HSE HUB › Question of the Day archive › 4 November 2026
ASP practice question: Electrical principles
Question of the Day for Wednesday, 4 November 2026
ASP · Safety Programs and Concepts
A 120-volt branch circuit protected by a 20-ampere breaker feeds a metal-cased bench grinder at a fabrication shop. The hot conductor faults to the grinder's case. Which ground-fault return path impedance would leave the case energized without tripping the breaker?
Explanation
Fault current is I = V/Z, so an 8-ohm path carries only 120/8 = 15 A, below the 20 A breaker rating, and the grinder case stays energized at a dangerous voltage. The 2.0-ohm path is the most tempting answer because a loose fitting sounds unsafe, but it still drives 60 A, three times the breaker rating, so the breaker opens. The 0.3 and 1.0 ohm paths drive 400 A and 120 A and trip the breaker quickly, which is why the ground path must be permanent, continuous and effective. Source: 29 CFR 1910.304(g)(5) and FAA-H-8083-30B, Aviation Maintenance Technician Handbook General (2023), Chapter 12, Fundamentals of Electricity and Electronics (Ohm's law).Practise more questions like this
Studying for the ASP? The ASP11 blueprint explained · ASP practice questions by domain · ASP vs CSP · All guides
Unofficial study aid: not affiliated with, endorsed by, or connected to the Board of Certified Safety Professionals (BCSP). ASP and CSP are trademarks of BCSP. Questions are original study items written for HSE HUB.