Suppose you have two extension cords. One is a nice, thick #10 50′ cord with good ends, and the other is a crappy #14 25′ cord. Unfortunately, you need to connect them both to get to your drill 75′ away.

Which do you connect to the plug, and which to the drill?

Come up with what you think the answer is. I will wait.

If you said connect the nice one first (to the plug), you would agree with 95% of people.

But here's the real answer: IT MAKES NO DIFFERENCE.

An extension cord creates a complete circuit, from hot 120v down both cords to the load (the drill) and back through both neutrals to the neutral plug terminal.

The resistance (opposition to current) and ampacity (safe current carrying capacity) of the circuit are for the entire circuit—period.

We can often fall into the trap of thinking about electricity in terms of points in the circuit. There are good reasons for that when we're diagnosing broken equipment. Still, there's more to a circuit than whatever is between two points of differing electrical charges (potential difference); the amps, ampacity, voltage drop, watts, and resistance of the entire circuit are really what matter.

An electrical circuit is only as good as its weakest link. Unlike sausage… because all sausage links are delicious.

—Bryan