Power Rating of Appliances

To understand the power rating of different appliances we need to understand the basic terminologies and concepts involved. The generic meaning of the word power means some kind of energy or strength to do a certain act. In the context of physics, power can be more narrowly or specifically defined as the measure of transformation of energy from say electrical form to mechanical form. An example can be of a fan which uses electrical energy (current) and converts it into mechanical energy (fast moving air). The power consumed by fans is generally in the range of 40W-60W.

Each appliance will require a specific amount of power to do the defined task. A monitor may consume 300W whereas a water heater may consume power as high as 2KW. This amount of needed energy is called the rating of the appliance. This power rating is decided by the manufacturer keeping in view the safety requirements as well. If the power supplied to the appliance exceeds the power rating of the appliance there is a possibility of the appliance getting damaged! In order to avoid this there is always a margin of safety maintained to protect the appliance from damage. That is, if the rating of the appliance is 75W it means the actual rating of the appliance may be in the range of 80W-85W. Else, if the power supplied exceeds the rating the appliance will be damaged. The economic implication of such damage can be huge especially in the case of electronic appliances.

Determining the power rating of appliances depends on different factors like Resistance, Load Connected and Type of Circuit. Resistance impedes the movement of electricity and hence consumes more power. This can be put in the form P=I^2 * R where I is the current, P is the power and R is the resistance. R is directly proportional to P and hence if R increases the power needed also increases. Power can vary, depending on load, especially in appliances like motors where the power consumption is higher when the motor starts. In parallel circuits, each branch consumes different amounts of power.