Current limits when grouping to a single output.

So as I understand in this tutorial, you have two wires capable of handling 6-8A each, for a Fan that will draw 12A, and you set the trigger at 150% which is 18A - This I understand.

In the next statement you mention if current capacity of the wire is lower than the draw, then to use that capacity instead. In this example you have used two 8A wires. So what is there to protect the wire if one of the connections fails? As you will have your trigger at 18A, and a cable capable of just 8A?

Which leads me to my actual question (apologies I have mentioned this somewhere else on the forum but felt here was more appropriate) If i want to group the ECU (1A), Gauge (5A) and a 12v socket (10A) for example onto a single 25A output. I set the limmit to 24A which is 150%. Would I have to run a #12 wire to each component now? Or if I run a #22 wire to the ECU is this not dangerous?

In your worked example you have the 4x 2A lambda's and 1A thermocouples grouped, and protected with 15A - a similar situation, how do you wire this?

Apologies if there is something I'm not getting as it seems to me that the two 'rules' so to speak, contradict each other?

Many thanks, Dan