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Electric Power & Utilities/240V VS 120V Power Consupmtion


QUESTION: Hello, I was told that cost wise a 500W at 240v appliance will cost same as 1000w 120v on my electricity bill and I not certain about it...

Can you please clarify: If I run 2 appliances for One Hour. One is rated 500W at 120v and the other 500W at 240V  - What will be the cost on my electricity bill? Is the first (120v) going to cost me half than the other (240v) or same?

Thank you,

ANSWER: Hi Tim -
Your electric bill charges you for  watt-hours of energy consumed. It doesn't matter if you consumed the energy at 120v or at 240v, either way your meter would say you used the same amount of energy and you'd be charged the same.

Energy (watt-hours) = current (amps) x volts x hours
At higher voltage you draw less amperage for the same energy.

Good luck!

---------- FOLLOW-UP ----------

QUESTION: Thank you for prompt reply Bill, Just to be clear, a 500W / 240v appliance will cost same to run as 1000W / 120v appliance and will cost "twice" as much on my electric bill to run than appliance 500W / 120v, correct?

Is your home voltage 120v or 240v or are both available? What voltage are you plugging each appliance into?
I assumed you were plugging 120 into 120 and 240 into 240v.

---------- FOLLOW-UP ----------

QUESTION: Thanks Bill, The house is 120V in Canada, main power in is 400 AMP 240V on 2 pairs. While light fixtures and everything else in standard 120V, there are lots of appliances 240V in many rooms, not only the kitchen or for the dryer. SO I have 240V and 120V available everywhere.

I was trying to figure out how much those appliances cost to run. For example, I have a heater in the garage connected to 240V (same way as you hook a 240v dryer in US/Canada) and its 6000 Watts. I need to run it ON for one hour to heat the garage. If 1 AMP/hr cost $0.13 (thirteen cents) how much it cost to run...?

So, Tim your garage heater is designed to produce 6000 watts of heat when plugged into a 240 volt socket.
If you run it for an hour it will use about 6000 watt-hours of electrical energy. That would be 6 kilo-watthours, or 6 kWh for short.
If your electric bill says you are being charged $0.13 for each kWh, then it cost you 6 x 0.13 = $0.78 for that heat.

If you had a different heater designed to produce 6000 watts on 120 volts, it would also would cost you $0.78 per hour.

If you could somehow take the first 240 volt heater and plug it into a 120 volt socket, it would produce much less than 6000 watts of heat and use much less than 6000 watts of electricity that would cost much less than $0.78 per hour.

if you could somehow take the second 120 volt heater and plug it into a 240 volt socket it would probably burn out instantly, producing only a short flash of heat, but costing you the price of a new heater!

Hope this is a bit clearer.
Good luck!

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W.A. (Bill) Stevens


I can explain the technical and economic tradeoffs of making electricity from natural gas, coal, nuclear, wind, solar, and biomass energy sources. I'm familiar with air pollution control technologies, including CO2 capture and sequestration. I have a good understanding of the science on global warming and can explain how energy use inefficiencies and various fuels and technologies contribute to that process. I can tell you why we have to build more new gas, nuclear, wind, and solar power plants, but will still have to keep using coal for a few decades to make elctricity. I can explain energy conversion efficiency and power plant operations. However ... I'm not an electrician, so probably cannot help with questions on motors or wiring. ;-)


Forty years as a registered professional mechanical engineer.

Graduate of Purdue University, School of Mechanical Engineering.

Past/Present Clients
EPA, DOE, State Department, USAID, World Bank, Bechtel Power Corporation, U.S. Generating Company, numerous electric utility and independent power companies.

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