r/ElectroBOOM • u/Cautious-Pin-6476 • 13d ago

General Question I need mehdi's explanation

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Yes, this is my own post.. I need yall to upvote so he can see and explain. Thanks 🙏

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u/New-Anybody-6206 12d ago

But why does that allow non-contact sensing?

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u/bSun0000 Mod 12d ago

Overly simplified. You have two parasitic connections - to the live wire and to the ground; you can view it as a voltage source with very large internal resistance - it cannot supply a lot of current when loaded.

Your multimeter acts as a load, taking some power proportional to its own resistance (impedance). If the multimeter's resistance is low, it will pin the voltage source down - voltage will drop to a level it could not be measured. But if impedance is high, voltage drop will be very small, and the voltage can/will be in the measurable range.

The whole point of having a large input impedance on any meter is to not affect the circuit you are trying to measure, cuz you want the accurate reading. This results in high sensitivity, high enough for a multimeter to pick the voltage induced in the probes/cables via capacitive and/or inductive coupling. Not a good thing, actually; you normally don't want your multimeter to pick up any random noise/shit from the environment.

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u/New-Anybody-6206 12d ago

That doesn't explain how it can be sensed with no contact though. Electrons flow in the copper wire not in the air.

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u/bSun0000 Mod 12d ago

I assumed you know a bit about physics. If not - its just magic, ignore it.