How to Select Arc Resistant Switchgear

Arc-resistant switchgear is not a generic safety upgrade. It is a tested assembly with a defined arc containment and pressure-relief performance under specific conditions. Knowing how to select arc resistant switchgear starts with the actual hazards at your facility: available fault current, clearing time, equipment layout, access requirements, and the tasks workers perform near energized sections.

The objective is not simply to purchase gear labeled “arc resistant.” The objective is to reduce the consequences of an internal arcing fault for workers who may be near the equipment, while supporting a broader electrical safety program built around NFPA 70E principles, OSHA requirements, equipment maintenance, and sound operating procedures.

Start With the Arc Flash Risk, Not the Equipment Catalog

An arc-resistant lineup should be selected after the facility has reliable electrical system information. A current one-line diagram, utility data, transformer information, conductor lengths, protective device settings, and available fault current are foundational. Without this information, it is difficult to determine whether a proposed lineup has adequate short-circuit and arc-containment ratings for the installation.

An arc flash study provides the data needed to evaluate incident energy, arc flash boundary, and protective-device clearing time. It also identifies whether changes to protective settings, relaying, current-limiting devices, or zone-selective interlocking could reduce the energy released during a fault. Arc-resistant construction can limit worker exposure to the products of an internal arc, but it does not replace fast fault clearing.

This distinction matters. A lineup may survive an internal arc test at a stated current and duration, yet an upstream device with slow clearing characteristics can still create an unacceptable hazard profile. The best result often combines arc-resistant construction with protection improvements that shorten arcing duration.

Understand What “Arc Resistant” Is Tested to Do

For medium-voltage metal-enclosed switchgear, arc-resistant performance is generally evaluated under IEEE C37.20.7. The standard defines test approaches and accessibility classifications that describe which sides of the equipment are intended to provide personnel protection during a qualified internal arcing event.

Arc-resistant equipment is designed to direct hot gases, pressure, and other fault byproducts away from designated accessible areas. That may involve reinforced doors and compartments, pressure-relief flaps, plenum systems, exhaust ducts, arc-resistant control compartments, and mechanical interlocks. The exact design varies by manufacturer and lineup.

It does not mean the equipment is harmless during an arc flash. The event can still damage equipment severely, interrupt operations, create fire and smoke hazards, and require extensive recovery. It also does not eliminate shock hazards, the need for proper boundaries, or the expectation that energized work be justified, planned, and controlled.

Select the Right Accessibility Type

A central decision is the accessibility type required for the location and work practices. In simplified terms, the equipment’s tested protection may apply to the front only, the front and sides, or the front, sides, and rear. The required type depends on where people can be during normal operation, inspection, maintenance, and emergency response.

A front-accessible lineup installed against a wall may be appropriate when the rear cannot be accessed and side exposure is controlled. That same lineup may be a poor choice in a room where personnel routinely pass beside the equipment or where rear access is needed for cable termination, maintenance, or troubleshooting.

Do not treat room clearances as a minor installation detail. Required working space, egress routes, equipment access, and arc exhaust paths must all be coordinated. If the switchgear releases pressure through the top or rear, the building structure, ducts, ceiling, adjacent equipment, and personnel pathways must support that design.

Match Ratings to the Actual Electrical System

The nameplate ratings must fit the electrical system, not merely meet the existing switchgear’s nominal voltage. Verify the following before finalizing a specification:

• System voltage, insulation class, and grounding method.

• Available short-circuit current at the switchgear bus.

• Arc test current and duration, including the protective device clearing time used for the application.

• Continuous bus rating, feeder loading, and future load growth.

• Main bus, feeder, and breaker interrupting and momentary withstand ratings.

• Environmental conditions, including indoor or outdoor use, altitude, contamination, temperature, moisture, and corrosive exposure.

The arc test current and duration deserve particular attention. A manufacturer’s arc-resistant classification is valid only within its tested conditions and configuration. A lineup tested for a lower fault level or shorter duration should not be assumed suitable for a system with higher available energy or slower protection.

