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Low R measurement on a DMM
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nctnico:

--- Quote from: pope on March 27, 2023, 12:55:36 pm ---
--- Quote from: grumpydoc on March 27, 2023, 12:52:08 pm ---As ever, what are you trying to measure, and why?

--- End quote ---

Continuity between PE and different points of the enclosure.

--- End quote ---
AFAIK you need a special tester for that which uses high AC currents (up to tens of Amps). At least if you want to adhere to standards.
JohanH:
You could have a tiny wire or connection somewhere measuring 100 mΩ, but it won't last the short circuit current that PE is designed for. So it depends on your application. If it's for hobby use, use visually good wire connection, trust your DMM and use double fused IEC socket and you are good to go. If this is for some commercial application, it gets complicated...
BeBuLamar:
My meter has resolution down to 1 milliohm but I doubt that I can get accurate reading of a 0.2 ohms resistance.
BillyO:
On some better meters the REL function works in ohms as well.  While this helps take the lead resistance out of the measurement, it does not help with contact resistance to the DUT.  Even with a 4W Kelvin arrangement, you still need to ensure clean, low resistance contact otherwise you will still be making inaccurate measurements.
alm:
For the normal case of measuring say a low value current shunt, you'd do a four wire measurement by feeding a current, for example from a bench supply, through the resistor and measure the voltage across the resistor at its terminals (separate connections for voltage and current). Then divide the voltage by the current, and you get the resistor. For very low value resistors it helps to use a larger current, like 1A, to increase resolution.

For earthing resistance measurements there will likely be specific standards in your local electrical code. I wouldn't assume a random DIY solution would be sufficient there.
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