IAC AFL or AFLR? Select MV Switchgear from the Actual Room Layout and Arc-Exhaust Arrangement

What an IAC designation actually tells you

The current IEC reference is IEC 62271-200:2021+AMD1:2024, covering prefabricated AC metal-enclosed switchgear and controlgear above 1 kV and up to and including 52 kV. IAC is an optional classification established by testing a defined assembly under defined conditions. A project designation therefore needs more detail than “arc resistant.”

For example:

IAC A FLR 25 kA 1 s

Accessibility Type A and Type B describe who may approach the equipment; they are not different names for AFL and AFLR. Their IEC test arrangements and indicator positions differ. Type B uses the arrangement for unrestricted public access. A locked Type A enclosure does not become Type B.

Likewise, F, L and R identify the tested accessible sides. They do not describe the direction in which gas is discharged. An AFLR panel may still vent upward into a room, through a top duct, or through an engineered duct to the outside, depending on the tested design.

IAC, arc-flash assessment, LSC and PM/PI answer different questions

These terms are often placed in the same data sheet, but each addresses a separate issue.

An LSC2B-PM assembly supports defined service continuity and uses metal partitions, yet still needs a separately stated IAC classification. An IAC-classified assembly does not automatically have LSC2B-PM construction.

IAC cannot replace an arc-flash study. IEC testing evaluates enclosure behaviour against prescribed criteria. A site study evaluates the electrical system and worker exposure. ABB’s mitigation guidance likewise treats passive enclosure performance, active arc detection and incident-energy reduction as distinct measures.

Select the accessible sides from the real room

Mark every place where an authorized person or member of the public can stand during operation, inspection, testing and maintenance. Then select the IAC sides from that access map.

Does back-to-wall installation make AFL sufficient?

It can, for a product verified in that arrangement and a room where the rear remains inaccessible. ABB’s ZX0.2 catalogue gives a product-specific example: its wall-installation configuration is IAC AFL, while its free-standing configuration is IAC AFLR. Both rely on the stated pressure-relief arrangement.

The classification of one physical arrangement cannot be transferred to another without evidence.

Follow the hot-gas path all the way to a safe discharge point

During an internal arc, hot gases and particles follow the path provided by roof flaps, absorbers, a plenum, a rear channel or an external duct. Each option changes the room interface.

The design team should trace this route on the GA:

1. faulted compartment and pressure-relief opening;
2. internal channel, room volume or external duct;
3. terminal discharge point and its exclusion zone.

A beam, cable tray, light, ventilation duct or fire pipe can obstruct a flap or redirect gas toward an aisle. An external outlet can also face a walkway, door or air intake.

Schneider Electric’s MCSeT documents show different ceiling heights and rear clearances for specific internal- and external-exhaust arrangements. They also state that building safety under internal-arc pressure and required room relief openings need separate consideration. The published dimensions belong to MCSeT; ceiling height and civil design remain product-specific.

The room designer should therefore confirm:

• minimum clear height above the completed switchgear, including LV compartments and arc duct;
• obstruction-free space for pressure flaps;
• duct section, supports, bends and route limits;
• outlet location and weather protection;
• allowable pressure load on walls, doors, ceilings and penetrations;
• room pressure-relief openings and fire stopping;
• safe access after an event.

Illustrative room scenario: the rear aisle changes the answer

Consider a nine-panel, 12 kV indoor lineup in a restricted substation. The initial civil drawing shows:

• 21 kA prospective short-circuit current at the MV bus;
• 0.55 s maximum total clearing time for the relevant bus or feeder fault, including breaker interruption;
• a 1,000 mm front operating aisle;
• an 800 mm rear maintenance aisle with a locked access door;
• exposed lineup ends;
• 3,300 mm clear room height;
• a proposed top duct discharging through the external wall.

The locked rear door does not remove the rear from consideration. Authorized personnel can enter, so the selection basis is Accessibility Type A with F, L and R coverage. IAC A FLR 25 kA 1 s would exceed the stated inputs in this simplified example. Approval still requires evidence for the offered assembly and exact duct arrangement.

