Electrical Safety, Tools, and Testing
Working safely
NFPA 70E governs workplace electrical safety: shock and arc-flash risk assessment, approach boundaries, personal protective equipment, and energized-work permits. The default is to de-energize, lock out and tag out, verify the absence of voltage, and apply temporary protective grounds where required. Verification means testing with an instrument proven on a known live source before and after the test - a dead-circuit check with an unproven meter is not verification. Arc-flash incident energy grows with available fault current and clearing time, and that energy determines the PPE category and arc-rated clothing needed.
Instruments and their limits
Know what each tool measures and where it may safely be used. Multimeters and testers carry CAT ratings: CAT III for panelboards and feeders, CAT IV for service entrances and outdoor conductors. Using an under-rated meter at the service is a classic exam trap. Ohmmeters and megohmmeters work only on de-energized, isolated circuits; insulation-resistance tests require disconnecting sensitive equipment, and equipment rated 600 V is commonly tested at 500 V DC, with roughly 1 MΩ plus 1 MΩ per kV as a common minimum guideline. Clamp meters read current without opening the circuit. Ground resistance is measured by fall-of-potential or clamp-on methods. A GFCI tester confirms trip function only - it does not prove the equipment grounding path.
Habits questions reward
Test before touch, keep one hand free where practical, use insulated tools, inspect cords and PPE, and treat unknown conductors as energized. Document test results and tag equipment out of service when it fails.
Worked example: testing at a 480 V feeder termination calls for at least a CAT III meter; at the service entrance or meter socket, CAT IV is required.