EKM-251DS reading low

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Joined: Tue May 14, 2019 5:20 am

EKM-251DS reading low

Post by bonete1 » Tue May 14, 2019 12:19 pm

I did install an ekm-251ds for an air conditioner 240V. Also installed in the same hot lines my old OWL meter to compare readings. I found that the ekm read 18% less or lower than the OWL. Any reason for this?

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Joined: Fri Nov 04, 2011 7:42 pm
Location: Santa Cruz, CA

Re: EKM-251DS reading low

Post by Jameson » Fri May 17, 2019 9:46 am

Hello Bonete1,

The OWL is an energy monitoring device. It is closer to an amp meter than an actual kWh meter (it only has CT connections). It is not very accurate, it does not measure the voltage, so it has no way to accurately calculate power factor or kWh.

​Here is the formula our meters use to calculate kWh:

​kWh = volts x amps x power factor

So you can see without accurate volts and power factor, your OWL meter is guessing at best. If you still want to make sure your EKM meter is accurate, you can take it to your local Department of Weights and Measures and have them test it for you.


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