If the owner deletes the rear aisle, AFL may become feasible only if the product supports front access, the rear becomes permanently inaccessible, the wall clearance matches the verified arrangement and maintenance remains practical. The revised GA must show the duct, cable entries and fixings.

If clearing time rises to 1.2 s or fault duty exceeds 25 kA, the example classification no longer matches. Both changes require technical review.

Procurement and design confirmation table

Issue this information with the enquiry and require the supplier to return evidence against it.

How to review a Minglang reference configuration

The public ML-AIS1224 product page lists IAC AFLR 31.5 kA/1 s for its documented 12 kV reference configuration. This is a catalogue reference for early selection. For a project offer, request confirmation that the available evidence applies to the proposed panel types, construction, ratings, end covers, installation arrangement and pressure-relief solution. Do not assume that the public reference covers every 12 kV or 24 kV configuration.

The ML-AIS405 product page presents a project-engineered 40.5 kV platform and a reference dimensional envelope. Its public reference data does not state an IAC rating. The project team should request the current configuration-specific document set and should not infer an internal-arc classification from the product family or from another voltage platform.

Buyer checklist before technical bid approval

• Full designation states IAC, accessibility type, accessible sides, current and duration.
• The specified IEC 62271-200 edition is identified.
• Fault current and total protection clearing time have been issued by the system designer.
• Every accessible side is marked on the room plan.
• Back-to-wall or free-standing installation matches the supplier’s verified arrangement.
• GA shows panel height, arc duct, flap movement and minimum clear height.
• Rear and side maintenance access remains practical.
• Hot gases terminate at a safe point and cannot enter a normal escape or working route.
• Civil designer has considered room pressure, openings, doors and penetrations.
• Test evidence is mapped to the offered lineup, ratings and construction.
• LSC and PM/PI are reviewed separately from IAC.
• Site arc-flash risk assessment, operating procedure and PPE requirements remain in the project safety scope.

Frequently asked questions

1. Is AFLR always better than AFL?

AFLR covers an additional accessible face: the rear. It is necessary when the rear can be approached. A verified AFL back-to-wall installation can be appropriate where rear access is permanently excluded. Selection should follow the room and operating arrangement.

2. Does a rear aisle behind a locked door require R?

Usually yes when authorized personnel may enter that aisle while the equipment is energized. A locked door controls who enters; it does not make the rear face physically inaccessible to authorized personnel.

3. Does IAC mean the switchgear is safe for live work without PPE?

No. IAC is a conditional assembly classification. Safe work practices, risk assessment, operating procedures, remote operation where appropriate and required PPE remain applicable.

4. Is IAC the same as an arc-flash study?

No. IAC is based on an internal-arc test of a defined switchgear assembly. An arc-flash study calculates or assesses site-specific worker exposure using the electrical system, protection operation, working distance and task conditions.

5. Must the IAC current equal the switchgear short-time withstand current?

Do not assume that they are equal. They are separate declared ratings and may have different durations. Compare both values with the project duties and read them separately in the test evidence and data sheet.

6. Can an exhaust duct be added after the switchgear is selected?

Only through a manufacturer-approved arrangement supported by the applicable design and evidence. Duct cross-section, bends, joints, supports and outlet conditions affect pressure and gas flow. An unverified site modification may invalidate the intended performance.

7. Does LSC2B-PM imply IAC AFLR?

No. LSC2B addresses service continuity and PM identifies metal partitions or shutters. The IAC designation must be stated and evidenced separately.

Send the room data before asking for an IAC selection

For a configuration review, send Minglang the switchgear-room plan and section, system fault level, maximum protection clearing time, authorized/public access conditions, accessible front/side/rear faces, and the proposed arc-exhaust route and outlet. With those inputs, the engineering team can prepare a project-specific GA and identify the product documents that require applicability review.