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I have a SCT013-030 current clamp sensor I plan to use to read out the power usage of a mains AC load. It works by wrapping around one of the AC strands of wire to measure the magnetic field.

The one I bought is calibrated so that 0-30A is 0-1V with a builtin burden resistor.

Will the output of the clamp sensor be affected by whether the inner wire is straight, or curved around the outside? By that I mean the following difference: enter image description here

Currently I have a wire loop going through the sensor like the second picture and I'm worried this brings it out of calibration. Searching online of people using these sensors shows both methods being used.

Should I worry? Or is the difference negligible compared to the sensor accuracy itself?

bergerkiller
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    It will be negligible but, why don't you prove this for yourself given that you say this: `I have a SCT013-030 current clamp sensor` – Andy aka Mar 06 '22 at 13:33
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    I don't have a stable reliable AC load I can use to verify the measured values change when wrapping or not - especially not if the difference is very small. But such differences can accumulate over time – bergerkiller Mar 06 '22 at 13:36
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    **Bent-wire** risks putting stress on the (blue) plastic clamp that ensures tight magnetic-coupling... it takes very little air-space between magnetic core halves to introduce magnetic leakage paths. The **straight-through** wire should be stress-free. Cleanliness of those mating magnetic surfaces probably has a larger error effect. – glen_geek Mar 06 '22 at 13:47
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    That's a fair point, I'll be sure to give it a little more slack to avoid slow degradation of the wire loop to prevent overstress causing a broken wire or potentially, fire. – bergerkiller Mar 06 '22 at 13:54

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If the clamp meter has an infinite permeability core, then there will be absolutely no difference in reading between the two configurations you show. The core induction will only be affected by the topology of the circuit, how many times the primary wire loops through the core.

For a finite permeability core, there will be a small difference. Usually, current clamps are made with cores which have permeability in the thousands, which correspondingly limits the errors to the order of small fractions of a percent, for this very reason.

You should ensure the mating surfaces of the magnetic core are clean before you clip the clamp round the wire. An an experiment, you could put a small airgap into the magnetic circuit by holding it closed with a sheet of paper or two in the clip-side gap (don't close the clip and possibly strain it). This wrecks the effective permeability of the magnetic circuit, and you should find the accuracy decreases, and the sensitivity to wire position increases. Only pack the clip-side gap if you want to try this experiment, don't strain the hinge by packing that side.

In the limit, a Rogowski Coil uses an air core, and has to be completely symmetrical to achieve the same independence of reading on conductor positions.

Neil_UK
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  • I can confirm that indeed, with the clamp core halves not perfectly touching, accuracy drops like a brick and turning the sensor around had a huge impact on the measured output. I'll trust the theory then that there won't be a big impact of the little loop. I'll still keep glen_geek's advice in mind to give it a slight slack from a durability standpoint. – bergerkiller Mar 06 '22 at 14:06