IEEE C37.20.7 Internal Arc Testing Guide for Metal-Enclosed Switchgear up to 38 kV — A Practical Overview for Engineers and Buyers

Internal arc faults are among the most severe failure events in low-voltage and medium voltage switchgear systems. They can produce extreme pressure, temperature, and mechanical stress within milliseconds, leading to equipment destruction, fire risk, and personnel injury. To address these hazards, the North American standard IEEE C37.20.7 defines a dedicated test guide for evaluating the arc-resistant performance of metal-enclosed switchgear rated up to 38 kV.

This article provides a clear, practical overview of IEEE C37.20.7 arc fault testing, its scope, classification types, test methods, and how it differs from IEC and GB standards — helping engineers, EPC contractors, and international buyers better understand arc-resistant switchgear requirements.

What Is IEEE C37.20.7?

IEEE C37.20.7-2007 (with Cor 1-2010) is the North American guide for testing metal-enclosed switchgear for internal arcing faults. It applies to:

• Medium voltage switchgear up to 38 kV
• Low voltage power switchgear
• Medium voltage motor control centers (MV MCC)
• Low voltage motor control centers (LV MCC)
• Metal-enclosed distribution equipment

The guide focuses on verifying that switchgear can contain and redirect the effects of an internal arc fault to reduce danger to personnel located near the equipment.

Typical application sectors include:

• Industrial power distribution systems
• Commercial buildings
• Utility substations
• Oil & gas facilities
• Mining operations
• Data centers
• Infrastructure projects

Difference Between IEEE and IEC / GB Arc Fault Standards

Arc fault testing standards differ significantly between North America and IEC-based regions.

IEC / GB Standards

Common IEC and Chinese GB references include:

• IEC 62271-200 / GB/T 3906 Appendix A — Internal arc classification for medium voltage switchgear
• IEC 61641 / GB/T 18859 — Internal arc test guide for low voltage assemblies

IEC internal arc testing mainly focuses on test performance criteria. If the defined acceptance indicators are satisfied — such as door integrity, indicator ignition, and enclosure containment — the equipment may pass, even if internal compartments are severely damaged.

IEEE C37.20.7 Approach

IEEE C37.20.7 places greater emphasis on structural design and compartment protection, not just pass/fail indicators. It also evaluates how arc energy affects adjacent compartments and mounted devices.

For example: If a relay or meter compartment is intended for normal operation access, an arc test in another compartment must not expose or damage that instrument area.

Functional separation between compartments is more strictly considered.

The design of pressure relief paths and venting channels is a core evaluation factor.

This makes IEEE arc-resistant certification particularly important for North American projects and multinational industrial installations.

Arc-Resistant Switchgear Types Under IEEE C37.20.7

The standard defines accessibility-based arc-resistant classifications.

Type 1 Arc-Resistant Switchgear

• Protection is provided only at the front of the equipment
• Suitable where only the front side is accessible during normal operation
• Common in wall-mounted or back-to-wall installations

Type 2 Arc-Resistant Switchgear

• Protection is provided at front, rear, and sides
• Designed for installations where multiple sides are accessible
• Preferred for walk-in electrical rooms and industrial environments
• Some manufacturers also provide enhanced sub-types (such as Type 2B) with additional compartment isolation features.