MCC Panels

Automatic Transfer Switch (ATS) Panel — Arc Flash Protection (IEC 61641)

Arc Flash Protection (IEC 61641) compliance requirements, testing procedures, and design considerations for Automatic Transfer Switch (ATS) Panel assemblies.

Automatic Transfer Switch (ATS) Panel — Arc Flash Protection (IEC 61641)

Overview

Automatic Transfer Switch (ATS) Panel assemblies intended for arc flash protection in accordance with IEC 61641 must be engineered as fully coordinated low-voltage switchgear assemblies, not as a collection of individual devices. The core objective is to contain and control the effects of an internal arc fault so that personnel, adjacent equipment, and the installation environment are protected during source transfer, bypass, or isolation operations. In practical ATS applications, the assembly may include two utility or utility-generator incomers, mechanically or electrically interlocked switching devices, motorized changeover mechanisms, bypass/isolation sections, control relays, metering, protection relays, and communication modules. Depending on the rating, the main switching devices may be ACBs up to 6300 A, MCCBs up to 1600 A, or heavy-duty contactor-based transfer solutions for smaller systems, all selected and coordinated under IEC 60947 series requirements. IEC 61641 is the dedicated standard for internal arc testing of low-voltage switchgear and controlgear assemblies. Unlike IEC 61439-1 and IEC 61439-2, which govern general design verification of assemblies, IEC 61641 focuses on behavior during an internal arcing fault: containment, pressure relief, door security, arc gas ejection, accessibility, and the integrity of the assembly after the fault. For ATS panels, this means the enclosure structure, compartmentalization, busbar supports, cable entry system, and mechanical interlocks must be validated as a complete configuration. Common design features include reinforced doors, pressure release channels, top-mounted arc exhaust ducts, segregated source compartments, arc-resistant shutters, and ejection-proof latching hardware. Where the assembly uses Forms of Internal Separation such as Form 2, Form 3b, or Form 4b, the separation strategy must be consistent with the tested arrangement and documented in the build record. The compliance pathway generally starts with a verified design under IEC 61439-1 and the applicable part of the series, most often IEC 61439-2 for power switchgear and controlgear assemblies, with performance and temperature-rise verification aligned to the declared rated current and short-circuit withstand rating. The arc-resistant claim under IEC 61641 then requires type-tested evidence on a representative ATS configuration. Typical test parameters include the declared arcing current, arc duration, accessibility class, and the fault location inside the incomer or transfer compartment. A compliant assembly may be declared for ratings such as 800 A, 1250 A, 2500 A, or higher, provided the tested arrangement matches the manufactured design closely enough to preserve validity. Component selection is critical. Protection relays, undervoltage releases, control power supplies, shunt trips, and motor operators must be arranged to avoid vulnerable cable paths and unprotected auxiliary wiring in the arc zone. If the ATS panel interfaces with VFDs, soft starters, or essential service feeders, thermal dissipation and fault-energy coordination become even more important because these devices can influence internal pressure, cable routing, and ventilation openings. In special environments, additional references may apply, including IEC 61439-3 for distribution boards, IEC 61439-6 for busbar trunking interfaces, IEC 60079 for hazardous areas, and IEC 61641 for post-fault accessibility and inspection requirements. Where arc fault containment is part of an overall safety strategy, protection coordination with upstream ACBs or MCCBs, properly graded trip settings, and maintained short-circuit ratings are essential. For EPC contractors, data centers, hospitals, airports, water treatment plants, and industrial process facilities, an IEC 61641-compliant ATS panel supports safer source transfer and improved continuity of service. Documentation should include the tested configuration, bill of materials, mechanical drawings, arc fault certificate or test report, installation limits, maintenance instructions, and any re-certification triggers resulting from dimensional or component changes. Patrion in Turkey, through mccpanels.com, supports design verification, arc-resistant construction detailing, and certification-ready documentation for ATS panel assemblies, with certification available on request.

Key Features

  • Arc Flash Protection (IEC 61641) compliance pathway for Automatic Transfer Switch (ATS) Panel
  • Design verification and testing requirements
  • Documentation and certification procedures
  • Component selection for standard compliance
  • Ongoing compliance maintenance and re-certification

Specifications

PropertyValue
Panel TypeAutomatic Transfer Switch (ATS) Panel
StandardArc Flash Protection (IEC 61641)
ComplianceDesign verified
CertificationAvailable on request

Other Standards for Automatic Transfer Switch (ATS) Panel

IEC 61439-2 (PSC)

Power switchgear and controlgear assemblies — main compliance standard

Seismic Qualification (IEEE 693/IBC)

Earthquake resistance verification for critical facilities

UL 891 / CSA C22.2

North American switchboard safety standards

Other Panels Certified to Arc Flash Protection (IEC 61641)

Main Distribution Board (MDB)

Primary power distribution from transformer to sub-circuits. Rated up to 6300A. Houses main incoming breaker, bus-section, and outgoing feeders.

Power Control Center (PCC)

High-capacity power distribution for industrial facilities. Controls and distributes incoming power to MCC, APFC, and downstream loads.

