Glossary Cable Sizing

What Is a Continuous Load and Why Does It Get a Safety Factor

A quick-reference definition of continuous load, and why it triggers extra design margin that a non-continuous load does not.

"Continuous load" is a specific technical term, not just a general description of something that "runs a lot" — and the specific definition determines whether the 1.25× safety margin applies.

The Working Definition

A continuous load is one expected to operate at or near its maximum current for an extended period — commonly defined around a three-hour threshold in most codes' framing. The key idea is sustained, near-full-current operation, not brief peaks or intermittent cycling.

Common Examples

• Lighting circuits that stay illuminated for hours
• HVAC compressors running long duty cycles
• Solar PV array output during a sunny day — hours of near-rated current production

What's Typically Not Continuous

A load that cycles briefly and then rests — a momentary appliance, a short-duration process load — doesn't automatically get the same continuous-load treatment, though it may still have its own separate sizing consideration (a motor's starting surge, for instance).

Why It Matters

A conductor and its protective device sized without accounting for genuinely continuous operation can run at a sustained thermal stress level the design never actually accounted for — the safety margin exists specifically to prevent that gap.

Engr. Jason Morales — Founder, SolarEnergyPH & OhmWorks

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