I just received a stranded 12 AWG cable from China in the mail. I can't understand why its resistance is so high. The first question you will ask is, "How do you know its resistance is way too high?"
So, here is what I did:
I confirmed that the cable is definitely made of tin plated copper and not Copper Clad Aluminum (CCA) (Tested with a lighter, which melted off the tin to reveal the copper underneath a single strand.)
The cable geometry is 65/30 (65 strands of 30 AWG wire).
The resistance I am measuring is 0.01121 ohms per meter. This is way too high for 12 AWG copper stranded cable with a 65/30 geometry.
The cable diameter is in fact consistent with 12 AWG (2.48 mm diameter for all strands as bundled).
Here is how I measured the resistance of 0.01121 ohms per meter. I double checked this resistance several different ways:
- I took a 4-wire kelvin measurement
- I used two HP lab power supplies current reading (1 A)
- I used a Fluke 8842A to measure the current to confirm (1 A)
- I used a calibrated HP 3456A to measure voltage to confirm 0.0588 V at 1 A
Bottom line, the cable is 0.01121 ohms per meter, 11.21 ohms per km, 3.41695 ohms per 1000 ft.
Now, let's get to the bottom line:
WTF? The cable's resistance is twice as high as it should be! What could possibly be causing this?