Wouldn't it have been more informative to test the wires individually under the same conditions and record time to "failure"?

 

Yes, or at least run them in series so the same current is passing through both wires.

 

There is no functional information derived from this “test”. It only shows that proportionally, the heavier gauge wire gets hotter. It is carrying more current in this parallel circuit. This is because a smaller wire has higher resistance than a larger wire of equal length. The short wires used in this “test” minimizes that difference, but there will still be some.

The surface area of the larger wire is proportionally less than that of the smaller wire. This means less area to transfer the heat to the surrounding air. The larger wire is 2.4 times larger in cross section area yet only 1.55 times larger in surface area.


Another variable in this “test” that could affect the outcome would be the resistance at each point of the test wire assemblies. The crimp connections on the wire ends and the connections to the bus bars.

In all, just another type of YouTube clickbait.

 

After watching the video he clearly states he is testing the corner case of two wires in parallel to share the current, in which one is smaller in diameter than the other. He is proving the thicker one will fail first which is not the intuitive answer. In summery the thicker wire is passing more current as is expected (lower resistance) but because its ratio of surface area to volume (simplified interaction) is not as high as the smaller wire it is less able to dissipate this heat to the air and therefore gets hotter and melts first. This is a well done test. To give possible context on why this video was shared, in the rare case multiple parallel wires are required due to routing constraints it must be of the same gauge wire. Do not run wires between the same two points in parallel comprised of different gauges. In general all wiring should be a single conductor from one point to another, in which case this test provides no helpful data.

This is NOT a test of given the identical current which one melts first, which is what we are mostly concerned with in van builds (sizing a single wire for the load). In that case the smaller wire will always melt much sooner.

 

After watching the video he clearly states he is testing the corner case of two wires in parallel to share the current, in which one is smaller in diameter than the other.
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Well described. I thought it was a useful test. Logically, I know the larger cable has lower resistance and thus likely will be more current; but I wouldn't have considered whether it would fail first. A current-measurement on both simultaneously would have been super interesting to add.

 

If one has ever pondered an ampacity chart, the answer as to which wire size fails first is quite clear. Larger wires are proportionally rated at lower ampacity than smaller wires. It is particularly easy with metric wire sizes since it is measured in cross section area.

 

From what I see the distribution of current remains solid (essentially a voltage divider) 34% of current across 2.5 mm² 66% of current across 6 mm². At the last setting the 6 mm² wire is carrying 167 amps or 2.92 times the expected ampacity rating (57 amps at 90°C). the 2.5 mm² is carrying 83 amps or 2.4 times the expected ampacity rating (34 amps at 90°C).

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A loose connection can have a similar non intuitive effect, with parallel paths.

 

What is the Voltage? How are you generating this HIGH current?