How do electric meters work?
PH has it slightly wrong, by the way. It’s not energy that’s voltage times current, but power. The unit of power is the watt. One volt times one amp is one watt. So, a sixty watt light bulb being run off a 120V supply will be drawing half an amp. A kilowatt is a thousand watts. Appliances in the kilowatt range usually have some kind of heating function: bar radiators, clothes dryers, electric kettles etc. Energy is voltage times current times time. The official SI unit for energy is the joule – one watt being consumed for one second. More commonly seen on household electricity bills is the kilowatt-hour – one thousand watts being consumed for one hour. A kilowatt-hour is 3600 joules, for what that’s worth. You will occasionally see people who speak of “kilowatts per hour”. Ignore them; they are confused. If you run a two-kilowatt heater for one hour, you’ve used two kilowatt-hours of energy. You’re charged for total energy use. It doesn’t matter to the electricity company whether you u
A kilowatt is a thousand watts. Appliances in the kilowatt range usually have some kind of heating function: bar radiators, clothes dryers, electric kettles etc. Or Pentium 4 CPUs, which pretty much have a heating function too 😛 (okay, okay, not a kW, but you could fry an egg!) You’re charged for total energy use. It doesn’t matter to the electricity company whether you use your kilowatt-hours slowly (by running one small lamp for a long time) or quickly (by running your huge air conditioner for half an hour); it’s the total number of kilowatt-hours you use in a given billing period that costs you. Further to defcom1, large organizations are also billed for peak demand, which is the peak kW load you put on the system over the billing period – so, it does matter when you use stuff to the electric company if you are really big. It is unlikely that residential customers will ever see that kind of billing exactly.
With an old-style electromechanical meter, you are indeed being charged for the energy used up by the running of that meter. But, by design, it doesn’t take very much power at all to run one of those things; the cost might be measurable in cents per century. With the newer-style electronic meters, I’m not sure whether the power supply for the meter itself comes from your side or the utility’s side; but considering that the power required is of the same order as that needed for a pocket calculator that can run for years on one tiny button-style battery, once again it really doesn’t matter.
