Power rating

In electrical engineering, mechanical engineering and other disciplines, the power rating of equipment is defined as the highest power input allowed to flow through particular equipment. According to the particular discipline, the term "power" may refer to the electrical or mechanical power. A power rating can also involve average and maximum power, which may vary depending on the kind of equipment and its application.

Power rating limits are usually set as a guideline by the manufacturers, protecting the equipment and simplifying the design of larger systems, by providing a level of operation under which the equipment will not be damaged while allowing for a certain safety margin.

In equipment which primarily dissipate electric power or convert it into mechanical power, such as resistors, and speakers, the power rating given is usually the maximum power that can be safely dissipated by the equipment. The usual reason for this limit is heat, although in certain electromechanical devices, particularly speakers, it is to prevent mechanical damage. When heat is the limiting factor, the power rating is easily calculated. First, the amount of heat that can be safely dissipated by the device, ${\displaystyle P_{D,max}}$, must be calculated. This is related to the maximum safe operating temperature, the ambient temperature or temperature range in which the device will be operated, and the method of cooling. If ${\displaystyle T_{D,max}}$ is the maximum safe operating temperature of the device, ${\displaystyle T_{A}}$ is the ambient temperature, and ${\displaystyle \theta _{DA}}$ is the total thermal resistance between the device and ambient, then the maximum heat dissipation is given by

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