This simple technique can yield quick paybacks while increasing the flexibility of the installation. By increasing the wire size, reduced power losses offset the cost of the wire and produce savings on energy costs. Also, the larger size does allow for increasing a circtuits rating if the need arises.
Why is this important? By upsizing wire in a new installation, the engineer or contractor can demonstrate the real savings to the customer as well as the advantages of lower generated heat and increased flexibility of the installation. In addition, when less heat is generated the result is reduced energy requirements for fans and air conditioning systems.
Of course, there are many factors that must be considered in any installation. But for most new applications, where the cost of labor and conduit for the installation outweigh the cost of wire, the increased size of the wire can pay for itself in less than two years. At the same time, increased wire size is insurance against changing future needs and assures lower voltage drops. Some companies, as a matter of course, specify wire two or three sizes larger than minimum requirements in neutrals, which are often overloaded due to harmonics.
Key elements that affect the payback, and thus the economic incentive, to install larger wire gage, are the duty cycle, load factor and electricity price. When using the same size conduit, the increased cost of wire is minimal. As the examples below demonstrate, the payback for upsizing can be quite short, even in single phase lighting circuits, or one to two shift commercial settings.
Example I2R savings and short paybacks apply to single-phase systems as well as large.
Take the case of a single-phase, 15 amp lighting load operating continuously. To simplify, assume the load is concentrated 100 ft. from the panel.
#12 AWG #10 AWG
Conduit Size 1/2 in. 1/2 in.
Estimated Loss (at 15 amp load and 40°C, and 37°C,respective conductor temps.)
77 W 48 W
Wire Cost $11.82 $18.57
Conduit Cost $42.00 $42.00
Incremental Cost $6.75
Energy Savings 254 kWh/year
Dollar Savings: at $0.07 per kWh
5 months Dollar Savings: at $0.10 per kWh
3 months Dramatic, short term paybacks in a single-phase run,
with flexibility for future load changes.
This article was edited to remove examples and justification for increasing wire size in a commercial application.
For the complete article, see the Copper Development Association website.
Ok, in a typical residential home, a circuit isn't likely to carry 15 amps all the time. But the example holds true with a longer payback period. Use of #12 wire vs #14 in a 15 amp lighting circtuit will pay for itself in a relatively short time.