ohm readings


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Old 11-01-14, 01:20 PM
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ohm readings

Can someone explain OHM readings and how they relate to my multimeter?

Reason I ask, I will test for OHM between two spans of conduits on different circuits. Thinking that they are both connected to the same ground so the readings should be firm. However, the readings seem pretty erratic, jumping back and forth. I don't know what is considered good readings as my multimeter seems to be all over the place.

Ive tried other meters and even putting both probes on the same piece of conduit and the readings jump back and forth as well.

Surely I just don't understand ohm readings at all and I have just relied on the continuity alarm function to tell me stuff is connected.
 
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Old 11-01-14, 01:27 PM
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If you touch the two probes together, what do you get. It should be zero, but digital meters will sometimes jump around as you describe it, but still very close to zero. If it isn't zero or close, the probes or the meter is in trouble, sometimes batteries.

Bud
 
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Old 11-01-14, 02:37 PM
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You also might need to scrub the metal a little bit to get good contact with the probe. Even a very thin layer of oxidation on the pipe will make the ohmmeter jump around, especially if you have really sharp, pointy probes.
 
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Old 11-01-14, 02:46 PM
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So using my example of touching conduits connected to the same ground, what values should I be looking for?
 
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Old 11-01-14, 02:48 PM
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On analog multimeters you need to zero them by holding the probes together and turning the adjustment knob/wheel. On digital multimeters there is a separate battery for the ohms reading. If it is failing it may give erratic readings.
 
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Old 11-01-14, 02:50 PM
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Using the conduit as one half of your circuit.... you should see anywhere from 0 to 10 ohms.
In an ideal world you would want very close to 0 ohms.
 
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Old 11-18-14, 01:29 PM
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Most of the time when check OHM... Im showing less than 1... like .05 etc.

However, a few times I checking stuff (For instance duct work of furnace with furnace junction box) I am showsing NEGATIVE .05 OHM. -.05.

What is the negative?
Is that what people refer as infinity?
 
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Old 11-18-14, 01:38 PM
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It's just a meter quirk, effectively zero. Anything more precise than whole numbers, is effectively meaningless unless you're using an expensive lab-calibrated meter.
 
 

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