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In my camper I have standard 3 wire power coming in. 2 are 120vac and 1 neutral. Since the wires feed separate sides of the circuit breaker box with the neutral being common to both.

Can I place 1 current monitor coil around the neutral wire and get the total current used in both 120vac lines since it is the common "return" for both 120vac feeds to my circuit breaker box.

My desire is to get total power consumption using only 1 coil. As most 220V appliances simply split power and supply 2 - 120vac lines in the dryer to balance the load. i.e. a dryer separates the power... 1 side supplies 120vac to the motor, the other 120vac to the heating element.

Since both sides of the circuit breaker box share the common neutral wouldn't the current monitor show the total amperage of both sides of the box using 1 current coil?

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2 Answers 2

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Nope. The 2 lives+neutral sends power on the lives in opposite phases so there is 240V across them.

If the loads on each branch are matched then there will be very little current on the neutral. Also the dryer in your example would put the heater across the lives and the motor from one leg to neutral.

So you will need to find a 2 phase current monitor to find the actual power consumption.

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  • \$\begingroup\$ In other words, the neutral carries the difference of the currents of the live wires, not their sum. \$\endgroup\$
    – Dave Tweed
    Apr 27, 2018 at 13:24
  • \$\begingroup\$ You can however combine two current wires into one current transformer and thus one signal that is the sum. google.com/… \$\endgroup\$ Apr 27, 2018 at 14:23
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enter image description here Perhaps the lowest cost solution from a component count perspective.

It is important to ensure that the current from both phases will “add” in the current transformer.

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