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Current clamp working principle.

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zoulzubazz

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Hi,

I was trying to understand how an AC current clamp works. After some googling I understand that the current clamp loop itself is an transformer core and the AC mains cable is a transformer single turn winding. The magnetic-flux produced by the current in the mains cable is linked to the secondary winding via. the current clamp loop. Figure attached for reference.

Now all AC cables have a current return wire (live and neutral), so won't there be a return current flowing in the opposite direction? Wont the fluxes produced by the currents in opposite directions cancel each other out hence inducing no current in the current clamps winding? The picture attached shows current flowing in one direction only, is this wrong or am I crazy?


current_clamp.png
 

tsan500

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Typically in household single phase equipment AC cable indeed have a live and neutral and it is not possible to measure with current clamp on that case. On industrial installation typically individual wires are wired to contactor terminals etc. and it is possible to measure phase current. For example, it is quite easy to measure all three phase current of the (smaller size) motor to see if the phase currents are balanced or not.
 

Pjdd

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Now all AC cables have a current return wire (live and neutral), so won't there be a return current flowing in the opposite direction? Wont the fluxes produced by the currents in opposite directions cancel each other out hence inducing no current in the current clamps winding?
Your understanding of the principles is correct. What you missed is that the clamp should enclose only one side of the wiring - either the phase wire or the neutral, not both.
 

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