Determine accuracy of Shelly Pro 3EM?

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1

I just got a new (smart) power meter from my local utility, and around the same time installed a Shelly Pro 3EM which is installed with two clamps on the power coming into the home (USA split phase) - and feeding data into HA.

Once I have a couple months of data to compare the two - if they are different - how would I determine which one is inaccurate? That leads to the question, how accurate are clamps when used to measure power? Is that an estimate rather than a more accurate professional way of measuring the power usage (I do not know the different methods of power usage measurement)…?

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Clamps will likely always be less accurate than directly metering the power. If the power company is actually measuring the line then I would trust that more. I think the clamps are mostly billed as “close but not exact” to give you a general idea.

The same concept as measuring your BMI on your smart digital scale - it’s inaccurate but it is consistent so you can still determine trends but shouldn’t change your life based on the value it gives you.

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3

Thank you. Do you know the various methods of electric power usage measurement? Are there more than two?

4

Well, as far as I know there has always been just one - so they invented the clamps so you don’t have to pay someone to install the meter for you.

A psychic might could tell you, I’ve never asked :stuck_out_tongue_winking_eye:.

But, seriously, I think those are really the only ways.

5

Thank you. Do you know if the clamps tend to run over or under the usage, or not sure (if I knew then I could adjust for accuracy)?

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I don’t really know to be honest, but it seems like it would be easy to test by clamping the romex as needed and then a multimeter testing the actual voltage being sent to a device plugged into the socket.

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Yes but my clamps are on the large cables as they come into the home so I need to measure it there, and not measuring the voltage per se, but the power that is being consumed. I can do it but am not sure how to do it. I have a simple inexpensive meter but it only measures voltage. I’d rather not buy more tools that I use only once…

8

Most multimeters also measure amps, volts and watts. What power are you after?

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I am not sure - I want to be able to at least validate and reconcile the measurements against my power bill -

10

It says right on their site:

The shelly pro 3em has class B accuracy which is 1%.
However i found it to be a little less, maybe around 0.7-0.8%