Dave6
Member
- Location
- Deployed...FL when I'm not
All,
I e-mailed the engineer at copper.org. Here is his response;
I wonder where you saw that comment, because #10 wire for a 15 amp lighting load seems excessive, and boxes and other devices may change, affecting the installed cost. Perhaps a mis-print by a magazine? (Sometimes a story that I have not seen or reviewed, even though attributed to me, is published by a zealous editor.) A case may be made more easily for #12 instead of #14, but the procedure is the same for #10.
The basic wire loss calculation, simplified, is just the value of I squared R versus the additional cost of the wire.
For #14, R = 2.52 ohms per 1000 feet at 20 C.
For #12, R = 1.59 ohms per 1000 feet at 20 C (For comparison, #10 = 0.9988 ohms)
For a circuit of say 100 feet length, wire length is 200 feet ( 0.2 K ft.)
Let's assume a current requirement of 12 Amps (Limit for #14 continuous).
#14: Power = 12 X 12 x 2.52 X .2 = 72.6 WATTS x 4000 h/y = 290,304 Wh = 290.3 kWh/Y X $0.075 = $21.77 per year
For #12: Power = 12 X 12 X 1.59 X .2 = 45.79 W X 4000H/Y = 183,168 Wh = 183.1 kWh/Y X $0.075 = $13.74 per year.
Savings is $8.03 per year.
In actuality, the #14 will run hotter than the #12, so will have a bit more resistance, but temperature is omitted here.
For 15 amps load, the calculation for #12 AWG is 15 X 15 X 1.59 X .2 X 4 X $0.075 = $21.46 per year
For #10 AWG it's 15 X 15 X 0.9988 X .2 X 4 X $0.075 = $13.48 per year
The savings of $7.98 per year is then compared to the differential cost of 200 feet of the wire to get years to payback. As I said above, though, #10 requires special receptacles and boxes, which may make it more difficult to justify.
I wonder how old the source of that article is, since I have not performed this comparison for several years. Back then, larger gage was easier to justify. But prices have changed, and you should plug in current values for the wire cost, labor, and electricity price. In high energy-cost areas, like New England, upsizing is easy to justify. In areas like the Northwest, paybacks can be lengthy.
I hope this information is of help, and welcome your questions or comments.
I may bump up my HVAC unit, maybe a couple others, but that would be it.
I e-mailed the engineer at copper.org. Here is his response;
I wonder where you saw that comment, because #10 wire for a 15 amp lighting load seems excessive, and boxes and other devices may change, affecting the installed cost. Perhaps a mis-print by a magazine? (Sometimes a story that I have not seen or reviewed, even though attributed to me, is published by a zealous editor.) A case may be made more easily for #12 instead of #14, but the procedure is the same for #10.
The basic wire loss calculation, simplified, is just the value of I squared R versus the additional cost of the wire.
For #14, R = 2.52 ohms per 1000 feet at 20 C.
For #12, R = 1.59 ohms per 1000 feet at 20 C (For comparison, #10 = 0.9988 ohms)
For a circuit of say 100 feet length, wire length is 200 feet ( 0.2 K ft.)
Let's assume a current requirement of 12 Amps (Limit for #14 continuous).
#14: Power = 12 X 12 x 2.52 X .2 = 72.6 WATTS x 4000 h/y = 290,304 Wh = 290.3 kWh/Y X $0.075 = $21.77 per year
For #12: Power = 12 X 12 X 1.59 X .2 = 45.79 W X 4000H/Y = 183,168 Wh = 183.1 kWh/Y X $0.075 = $13.74 per year.
Savings is $8.03 per year.
In actuality, the #14 will run hotter than the #12, so will have a bit more resistance, but temperature is omitted here.
For 15 amps load, the calculation for #12 AWG is 15 X 15 X 1.59 X .2 X 4 X $0.075 = $21.46 per year
For #10 AWG it's 15 X 15 X 0.9988 X .2 X 4 X $0.075 = $13.48 per year
The savings of $7.98 per year is then compared to the differential cost of 200 feet of the wire to get years to payback. As I said above, though, #10 requires special receptacles and boxes, which may make it more difficult to justify.
I wonder how old the source of that article is, since I have not performed this comparison for several years. Back then, larger gage was easier to justify. But prices have changed, and you should plug in current values for the wire cost, labor, and electricity price. In high energy-cost areas, like New England, upsizing is easy to justify. In areas like the Northwest, paybacks can be lengthy.
I hope this information is of help, and welcome your questions or comments.
I may bump up my HVAC unit, maybe a couple others, but that would be it.
