Perplexing amp reading from different multimeters

[JackCW]

Hello everyone, I'm new to the forum. Thank you for allowing me to join. I am a DIY'er, I've been doing much of my own wiring for years, but I know my limits.

I have three digital multimeters: a Klein CL-800, a Southwire 21550T (both clamp-style), and a Fluke T5-600, which is an open-end tester. I had an issue in my Morton building, so I tested the amperage on one leg of the subpanel. Using the Klein and Southwire, they read 7.5 amps, but using the Fluke, it read 4.2 amps. That's quite a spread. Does anyone have any idea why there would be such a large discrepancy in the reading? I changed the batteries in the Fluke, same results. When measuring voltage all three are the same.

Thanks,
Jack

 

[Megawatt]

Hello everyone, I'm new to the forum. Thank you for allowing me to join. I am a DIY'er, I've been doing much of my own wiring for years, but I know my limits.

I have three digital multimeters: a Klein CL-800, a Southwire 21550T (both clamp-style), and a Fluke T5-600, which is an open-end tester. I had an issue in my Morton building, so I tested the amperage on one leg of the subpanel. Using the Klein and Southwire, they read 7.5 amps, but using the Fluke, it read 4.2 amps. That's quite a spread. Does anyone have any idea why there would be such a large discrepancy in the reading? I changed the batteries in the Fluke, same results. When measuring voltage all three are the same.

Thanks,
Jack

I really wouldn’t worry about 3 amps by using 3 different meters or amp probes. I’m sure that all meters do not read the same. Maybe that 1 meter is cheaper than the others. Hope this helps

 

[brianmoooore]

Are they measuring a nice clean sine wave, or are there electronics distorting it?
Set up a known resistive load, calculate the current by Ohm's law, and see how that compares.

 

[Avo Mk8]

I just had a look, and the Klein and the Southwire are both "True RMS" meters, whereas it appears the Fluke is not, as it says "averaging" against ac response in the spec.
So if the load being measured has a power factor other than unity, or the load (or part of it) is controlling its power by chopping the mains sine wave, you might expect the Fluke to show a different reading, but that is quite a difference.