Installing wire only one size larger than has been required by the National Electrical Code increases energy efficiency with dramatic paybacks. 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.
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.
How important is this to the owner?
Jim Clarkson, former Corporate Energy Manager of Southwire Company, which has nearly 50 acres of industrial facilities under roof in nine states, requires that all loads under 100 A shall use wire one size larger than that required by code. "Quick payback is assured under these circumstances," says Clarkson. "Larger size applications are evaluated on a case by case basis."
A simple way to understand the dramatic impact of wire size on energy efficiency and costs is to examine the number in these examples, in which one wire size above code minimum is installed. All three examples include a separate full-size grounding conductor, following current recommended practice, and use THHN copper conductors.
|3/0 wire||4/0 wire|
|Conduit Size||2 in.||2 in.|
|Estimated Loss (at 75% load and 44°C and 40°C,respective conductor temps.)||708 W||554 W|
|Energy Savings: at 75% load||1,237 kWh/year|
|Dollar Savings: at $0.07 per kWh Payback||$86.59/year 2 years, 9 months|
|Dollar Savings: at $0.10 per kWh Payback||$123.70/year 1 year, 11 months|
|In this example, the payback is under 3 years, and the savings continue indefinitely into the future.|
|#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|
|Energy Savings||254 kWh/year|
|Dollar Savings: at $0.07 per kWh Payback||$17.78/year 5 months|
|Dollar Savings: at $0.10 per kWh Payback||$25.40/year 3 months|
|Dramatic, short term paybacks in a single-phase run, with flexibility for future load changes.|
|#8 AWG||#6 AWG|
|Conduit Size||3/4 in.||1 in.|
|Estimated Loss (at 100% load and 60°C and 45°C, respective conductor temps.)||711 W||426 W|
|Energy Savings||1,140 kWh/year|
|Dollar Savings: at $0.07 per kWh Payback||$79.80/year
1 year 5 months
|Dollar Savings: at $0.10 per kWh Payback||$114.00/year 1 year|
|Notice how much cooler the #6 wire operates. And less than one and a half year payback at only 4000 hours operation.|