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Measuring Power Consumption on 220V circuits


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#1 SteveQ

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Posted 16 March 2009 - 11:44 AM

Perhaps this is a dumb question, but I need some input on the proper use of a current sensor on a 220-240V circuit.

To get an estimate of power consumption, is it necessary to measure the current flow on both legs of a 220V circuit?

Steve Q

#2 DavidL

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Posted 16 March 2009 - 12:13 PM

Perhaps this is a dumb question, but I need some input on the proper use of a current sensor on a 220-240V circuit.

To get an estimate of power consumption, is it necessary to measure the current flow on both legs of a 220V circuit?

Steve Q


If you are interested in getting total power usage, then yes, you would need to measure both legs to get the total 110 volt usage.

#3 SteveQ

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Posted 16 March 2009 - 12:43 PM

David,

Thanks for the response. Actually, I am trying to do just the opposite. I don't want the total power consumption (I can get that via the power company). I am thinking about monitoring just one leg of the 240V feed and then try to make some sense of the data. It should be possible to map the various circuit breakers to either side A or side B of the 240V feed. This is fine for the 120V stuff but it gets complicated by the 240V stuff. I am wondering it there is some way to subtract the 240V contribution.

Steve Q

#4 Sokoloff

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Posted 16 March 2009 - 01:12 PM

If you have a pure 220 load, then there's no need to measure both legs, as they are by definition the same current.

If you have a mixed 220/110 load (a load wired with 4 conductors, black, black, white and ground) such as an oven [220 for heating, 110 for controls and displays], then the currents on each of the black wires could be different (by the amount of the current consumed at 110V)

What is it that you're trying to do exactly? (in "real world" language, not in electrical panel/circuit language)

#5 SteveQ

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Posted 16 March 2009 - 03:41 PM

What is it that you're trying to do exactly? (in "real world" language, not in electrical panel/circuit language)


I'm trying to get a better handle on where any "phantom" loads might be hiding. I have a kill-a-watt an I have identified how much individual devices consume, but if I add them all up its nowhere close to my power company bill. So I thought I would put at current sensor on the supply line, turn off all the breakers, then turn them on one at a time to see how much each circuit draws under "normal" circumstances. That would give me a baseline. Then I plan to see how the power draw changes throughout the day/week. Its not rocket science, I just wondered what the impact of the 220V appliances would be. I suppose I could turn off all the 220 breakers! Then I would know the power being consumed was due to lights, TV, small appliances, etc.

In order to be greener, I think we have to know where the energy is going.

Steve Q

Edited by SteveQ, 16 March 2009 - 03:47 PM.


#6 Spintop1

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Posted 28 March 2009 - 09:37 AM

What is it that you're trying to do exactly? (in "real world" language, not in electrical panel/circuit language)


I'm trying to get a better handle on where any "phantom" loads might be hiding. I have a kill-a-watt an I have identified how much individual devices consume, but if I add them all up its nowhere close to my power company bill. So I thought I would put at current sensor on the supply line, turn off all the breakers, then turn them on one at a time to see how much each circuit draws under "normal" circumstances. That would give me a baseline. Then I plan to see how the power draw changes throughout the day/week. Its not rocket science, I just wondered what the impact of the 220V appliances would be. I suppose I could turn off all the 220 breakers! Then I would know the power being consumed was due to lights, TV, small appliances, etc.

In order to be greener, I think we have to know where the energy is going.

Steve Q

I did it using a clamp on meter. I turned off all ccts on the board, clipped the meter in place and started closing ccts, worked fine. If you want both simultaneously, get a clamp on for both sides.
my2cents

#7 Spintop1

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Posted 28 March 2009 - 09:39 AM

What is it that you're trying to do exactly? (in "real world" language, not in electrical panel/circuit language)


I'm trying to get a better handle on where any "phantom" loads might be hiding. I have a kill-a-watt an I have identified how much individual devices consume, but if I add them all up its nowhere close to my power company bill. So I thought I would put at current sensor on the supply line, turn off all the breakers, then turn them on one at a time to see how much each circuit draws under "normal" circumstances. That would give me a baseline. Then I plan to see how the power draw changes throughout the day/week. Its not rocket science, I just wondered what the impact of the 220V appliances would be. I suppose I could turn off all the 220 breakers! Then I would know the power being consumed was due to lights, TV, small appliances, etc.

In order to be greener, I think we have to know where the energy is going.

Steve Q

I did it using a clamp on meter. I turned off all ccts on the board, clipped the meter in place and started closing ccts, worked fine. If you want both simultaneously, get a clamp on for both sides.
my2cents



#8 SteveQ

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Posted 02 April 2009 - 11:59 AM

Spintop, Thanks for the suggestion. I have also used a clamp-on meter. But some loads are not on all the time. I think that some wall warts draw much more power depending on the state of charge of the battery they are charging. So I would prefer to monitor the circuit for a few days/weeks. Below is a graph showing the output of the the current sensor on one leg of the supply line. I have tracked down most of the spikes but there are still a few I can't identify.

Steve Q

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