OHELE reference layer
Electrical Engineering Cheat Sheets
Practical checklists for measurement, isolation, connection, protection and hazardous-area work. Use them as prompts for an approved procedure, not as a substitute for engineering judgement.
How to Use a Multimeter: Voltage, Current, Resistance and Continuity
The first decision when using a multimeter is not which button to press. It is whether the meter, leads, probes, and selected function are…
Insulation Resistance Testing: Principles, Procedure and Interpretation
Insulation resistance testing applies a controlled DC test voltage to de-energized insulation and measures the small current that flows. The instrument reports resistance, usually…
1910.147 vs 1910.333: Which OSHA LOTO Rule Applies to Electrical Work?
For U.S. general-industry work, the answer starts with the hazard and the task, not the padlock. OSHA’s 29 CFR 1910.147 covers control of hazardous…
How to Select Terminal Blocks for Electrical Panels
Select a terminal block by circuit function first, then verify conductor acceptance, electrical duty and environmental conditions. Only after those checks should you finalize…
ATEX Lighting Zones for Hazardous Areas: A Practical Selection Guide
ATEX lighting selection starts with the area classification and the substance hazard—not with a luminaire catalogue. A compliant decision normally needs the classified zone,…