Internal Arc Classification (IAC) records the performance of a metal-enclosed switchgear assembly during a specified internal-arc test. A complete claim includes accessibility type, accessible sides, test current and duration. The letters IAC alone do not describe the result.

Learning objectives

Read an IAC designation correctly, understand the installation conditions that support it and separate product classification from a site-specific arc-flash risk assessment.

Core engineering principles

Accessibility type identifies who may be present

The declared accessibility type relates to the intended personnel and controlled area around the assembly. It must be read with the manufacturer’s installation and operating instructions.

AFLR identifies tested accessible sides

Letters such as A, F, L and R communicate the accessibility basis and the front, lateral and rear sides included in the declaration. A front-only result should never be represented as four-sided performance.

Current and duration are essential

The test current and arc duration define the imposed energy and pressure development. A 20 kA, 0.5 s classification is not equivalent to 25 kA, 1 s, even if enclosure appearance is identical.

Room interfaces affect performance

Ceiling height, wall distance, pressure-relief flaps, ducts, absorbers and cable openings influence gas flow. Blocking a relief path or installing the board outside the tested arrangement can invalidate the intended protection.

IAC does not guarantee zero injury

The classification evaluates specified criteria under a defined test. It does not prove every possible fault location, arc duration, maintenance state or worker position, and it does not replace risk reduction or safe work practice.

Engineering application method

  1. Step 1: Record the full IAC designation, current, duration and accessible sides.
  2. Step 2: Compare the test arrangement with the proposed room, aisle and pressure-relief system.
  3. Step 3: Verify extension rules for end panels, ducts, absorbers and panel variants.
  4. Step 4: Coordinate protection clearing time and arc-detection schemes without claiming they change the nameplate classification unless formally assessed.

Practical example

A board classified IAC AFLR 25 kA 1 s with a tested pressure duct requires that duct to be installed as designed. Omitting it because the room appears large can redirect hot gases into the working area and defeats the basis of the classification.

Common mistakes

  • Quoting only “arc resistant” or “IAC”.
  • Confusing fault-current rating with arc-test current and duration.
  • Ignoring end-panel or rear-clearance conditions.
  • Treating IAC as the same as an IEEE 1584 incident-energy result.

Design and review checklist

  • Is the full IAC designation stated?
  • Are current, duration and tested sides adequate?
  • Does the building preserve relief paths and clearances?
  • Are operating states and maintenance limitations understood?
  • Is arc-flash risk assessed separately where required?

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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