Electronics > Projects, Designs, and Technical Stuff

KWh meter - is there such a thing as a non-contact one?

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Merlysys:
Its to monitor energy use of a subpanel(upto 60A at 120V). I could buy a KWh meter and hook in between main power source (120V) and subpanel.

But it would be easier if it just has a current clamp so I could wrap it around a wire. Such a device should have a voltage set for 120V but even if it only displays amount of current flowed (in coulombs or whatever unit) in a given period I could convert that to KWh.

If nobody makes such a thing what suggestions you have?

Zero999:
The short answer is no.

Why? It's not possible to accurately measure voltage, without a physical connection to the cable. Capacitive coupling could theoretically be used, but it's only accurate if the area of the conductor and distance are exact and the dielectric constant of the insulator is precisely known.

The only way would be to fix the voltage probe to the cable, calibrate it against a meter connected directly to the cable and ensure the voltage probe and cable are never moved afterwards, otherwise it will need to be recalibrated. Drift would still be an issue, since the dielectric constant of the cable will change due to changes in moisture and atmospheric humidity, which will limit long term accuracy.

rstofer:
Amps will only get you kVA (with an assumed voltage), you need to account for power factor to get to kW and the only way you are going to do that is to measure the phase angle between the voltage and current.

soldar:
Yes, you need to measure voltage. Why can't you connect to the wires to measure voltage?

Someone:

--- Quote from: Merlysys on April 02, 2019, 02:48:48 pm ---Its to monitor energy use of a subpanel(upto 60A at 120V). I could buy a KWh meter and hook in between main power source (120V) and subpanel.

But it would be easier if it just has a current clamp so I could wrap it around a wire. Such a device should have a voltage set for 120V but even if it only displays amount of current flowed (in coulombs or whatever unit) in a given period I could convert that to KWh.

If nobody makes such a thing what suggestions you have?

--- End quote ---
If you don't mind the inaccuracy from missing the imaginary power they do exist:
https://au.rs-online.com/web/p/digital-power-meters/8724666/
Plenty of similar cheap clamp meters around, unlike the naysayers above sometimes an estimate of the power consumption is fine.

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