A larger conductor means less voltage drop and higher efficiency.
Don’t be one of those people who saves money by sizing conductors only as large as you have to (by Code), but then turns around and recommends a big investment in a new lighting system to save energy. OK, so you’re not that kind of person. But does your company “save money” by scrimping on power distribution conductors and then spend big bucks on a lighting technology change?
Sure, upgrading to a more energy-efficient lighting technology is almost always a good idea. But that is also true of running your circuit with 12 AWG conductors when the Code minimum is 14 AWG. The reason is the larger conductor means less voltage drop and, therefore, higher efficiency of operation.
The NEC does not require you to account for voltage drop (for reasons stated in 90.1), except for sensitive electronic equipment [647.4(D)]. The NEC does have an Informational Note following 210.19(A), where a 3% limit in voltage drop for branch circuits is discussed. It’s discussed, but it’s not presented as a requirement.
If you calculate the voltage drop and see it’s 2.9%, that means you’ve got a “reasonably efficient” circuit. But what if, for a small extra expenditure (upsizing the current-carrying conductors one size), you could lower the drop to 1.6%? Your circuit would be much more efficient.
How far do you take this upsizing? Of course, you don’t want to be running 4 AWG for your 120V, 20A circuits even though that would be very efficient with only a teeny amount of voltage drop. But try finding a 120V, 20A receptacle with terminals that accept this size wire.
But those terminals will accept 14 AWG or 12 AWG. The cost difference in conductors is minimal. Unless you’re running many circuits in raceway and are concerned about the raceway size, this is a small additional materials cost. And it will provide significant savings over the life of the installation. Especially when repeated in all branch circuits.
Minimizing voltage drop as far as is practical is only one of the many ways that you can make electrical infrastructure more energy-efficient. And it’s perhaps the least expensive way available.
Yet, sometimes it’s not enough. Let’s say you run the voltage drop calculations, and the only way to get even that 3% is to run a conductor that you know is too large for the terminals on the breakers (or the utilization equipment).
An electrical engineer at a Tennessee industrial services firm solved this problem with 120V branch circuits at one client’s facility by adding a transformer and panel near one “load cluster” and, as he said, “letting the 480V power distribution do the long-distance dialing.” Yes, that was in the days when we paid for long-distance calls. But the idea does have a certain, er, ring to it.