Timing tests are useful only when the measured interval is defined. Opening time, arcing time and breaking time start and end at different events; using them interchangeably can create false acceptance or false alarms.

Learning objectives

Define principal timing quantities, measure contact events consistently and interpret pole spread against manufacturer limits and system duty.

Core engineering principles

Opening time ends at contact separation

It is measured from the specified trip-command reference to separation of the arcing contacts. It does not include the subsequent arcing interval.

Arcing time runs from separation to current interruption

The arc continues until a suitable current zero. Its duration depends on command timing relative to the AC waveform as well as breaker motion.

Breaking time includes opening and arcing

This system-relevant interval extends from trip initiation to interruption in all poles under the defined conditions.

Closing and make times use different endpoints

Mechanical contact touch and establishment of current are close but distinct events, especially with prestrike. The test instrument channel definition must be stated.

Pole spread is not one universal number

Opening and closing simultaneity have separate limits. Application, controlled switching and manufacturer tolerances determine significance.

Engineering application method

  1. Step 1: Define start and end references before connecting the analyser.
  2. Step 2: Use consistent wet or dry contact channels and command pickup.
  3. Step 3: Record all three poles and auxiliary contacts.
  4. Step 4: Compare opening, closing and spread with breaker-specific limits.
  5. Step 5: Trend values under comparable voltage and mechanism conditions.

Practical example

A relay-to-current-interruption time cannot be compared directly with a manufacturer’s mechanical opening-time limit. The former includes relay output, coil pickup, contact motion and arcing; the latter may begin at coil energisation and end at contact separation.

Common mistakes

  • Calling every interval opening time.
  • Comparing wet and dry contact methods without correction.
  • Ignoring coil voltage during the test.
  • Using average time to hide one slow pole.
  • Applying another breaker model’s tolerance.

Design and review checklist

  • Are timing definitions written?
  • What event starts the timer?
  • What contact event stops it?
  • Are all pole values and spread recorded?
  • Are limits manufacturer-specific?

Standards basis and official sources

Engineering note: Verify the contracted standard edition, amendments, manufacturer evidence and project-specific studies before applying these principles to a supplied assembly.

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