Current Transformer Question

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I am putting in a 200 amp service in my work shop and would like to monitor the total pull (amps) all the time as I'm running a lot of heat generating equipment. I have the 200 amp panel gage and a 200:5 current transformer and was wondering, do I run just one side of the 220v through the current transformer or both incoming 110v wires?

I was thinking that since some equipment will be running on 110v and will obviously be pulling on one leg of the 220v and some running on

220v at the same time, how do I hook up the current transformer to read everything on both legs? Does the pull even out?

Thanks in advance for some help here.

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On Sat, 8 May 2004 20:12:24 -0400, Jerry Anderson put forth the notion that...

If you only have one CT, you're going to be limited to reading the total

220 load, plus whatever portion of the 110 load is coming off of that side. If you run both sides through the same CT, they'll null each other out.
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Is it a window CT? Is is marked with a rating factor?

--s falke "Jerry Anderson" wrote... I am putting in a 200 amp service in my work shop and would like to monitor the total pull (amps) all the time as I'm running a lot of heat generating equipment. I have the 200 amp panel gage and a 200:5 current transformer and was wondering, do I run just one side of the 220v through the current transformer or both incoming 110v wires?

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If you put both through the CT but in opposite directions, that would work, but you would need a 400A CT transformer and you will have to divide the answer by 2 (which could be done by changing the meter scale), Alternatively regard the reading as the addition of currents in each leg (which is after all what it is), and effectively your 120V current draw (if you are estimating power consumption).

This would give a clue to the heating load (although a power meter would be better of course), but it would not be any use if you wanted to see the actual current in each leg, e.g. a reading of 250A (before divding by 2) could be 125A in each leg or 250A in just one leg.

I'm not sure if anything nasty might happen with a severely inbalanced current -- I think it will just induce a tiny voltage drop in the other leg equivalent to the voltage drop across the CT in the high current leg, which would be miniscule and insignificant.

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| I am putting in a 200 amp service in my work shop and would like to | monitor the total pull (amps) all the time as I'm running a lot of heat | generating equipment. I have the 200 amp panel gage and a 200:5 current | transformer and was wondering, do I run just one side of the 220v | through the current transformer or both incoming 110v wires? | | I was thinking that since some equipment will be running on 110v and | will obviously be pulling on one leg of the 220v and some running on | 220v at the same time, how do I hook up the current transformer to read | everything on both legs? Does the pull even out? | | Thanks in advance for some help here.

If you run only one side, all the current on the other side is then not measured. Also, you'd be getting the same reading for a 10 amp 120 volt load between the measured line and neutral as you would be getting for a

10 amp 240 volt load between the measured line and the unmeasured line.

If you run both lines through in the same direction, you would see only the difference. It would show the imbalance in your load plus any ground leakage, not the load itself.

If you had a 400:5 CT you could run one wire through the window in one direction, and the other wire through the window in the opposite direction to get the summation (they being opposite phases, you add them in opposite directions). But the sum of TWO 200 amp conductors is 400 amps, and that would exceed the current rating of your 200:5 CT and the 5 amp meter you attach to it.

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Not really possible with one current transformer. With both legs going through the donut in one direction the 220V load cancels and is not measured. Reverse the polarity of one leg and the 220V reading is double. Phase to Neutral loads can be measured by having one reversed polarity leg .. but the 220V is a problem. The best idea would be to get a second CT and and a shorting ammeter switch that allows switching the meter between legs.

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