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NEMA - National Electrical Manufacturers Association     This is an organization that sets standards in the United States for electrical equipment including circuit breaker boxes, wiring, and electrical connectors. http://www.nema.org

Noise     Acoustical noise in dB(A) at 1 meter. Logarithmic scale. Each 3dB reduction represents 50% less noise. Issues include the pitch and speed of the fan blades, the hub size, the venturing depth, the bearing quality, and the layout of the power supply components.