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.