Future expansion also deserves a deliberate decision. Over-specifying every section can waste capital, but installing a lineup with no capacity for foreseeable load, feeder, or protection changes can create a costly replacement project later. Document the load forecast and expansion assumptions instead of relying on generic contingency margins.

Evaluate the Entire Lineup Configuration

Arc-resistant performance is often configuration-dependent. A switchgear lineup may require specific doors closed, covers installed, compartments latched, pressure-relief paths connected, and cable compartment arrangements maintained to achieve its classification. Some designs also require particular installation clearances or an exhaust plenum arrangement.

Ask the manufacturer or supplier to identify exactly what is included in the tested assembly. This should cover incoming sections, main breakers, tie breakers, feeder compartments, low-voltage control compartments, cable termination sections, metering, auxiliary compartments, and any transition to other equipment. A weak point at a tie section, cable compartment, or field-added enclosure can undermine the intended protection strategy.

The same scrutiny applies to aftermarket changes. New conduit penetrations, control wiring modifications, replacement doors, ventilation changes, or field-installed accessories can affect pressure containment and exhaust routing. Require a documented review before modifying an arc-resistant lineup.

Consider Operating and Maintenance Practices

Switchgear selection should reflect how the equipment will actually be used. If operators must rack breakers, reset protective devices, perform switching, or access controls while energized, specify features that reduce exposure during those tasks. Depending on the system, this may include remote racking, remote switching, remote relay access, viewing windows, infrared inspection provisions, or isolated low-voltage control compartments.

These features are not substitutes for an energized work permit process or established approach boundaries. They are engineered controls that can reduce the need for workers to stand in a high-energy area during routine actions.

Maintainability also affects safety. Select equipment that supports practical inspection, testing, cleaning, and repair. If accessing a component requires excessive disassembly or puts technicians in difficult positions, preventive maintenance is more likely to be deferred. Protective relays, breakers, shutters, interlocks, and arc-detection components must remain serviceable over the equipment’s life.

Coordinate Arc Detection and Fast Clearing

For higher-energy systems, arc flash detection can be a significant part of the mitigation strategy. Optical sensors, overcurrent elements, differential protection, and high-speed tripping schemes can detect an internal arc and initiate fault clearing faster than conventional protection alone.

The benefit depends on coordination. A detection system must be engineered around zone coverage, trip logic, breaker operating time, control power reliability, fail-safe behavior, and interactions with upstream and downstream protective devices. Poorly designed logic can create unwanted trips or fail to provide the expected reduction in arcing duration.

When evaluating options, compare the total risk-reduction approach: arc-resistant construction, relay settings, detection speed, breaker performance, remote operation, maintenance condition, and worker task exposure. There is no single product feature that solves every arc flash problem.

Specify Installation, Documentation, and Acceptance Requirements

A sound purchase specification should require more than equipment ratings. Include submittal requirements for certified drawings, one-line diagrams, protective-device data, arc-resistant test classification, pressure-relief details, installation instructions, and maintenance documentation. Require the manufacturer to identify restrictions that affect the tested arc-resistant configuration.

Before energization, verify that the installed lineup matches the approved design. Confirm breaker settings, relay logic, control wiring, exhaust plenums, enclosure closures, labels, grounding, and interlocks. Update the arc flash study when the new equipment or protective settings change the system results, then apply field labels and train affected employees on the revised hazards and procedures.

For many facilities, replacement must occur in phases. Start with switchgear where incident energy is high, workers routinely operate equipment energized, fault clearing is slow, or the equipment condition is deteriorating. ZMAC Electrical Safety can help connect the study data, remediation priorities, equipment options, labels, and program requirements so the project moves from analysis to field implementation.

Arc-resistant switchgear is most effective when it is selected as part of a disciplined risk-reduction plan. Build the decision around verified system data, tested equipment limits, the spaces workers can access, and the operating practices your facility must support. That approach protects workers without creating false confidence in a label or a single equipment feature.