Amtrak Signal Maintenance Training – Level 1 (SMT-1) Practice Test

Which color indicates AC high voltage?

Green Red Blue Yellow

Correct Answer:

Red

Explanation:

In electrical safety, colors are used as quick signals to show what kind of hazard you’re dealing with. Red is the color most commonly used to indicate high-voltage, energized AC circuits in railroad traction systems. That strong, attention-grabbing color tells you to treat the equipment as live and to follow proper de-energizing procedures, lockout/tagout, and appropriate PPE before touching anything. Green is typically used for grounding or safe paths, while blue and yellow are used for other signaling or voltage indications in different contexts, so they don’t specifically denote AC high voltage.

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