I have an old barn to which i'd like to provide electricity.
The problem is that the barn is about 300 feet away. I understand that voltage drop over 300 feet is fairly significant. Buying thicker wire to accomodate voltage drop of that magnitude may be very costly, and I'd have to figure out how to terminate the end in the panel at such a thick gauge.
Is using a transformer at both ends a viable/smart solution?
Would using two conductors in parallel be a better or safer option?
How is something like this done normally?
Best Answer
Using Table 8 in chapter 9 of the NEC along with Ohm's Law (the max drop generally permitted by good practice on a branch circuit is 5% or 6V on a 120V circuit) gets you a minimum wire size of 6AWG in copper or 4AWG in aluminum.
Considering that 6/2 UF is $3.00 a foot at the blue borg and 14/3 UF is $0.87 a foot at the blue borg, the transformer idea looks like a good option, until you realize how much 3.6kVA of transformer will cost you -- almost $600 via McMaster-Carr, which is the cheapest supplier I could find, with an alternative part available for about $650 via Platt Electric Supply.
Even with 240V being tapped at the house (source) end of this instead of 120V (so you only need one transformer) -- you'd still be out a good $850, which is comparable to simply burying 6/2 UF. A further drawback created by the transformer idea is the extra labor involved with creating a separately derived system in the barn (the equipment grounding arrangement gets...funky, see NEC 250.30 for details), so simply burying 6/2 UF is going to be your best option.
As to terminating it in the panel? Don't worry about it! The main lugs on a panelboard will easily accept 6AWG! If you're not using a panelboard (as this is a single branch circuit feeding an outbuilding), simply use appropriate wirenuts to pigtail the 6AWG UF to a length of 10AWG for the indoor branch circuit in the barn.