I have observed my home AC line voltage at voltages anywhere from 116 to 122 VAC. Will the change in voltage affect the amount of electricity used (as recorded by the utility-supplied meter) over a given period of time? Would the type of load matter, such as a continuously running motor verses a light bulb or heating element?
I know that in actual use the load will be some combination of those two, but for simplicity’s sake assume it is one or the other exclusively.
The power company usually gurantees +/- 10 percent, or anywhere from 108 to 132 volts. Measuring 116 to 122 is pretty typical.
There have been meters made in the past which basically only measured current and assumed that the voltage was constant. Some older meters also did not work well with purely inductive loads, like all motors. I won’t guarantee you that there aren’t some of these old meters still in use somewhere, but the vast majority of them have been replaced over the years.
The newer meters measure voltage and current and can handle inductive loads without problems.
Both voltage and current affect how fast your meter turns, as should be the case.
Utilities usually use what is called an integrating watt-hour meter which measures the actual wattage used. A stator magnetic field is established by the current into your house. A rotor magnetic field is established by the line voltage at your house. The interaction of these two fields causes the rotor to turn. The average rate of turn of the rotor depends upon the product of the voltage and that part is the current that is in phase with the voltage. In addition, the rate can be set by the positioning of a magnet that establishes eddy currents in a disc attached to the rotor so that the meter can be calibrated. So if you are using 1000 watts the rotor will turn at a certain rate and if that power consumption lasts for an hour the disc will have completed a certain number of turns. This will move an indicater up to 1 kW-hr on a dial on the face of the meter.
Yea. If we assume the load doesn’t change, you’ll use about 10% more power when the voltage is 122 VAC vs. 116 VAC.
But in reality you won’t. This is because many loads (e.g. motors) are somewhat non-linear.