A construction crew is working near an overhead power line. If the line voltage is unknown, what is the minimum safe clearance distance required?
Correct Answer
B) 10 feet
When voltage is unknown, OSHA requires a minimum 10-foot clearance from overhead power lines for construction equipment and workers.
Why This Is the Correct Answer
OSHA 29 CFR 1926.416(a)(1) specifies that when voltage is unknown, workers and equipment must maintain a minimum clearance of 10 feet from overhead power lines. This 10-foot default applies specifically because the voltage is unknown — without knowing the voltage, you cannot use the voltage-specific clearance tables, so OSHA defaults to the general 10-foot rule. This clearance applies to all tools, equipment, and workers.
Why the Other Options Are Wrong
Option A: 20 feet
20 feet is the minimum clearance required for lines operating at voltages above 350 kV up to 500 kV, or in some references for cranes near high-voltage lines. It is not the general unknown-voltage default for construction crews.
Option C: 6 feet
6 feet is not an OSHA standard clearance distance for power lines. It may be confused with other clearance requirements (such as minimum working space around electrical panels) but does not apply to overhead power line proximity.
Option D: 15 feet
15 feet applies to specific voltage ranges (over 50 kV up to 200 kV in some regulations) or to crane operations near certain power line voltages. It is not the standard unknown-voltage default clearance for general construction work.
Memory Technique
Power line unknown = 10 feet minimum. Think of 10 as the baseline safety number for electrical clearances. 'When in doubt, stay 10 out.' Cranes and larger equipment have stricter requirements, but for workers and hand tools, 10 feet is the unknown-voltage default.
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