Circuit Theory

A: A feels good if you stop at "CAN is low current" and forget the round-trip. 0.35 mm² copper is ~0.05 Ω/m. Eight meters round-trip gives ~0.4 Ω. At 60 mA, V = IR lands around 24 mV per meter pair, totaling just under 0.1 V. C jumps a decimal; you'd need amps, not tens of milliamps. D confuses duty cycle with DC drop — continuity doesn't amplify Ohm's law.

A: A is the gut reaction — lower Vin feels stressful — but P = (Vin − Vout)·I. As Vin falls, dissipation falls. C forgets the pass element physics; output power isn't what heats the die. D assumes an ideal switch; linear regulators still burn power until true dropout, and that's where regulation fails. The right move is watching headroom, not heatsink temperature.

A: B looks disciplined but measuring ground offset without load tells you very little. A risks bricking hardware before basics. D skips current limiting, a classic field mistake. C puts a leash on fault energy first, then checks the rail doing what it's supposed to, and only then worries about millivolt-level ground shifts.

A: A, C, and D are exactly why the fuse exists — too much current for too long. B slips through because the MOSFET can cook itself at currents below fuse melt I²t, especially in linear mode. The fuse stays happy while silicon dies. That's how you get smoke with an intact fuse.