1. Industry, http://en.wikipedia.org/wiki/industry.
2. Secondary Sector of the Economy, http://en.wikipedia.org/wiki/Secondary_sector_of_the_economy.
3. Opportunities for Energy Savings in Residential and Commercial Sectors with High Efficiency Electric Motors;Little,1999
4. U.S. Department of Energy, Industrial Technologies Program. http://www1.eere.energy.gov/industry/bestpractices/motors/html.
5. Variable Frequency Drives,2000