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A 24V DC power supply is supplying around 2.4A to a pure resistive load. The input voltage is 230Vrms. So I estimated the rms current drawn from the power network as:

P/230 = (24*2.4)/230 = 250mA.

And with a multimeter this current is measured as around 260mA. So it was consistent.

But when I measured with a current clampmeter(which is very new with a calibration certificate), the clampmeter shows around 430mA.

(I measure the rms value of the Line current in both multimeter and clampmeter cases)

Here is the manual of the clampmeter. And under the electrical specifications it provides the following:

enter image description here

And here is the part from the calibration certificate:

enter image description here

Given the electrical characteristics and the calibration information, is 430mA measurement for a 260mA current expected for the provided error range or something is wrong?

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  • \$\begingroup\$ Assuming the 260mA are correct (your multimeter has its tolerances too) you can just simply take all the tolerances and appply the highest and lowest cases to that value and will end up with a range that could be displayed. \$\endgroup\$ – PlasmaHH Oct 18 '18 at 8:52
  • \$\begingroup\$ Do you mean max should be around 230 + 1(.5/100)*230 ? But this is much smaller than 430mA. And I also dont know what they mean by D. In calibration certificate there is only one measurement for 60A and it says 50 would show up as 50.39. All these to me will not make it even closer to 430mA. :( \$\endgroup\$ – user1234 Oct 18 '18 at 8:56
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    \$\begingroup\$ A DC current clamp meter with a measurement range of 60 A is not useful to measure about 0.25 A precisely. You need a meter with a range of about 1 to 0.5 A. \$\endgroup\$ – Uwe Oct 18 '18 at 10:24
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    \$\begingroup\$ The specifications say they apply from 5% to 100% of full scale. On the 60A scale, 5% is 3A. So, all bets are off - you are trying to measure something at less than 0.4% of full scale. It also says that the measured AC current will be off by no more than 0.3A depending on which way the clamp is placed around the conductor. So, that's the size of your discrepancy right there. Wrong tool for the job. \$\endgroup\$ – JRE Oct 18 '18 at 10:38
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    \$\begingroup\$ The meter accuracy is +/-1.5% on either scale. On the 60A scale, that would be +/-0.9A. You're well within the accuracy limits of the meter. \$\endgroup\$ – Dave Tweed Oct 18 '18 at 12:18
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You appear to be assuming 100 % efficiency in the power supply. If it is a linearly regulated supply, it will be well short of this. Even a switchmode might be only 70~80 %. The other thing to take into account is the power factor of the supply. A normal transformer/rectifier/capacitor supply may have a power factor of 0.66, at a guess. This would mean that the product of the input rms voltage and rms current will be about 50 % higher than the real power delivered.

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