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Can I measure a 240 VAC two-wire (no neutral) U.S. residential circuit with one CT?

April 26, 2017circuit CT measure Neutral Residential two-wire VAC

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Can I measure a 240 VAC two-wire (no neutral) U.S. residential circuit with one CT?

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WattNode® meters reference their measurements to neutral or earth ground if there is no neutral. So we recommend monitoring both lines and using two CTs for best accuracy. However, if there is no neutral (or no neutral current), then the current is identical in both wires. The voltage (relative to ground or neutral) will be nearly (but not exactly) identical for both phases. So by using one CT, you will measure one-half of the load. You can double the results (or double the effective CT rated amps) to correct for this.