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I have a single phase 208v circuit that I want to measure the amps on. What is the proper way to measure the amps?

This is for a connection with 2 hots and a ground wire, no neutral coming from a 120/208 wye transformer.

Do I put the CT on one leg and measure that?

Do I put a CT on both hot legs and average it?

Or do I put the CT over both "hot" wires?

Or something else...

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If you are sure there is not a ground fault (i. e. current flowing through the ground wire), then all current flowing through one leg must also flow through the other. Therefore, it is sufficient to measure only one leg.

If you are not sure about ground current and don't have a GFCI on the circuit, you would need an additional current transformer, either on the ground wire or the other leg.

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  • \$\begingroup\$ If the CT is a current clamp type instrument you can check the ground current ... I believe it should be less than 3.5mA ... although this sounds like an industrial application so it could be higher ... \$\endgroup\$ – Spoon Aug 20 '14 at 10:54

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