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a lamp, toaster, electric motor, etc.) has a rated "size" in watts. Either higher levels of power (for a given period) or longer periods of run time (at a given power level) require more energy.Īn electrical load (e.g. To produce power over any given period of time requires energy. Physical power can be defined as work per unit time, measured in units of joules per second or watts. The terms power and energy are frequently confused.
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One guide published by NIST specifically recommends avoiding "kWh" "to avoid possible confusion". However, at least one major usage guide and the IEEE/ASTM standard allow "kWh" (but do not mention other multiples of the watt-hour). This is supported by a voluntary standard issued jointly by an international ( IEEE) and national ( ASTM) organization. ), since otherwise some prefixes could be misinterpreted as a unit symbol" (i.e., kW h or kW.The international standard for SI states that in forming a compound unit symbol, "Multiplication must be indicated by a space or a half-high (centered) dot ( It is consistent with SI standards (but note that the kilowatt-hour is a non-SI unit). Other abbreviations and symbols may be encountered: The abbreviation " kWh" is most commonly used in commercial, educational, scientific and media publications, and is the usual practice in electrical power engineering. Symbol and abbreviation for kilowatt-hour Industrial users may also have extra charges according to their peak usage and the power factor.
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The unit price of electricity may depend upon the rate of consumption and the time of day. Electrical energy is sold in kilowatt-hours cost of running equipment is the product of power in kilowatts multiplied by running time in hours and price per kilowatt-hour. A 40-watt light bulb operating for 25 hours uses one kilowatt-hour. The hour is a unit of time "outside the SI", so the kilowatt-hour is a non-SI unit of energy.Ī heater rated at 1000 watts (1 kilowatt), operating for one hour uses one kilowatt-hour (equivalent to 3.6 megajoules) of energy. Note that the International Standard SI unit of energy is the joule. One kilowatt-hour is 3.6 megajoules, which is the amount of energy converted if work is done at an average rate of one thousand watts for one hour. The kilowatt-hour (symbolized kWh) is a unit of energy equivalent to one kilowatt (1 kW) of power expended for one hour. 6 Confusion of kilowatt-hours (energy) and kilowatts (power).5 Watt-hour multiples and billing units.3 Symbol and abbreviation for kilowatt-hour.