Electronics > Beginners

Clamp Meters and Apparent Power

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EPAIII:
Yes, some time ago I was pleasantly surprised to find out that modern clamp-on meters can measure both AC and DC. They use Hall Effect sensors. And this is not just expensive ones, I have one that cost only \$40, USD that has this capability. Not highly accurate, but it does measure DC current as well as AC.

It does have a digital VOM built in and I need to read the instructions again to see if it can measure power.

Isn't modern tech wonderful?

--- Quote from: BeBuLamar on March 22, 2023, 10:48:02 pm ---
--- Quote from: wasedadoc on March 22, 2023, 07:49:53 pm ---

2.  The clamp does not measure Direct Current, only AC.

3.  Small DC currents can only be measured by putting the meter in series in the same way as a conventional multimeter.

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Many clamps can measure DC current. Fewer clamps can measure small DC current but some can measure down to 5mA.

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coppice:

--- Quote from: Ali uxama on April 06, 2023, 08:46:03 am ---Hi,

Thank you for sharing your understanding of AC current meters. You are correct in saying that a typical current meter, whether it's a clamp meter or a moving iron 2-wire meter, will register the reactive current flowing into and out of an AC device that is heavily reactive and consumes a lot of apparent power.

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There is no such thing as reactive current. There is only current. The concepts of active, reactive and apparent are power issues, not current or voltage issues. Until you start integrating voltage and current over time, to measure power, active, reactive and apparent have no meaning at all. Things consume active power. They do not consume reactive power. Apparent power is a mish mash (the third side of a triangle for pure sine wave voltage and current) of active and reactive power. The active component is consumed, and the reactive component is not. If its consumed it can end up as heat somewhere down the line. Reactive power can't heat anything. Most confusion in understanding these concepts comes from this kind of sloppy use of words. Use words more precisely and it all falls into place.

paulca:
I think that's why they call it "apparent", apparently.

Anyway.  I have had a coil clamp meter on my mains electrical tails for 3 years.  The "total power returned" is -1.2kWh.  That's after a net consumed of something like 18,000kWh can't remember.

It's interesting and maybe relevant because that figure should be 0.  I do not have an generation equipment.  The meter account for all 3, as it has a current AND voltage tap.  So it's not reactive power.  At some point my house pushed current outward that it did not get back.  Where did it come from? Where did it go?  (Cotton eye joe!).

The reality is, it's probably just aggregate software rounding errors.

Just in case nobody has reminded folks yet... a current coil/clamp around a main cable that is unloaded/unburdened is extremely dangerous.

coppice:

--- Quote from: paulca on April 06, 2023, 10:54:59 am ---Just in case nobody has reminded folks yet... a current coil/clamp around a main cable that is unloaded/unburdened is extremely dangerous.

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Most clamp on CTs have a built in burden resistor, so its harmless to leave them unconnected.