Voltage drop in household wiring is costing you money

I should start this article off by mentioning that I am not an electrician, or a licensed contractor of any kind. Just your average DIYer, the kind that takes on household projects not only to save a few bucks, but because it’s interesting and enjoyable work. Recently, we did added a kitchen addition to our home. My motto has always been to choose your battles, meaning take on the projects that you’ll actually enjoy and can save money. Don’t tackle a DIY project if it will only meet one of those goals. In that spirit, we had contractors dig the basement, lay the block and build the structure.

After that, we decided we would try to tackle many of the “inside” jobs, including plumbing and electrical. In both cases, I picked up books to learn as much as I could about the building codes before starting work. The plumbing codes, to me, made complete sense and I actually found the entire rough plumbing process relatively straightforward. The electrical took me a good deal longer to prepare for. I read two books on the subject. One focused on the subpanel installation, while the other, Wiring Simplified, was a general introduction to the National Electric Code (NEC).

One of the first things that the authors of Wiring Simplified try to convey is that the NEC is not focused on efficient use of electricity, but solely on safety. Things like the number of outlets that need to be present on a given length of wall and the minimum requirement of 20 Amps for kitchen counter top circuits. These are examples of codes that represent the safety aspect of electrical wiring. The area that captured my attention the most was the wire sizing.

There is essentially a table of wire size (AWG or American Wire Gauge) requirements based on the amount of current (amps) that will flow through the wire. Again, the NEC emphasizes safety only, so their sizing requirements are determined by the minimum wire size required to safely pass a given amount of current through it. Emphasis on minimum size.

Voltage Drop

So what’s all the fuss? Smaller wires are cheaper and easier to bend and wrap around a screw. An electrician wiring your home will go with the cheapest possible wire that is approved for the load, according to the NEC. This will, of course, translate to a cheaper total cost of installation for you. But what about the continued electricity cost? Wires lose voltage as their distance increases, and the smaller the wire, the more voltage is lost.

Perhaps an easier way to explain this is by example. If you are running 10 AMP power tool on a 14 AWG circuit, where the circuit is created by a 50 ft. wire back to your circuit panel. The amount of voltage lost 2.53 volts.

If you were using the exact same setup, but with a 12 AWG wire, your voltage drop is 1.59 volts. It doesn’t seem too bad right, a difference of only about one volt is lost. But let’s see if we can convert that to a monetary figure.

Amps x Volts = Watts
10 Amps (our power tool) x 1 Volt (voltage drop diff.) = 10 Watts = .01 KiloWatts

At 15 cents per KiloWatt/Hour
$.15 * .01kW = $.0015 = .15 cents per hour of use

Ok, big deal, it’ll cost me an extra 1/10th of a cent for each hour I use my power tool on a 14 AWG wire vs. a 12 AWG wire.

But, we really like our tool and use it for an hour every day.

.15 * 365 days/year = 54.75 cents per year

Again, that figure really won’t turn any heads. 55 cents per year extra cost is going to motivate anyone to consider a higher installation cost.

But, I’ve read that the average household energy consumption is between 7 and 10 amps continuous. That means, every hour, between 7 and 10 amps is used in your home. This fits somewhat nicely into our formula above, since we used a 10 amp power tool for our example math.

.15 * 24 hours * 365 days/year = $13/year