Negative Ohms and reselling cable?

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  #1  
Old 10-24-15, 05:10 PM
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Question Negative Ohms and reselling cable?

Hi guys,

So I am trying to get into and learn about the wonderful world of electricity.

First question: I bought some 2 gauge cable the other day. Today I soldered terminals on the ends. Entire length is about 3 feet. I used my new Fluke RMS 117 meter to test the Ohms resistance. I got a reading ranging from negative -0.2 to -0.1. Is there something wrong or did I do everything correct?\

Also side question, is it legal to buy bulk insulated cable and modify it by, say, adding terminals to the end and resell for profit?
 
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Old 10-24-15, 05:16 PM
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is it legal to buy bulk insulated cable and modify it by, say, adding terminals to the end and resell for profit?
I don't see why not.

I don't think a digital ohmmeter will ever read a negative number. Are you sure it's on the ohms setting and not DC volts ?

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  #3  
Old 10-24-15, 05:28 PM
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Thank you, I was just worried about legal action from the original maker of the cable.

I am sure its on Ohms...Is it possible my 2 gauge cable is so conductive its actually amplifying energy sent through the test leads?
 
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Old 10-24-15, 05:39 PM
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What do you measure when you short the two probes together ?
You should get the same reading when checking a heavy piece of wire like that.

What do you intend to sell the cables as or for.
There is something called "fitness of merchantability" and "implied warranty"

Warranty of merchantability legal definition
 
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Old 10-24-15, 06:05 PM
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When I put the probes together, I measure a 0.1 which I think is what its supposed to be. But for some reason with the wire I'm getting around -.02. I read online there is something called negative resistance?

I would like to sell the cables as jumpers with terminals attached. I do understand implied warranty so I would be QA-ing my own work and making sure there is no defects and reimburse customer if needed.

EDIT: Just out of curiosity, I took my newly made cable and touched it against a cold water pipe. I tested it with my meter and now I'm getting 0.1 ohms. Looks like there was a small amount of current lingering on my cable! Probably from when I was using my soldering iron to solder the terminals together. Cool!
 
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Old 10-24-15, 06:23 PM
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I don't ever remember seeing a negative number when in ohms mode. I'm going to have to play now.

Basically.... the ohmmeter is a DC voltage measuring mode. The resistance creates a partial short of that DC voltage and that corresponds to a certain ohms reading.

One way you could read negative is if that wire had a negative charge on it.(pretty unlikely)
If that were the case you should be able to reverse the leads and get a positive reading.

Another possible cause is running a DC voltage(your meter in ohms mode) thru two dissimilar metals...... your wire and your lugs.
 
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Old 10-24-15, 07:10 PM
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Did you zero the meter before you started? Also check the battery for resistance function (it usually is separate from the one for the meter electronics).
 

Last edited by ray2047; 10-24-15 at 08:23 PM. Reason: Clarify
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Old 10-24-15, 07:18 PM
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His Fluke will only have a single 9v battery in it.
 
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Old 10-24-15, 08:00 PM
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Okay so I took my newly made cable and touched it against a cold water pipe, grounding it. I tested it with my meter and now I'm getting 0.1 ohms. Looks like there was a small amount of current lingering on my cable...It was probably caused my my soldering because I just made another cable, got the same reading, grounded the wire, and then got the correct 0.1 ohm reading. Science...
 
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Old 10-24-15, 08:26 PM
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His Fluke will only have a single 9v battery in it
Is it also self zeroing? (Only used cheap ones from the fleamarket.)
 
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Old 10-24-15, 08:44 PM
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Yes... his Fluke is self zeroing. The more expensive ones have a provision for absolute zeroing.
 
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Old 10-24-15, 09:02 PM
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Dang new newfangled gadgets how can us old timers keep up.
 
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Old 10-25-15, 06:24 AM
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Ohms range is actually a dc voltmeter, with a constant current source driving the circuit. So, a negative reading says there is an external voltage present that is countering the meter's current source. It won't take much. My guess is not "lingering current", but more likely a thermoelectric effect due to heat across dissimilar metals. lead, tin, copper. By the time you touched the water pipe, the joint cooled down.
 
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Old 10-25-15, 08:07 AM
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Or that roll of superconducting copper has been found with the stored energy. Might be worth seeing the reward.
 
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Old 10-26-15, 06:52 AM
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Countdown to free energy manifesto...

That meter has stated resolution of 0.1 ohms and accuracy of 0.9% on the normal resistance scale, which means that any number from -0.1 to +0.1 are essentially the same reading of zero, with all variation explained by the internal operation of the meter.

fluke.com

Ohms Range/resolution 600.0 Ω / 0.1 Ω
6.000 kΩ / 0.001 kΩ
60.00 kΩ / 0.01 kΩ
600.0 kΩ / 0.1 kΩ
6.000 MΩ / 0.001 MΩ
Accuracy 0.9% + 1
Range/resolution 40.00 MΩ / 0.01 MΩ
Accuracy 5% + 2

Thank you, I was just worried about legal action from the original maker of the cable.
The original maker would have no claim against you unless you're using their brands in your advertising, but one of your customers could have a claim if they used one of your cables and it was found to be the cause of an injury or damage. I also suspect that modifying and reselling the cable may void the UL listing, making it non-compliant to install in any building premises wiring system. Other purposes may still be permitted like low voltage or automotive without the UL mark. I believe there is some provision for assembling a device out of all UL listed components having some sort of "pass through" listing, but you would still probably carry some liability for your portion of the work done on the final assembly.
 

Last edited by ibpooks; 10-26-15 at 08:29 AM.
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