formula, he got the calculators."

The sentence should be self explanatory. Some members are here to learn, (my aged self included). In depth education is sound education. Unlike calculators, it explains the hows and whys.

As a matter of fact, until Greg was kind enough to post his calculator, SparkyNC got 1. (The other one wouldn't open on SparkyNC's computer.)



"I" don't require anything.
A moderator is just a member who's been around the site and carefully read/responded to a lot of threads, nothing more.

It may be to your advantage to check into using a buck-boost transformer to reduce your wire size at the far end.

Wow, all that talk and still no formula?

VD = (2LIK)/CM

Or in English:

VD – Voltage Drop
L- Lengths
I- Amps
K- Constant for Copper (use 12.9 for CU and 21 for AL)
CM- Circular Mills (page 635 Table 8 of the NEC-2005)

Or you can back into it by:
CM = (2LIK)/ VD

So if 5% of 240 = 12v then…

(2 x 250f x 50A x 12.9)/12v = 26,875 cm

Go to page 635 Table 8 of the NEC-2005: Looks like # 6 is (26,240) so the next size up is #4 (41,740)

The formula is in the link I gave, but not the answer

Time to type.....
Voltage drop is a FPN in the NEC, 2% feeders, 3% branch for a total of 5%. But, it's a FPN, not 'Code'.

That said...thanks to Ito for doing that typing.

Kale:
The buck/boost solution is only recomended (IMHO) with a constant load. If you size the B/B for a 50 amp load, and it drops to 10 amps, you can/may get an overvoltage situation at the 'load'.

Sounds similar to my class Wed PM

If I was going to go with a transformer, I would go with 2. Step that up to 480 and back down to 120/240 but at that point bigger wire would probably be cheaper. Trying to boost the drop up at the far end is just paying extra to hide the waste heat you are losing along the way.
#1 al would get you in under 3% and probably not break the bank. #2al gets you up to 3.3% but that assumes 50a load and that would have to be a peak. I bet 40a would be a better working number. If you do that you can get in around 2.5% with #4 copper or the #2al.