Motor Control Center (MCC)

Centralized motor control with starters, contactors, overloads, and VFDs in standardized withdrawable/fixed functional units.

Busbar Trunking System (BTS)

Prefabricated busbar distribution per IEC 61439-6. Sandwich or air-insulated, aluminum or copper.

Custom Engineered Panel

Bespoke panel assemblies for non-standard requirements — special ratings, unusual form factors, multi-function combinations.

Frequently Asked Questions

IEC 61641 certification indicates that the ATS panel assembly has been tested for internal arc fault behavior under defined conditions. The standard evaluates whether the enclosure contains the arc, limits dangerous ejection of hot gases and particles, and protects personnel at the declared accessibility side. For ATS systems, this is especially important because source transfer equipment often combines incomers, interlocking, control wiring, and bypass sections in one enclosure. Compliance is normally demonstrated by type testing on a representative configuration, then maintained through strict design control. The panel must also remain consistent with IEC 61439-1 and IEC 61439-2 for general assembly verification and with IEC 60947 for switching devices such as ACBs, MCCBs, and contactors.
An internal arc test under IEC 61641 is performed on a representative ATS assembly using a prescribed fault arrangement, arcing current, and fault duration. The test verifies whether the enclosure remains safe for the declared accessibility class and whether doors, covers, and relief paths perform as intended. For ATS panels, the test often focuses on the incomer or transfer compartment, since that is where switching and busbar energy are concentrated. The tested configuration must closely match the manufactured design, including enclosure dimensions, ventilation openings, busbar supports, and door hardware. Test records should be retained with the project documentation, along with the declared short-circuit ratings and the exact component list used during validation.
A compliant ATS panel commonly includes ACBs or MCCBs for incoming source switching, electrically or mechanically interlocked transfer mechanisms, motor operators, control relays, metering devices, protection relays, auxiliary contact blocks, and control power supplies. For higher continuity applications, a bypass/isolation section may also be included. All devices should be selected under IEC 60947 and arranged so that auxiliary wiring is kept out of vulnerable arc zones where possible. If the panel also feeds VFDs or soft starters, additional thermal and cable-routing checks are needed. The enclosure, busbar system, and compartmentalization must support the tested arc-resistant configuration and the declared rated current and short-circuit withstand rating.
Yes, in practice they often do. IEC 61439-1 provides the general rules for low-voltage switchgear and controlgear assemblies, including design verification, temperature rise, dielectric properties, and short-circuit performance. IEC 61439-2 is typically the product-specific standard for power switchgear assemblies, which is where most ATS panels are classified. IEC 61641 is an additional internal arc testing standard that addresses the behavior of the assembly under arc fault conditions. A panel may be fully compliant with IEC 61439 but still not qualify as arc-resistant under IEC 61641. For arc flash protection claims, both the general assembly verification and the arc test evidence are important.
The recommended form of separation depends on the tested design, but many arc-resistant ATS panels use compartmentalized arrangements comparable to Form 3b or Form 4b concepts, with source incomers, transfer devices, busbars, and auxiliaries isolated as much as practical. The key point is that the internal layout must match the verified configuration used in the IEC 61641 test. Separation helps limit arc propagation and protects adjacent compartments, but it does not by itself guarantee arc resistance. The enclosure, cable entry, pressure relief paths, and mechanical latching are equally important. Any change in barriers, vents, or internal spacing can affect the validity of the compliance claim.
The short-circuit rating depends on the installation, upstream protective devices, and the available fault current at the point of use. ATS panels are commonly designed and verified for short-circuit withstand ratings aligned with the project, such as 25 kA, 36 kA, 50 kA, 65 kA, or higher, depending on the busbar system and switching devices. IEC 61439 requires the assembly to be verified for its declared short-circuit performance, while IEC 61641 evaluates arc fault behavior under specific test conditions. The two ratings are related but not identical. The engineering team must coordinate the upstream ACB or MCCB settings, busbar sizing, and enclosure robustness to ensure both ratings remain valid.
Yes. IEC 61641 compliance is highly configuration-sensitive. Changes to enclosure dimensions, ventilation slots, door hardware, cable entry positions, internal barriers, busbar support spacing, or major switching components can invalidate the original test evidence. Even a seemingly minor modification may alter arc gas flow or pressure containment. For this reason, panel builders should maintain strict configuration control and document every approved variant. Re-verification or re-testing may be required if the change affects the tested arc-resistant behavior. This is why certification-ready ATS panels should always be built from a controlled bill of materials and detailed mechanical drawings tied to the validated design.
IEC 61641-compliant ATS panels are commonly specified in facilities where source transfer reliability and operator safety are critical. Typical applications include hospitals, data centers, airports, water treatment plants, industrial process facilities, power plants, tunnels, and large commercial buildings with standby generation. These sites often require uninterrupted transfer between utility and generator sources, and the consequences of an internal arc fault can be severe. An arc-resistant ATS panel helps reduce personnel exposure during maintenance and switching events while supporting continuity of service. In many projects, the ATS is integrated with protection relays, generator controls, and building management systems, making compliance and documentation especially important for EPC contractors and facility managers.

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