Specifications

How Watts, VA, Power Factor, and Efficiency are Related
Question: How are Watts, VA, Power Factor, and Efficiency related?
Answer: "Watts" is a scalar quantity, often referred to as power, and is frequently used in conjunction with
measuring system efficiency. Watts is the energy supplied by the utility company over a given period of time to
accomplish work for the consumer. Except for heavy industrial consumers, the utility company only bills users for
the watts consumed (not VA). Watts are directly convertible into mechanical work (horsepower) or BTUs (British
Thermal Units) of heat.
1 Horsepower = 746 Watts;
1 BTU/Hr = 0.293 Watts
Mathematically, a watt is a scalar quantity resulting from the vector product of two vector quantities (volts and
amps). It is not the simple algebraic product of the rms voltage times the rms current.
"VA" on the other hand is the scalar quantity resulting from multiplying the rms magnitude of the vector quantities,
volts and amps. This resulting quantity will never be smaller than the watts demanded by an instrument. Uninformed
individuals incorrectly use VA to assess a product's over-all efficiency and power demands. Correctly applied, VA is
used to determine proper ac mains conductor gage and circuit breaker sizing as well as "power factor".
"Power factor" is, for a given set of conditions, the watts consumed by a product divided by the VA necessary to
deliver that power. The power factor will only equal 1.0 when the load is purely resistive; i.e., watts consumed
equals the VA necessary. In real life this happens infrequently. More times than not, the power factor is a number
less than 1.0.
As the load becomes more reactive, a greater number of VA is required to deliver the same number of watts to the
load. Assuming the rms mains voltage remains fixed, the decreased power factor necessitates a larger rms current be
available to supply the same nominal number of watts to the load. The power utility and distribution grid must be
capable of generating and distributing this disproportionately high level of current. This is why the utility companies
are desirous of power factors near 1.0 for products.
"Efficiency", is simply the work done by a system divided by the work supplied to the system. For an electrical load
under a given set of conditions, this is usually the output power divided by the input power. The resulting number is
always less than 1.0. The difference between the output power and the input power is the number of watts lost from
the system in the form of heat. Lost watts can be converted into BTU's/Hr and equates to the amount of heat which is
released into the ambient surroundings.