Which of these is considered an excessive voltage drop? 1.2V across the circuit protection

• A. 0.2V across protection
• B. 0.5V across protection
• C. 1.2V across circuit protection
• D. 2.0V across the protection

Answer: (C)

When a protection device (like a fuse or circuit breaker) is in good condition, it should pass current with very little resistance, so only a tiny amount of voltage is dropped across it. A large voltage drop on that path means there’s extra resistance somewhere in the protection path, which wastes power as heat and starves the downstream load of voltage. In automotive practice, only a small drop—typically a few tenths of a volt (0.2 to 0.5 V or so)—is considered acceptable. A drop of 1.2 V across the protection is well beyond that, signaling an abnormal or degraded path such as a loose connection, corrosion, a damaged protection device, or undersized wiring. This level of drop can cause components to underperform and the protection path to heat up, so it’s considered excessive. If you ever see 2.0 V, that would be even more severe, reinforcing the same idea that the protection path is not conducting properly.