Switchgear Insulation Parts: Types, Materials, and How to Specify Them Correctly

Every switchgear panel is, at its core, a carefully engineered arrangement of insulation. The circuit breakers, busbars, and contacts get most of the attention, but it’s the switchgear insulation parts — bushings, insulators, partitions, spouts, and support components — that actually keep live conductors safely separated from earthed metalwork and from each other. A failure in any one of these parts rarely stays isolated; it tends to escalate into flashover, internal arcing, or unplanned outages.

This guide walks through the main types of switchgear insulation parts, the materials used to make them, the standards they’re tested against, and what to check before specifying them for a new panel or a replacement order.

What Counts as a Switchgear Insulation Part?

“Switchgear insulation parts” is a broad category that covers any component whose primary function is to maintain dielectric separation inside or around a switchgear panel. In practice, this includes:

• Bushings — through-wall or through-panel insulators that let a conductor pass between compartments or to the outside of an enclosure
• Support and post insulators — hold busbars and contacts in fixed position while maintaining clearance to earthed metal
• Spouts and shutters — insulating interfaces used at cable and busbar connection points, particularly in ring main units (RMUs)
• Partitions — internal barriers (metallic or insulated) separating compartments to limit fault propagation
• Vacuum interrupter housings — the insulating envelope surrounding the vacuum interrupter inside a circuit breaker pole
• Epoxy resin poles and embedded-pole assemblies — combine the conductor, contacts, and insulation into a single cast unit

Each of these parts has to satisfy the same basic requirements: hold off the rated voltage and impulse withstand level, resist surface tracking and contamination, and survive decades of thermal cycling without cracking or degrading.

Common Materials Used in Switchgear Insulation Parts

Epoxy Resin

Cast or APG-molded epoxy resin, typically filled with quartz sand or silica, is now the dominant material for solid-insulated switchgear parts, bushings, and embedded poles. It offers strong mechanical resistance, no oil or gas handling, and consistent quality when produced through automatic pressure gelation.

SF6 and SF6-Free Gas

Gas-insulated switchgear (GIS) uses SF6 or, increasingly, alternative gases and dry air as the insulating medium between live parts and the enclosure. Regulatory pressure on SF6’s high global warming potential has accelerated adoption of SF6-free designs using vacuum interruption combined with solid or dry-air insulation.

Porcelain and Composite Insulators

Still common for outdoor post insulators and older-generation equipment, porcelain and composite (silicone rubber over fiberglass) insulators remain relevant for higher-voltage outdoor applications, though epoxy has largely displaced them in indoor medium-voltage panels.

Standards Governing Switchgear Insulation Parts

Insulation parts used inside AC metal-enclosed switchgear are generally covered under IEC 62271-200 for medium-voltage equipment rated above 1 kV up to 52 kV, alongside the general switchgear requirements in IEC 62271-1. For gas-insulated switchgear above 52 kV, IEC 62271-203 sets out the dielectric, temperature-rise, and internal-arc classification requirements that individual insulation components must support as part of the complete assembly. A good technical overview of what IEC 62271-200 actually requires — including partition class, insulating medium, and internal arc classification — is available from Electrical Engineering Portal, and a more detailed breakdown of the 2021 edition’s testing changes is covered in this IEC 62271-200 guide.

Key tests relevant to insulation parts specifically include:

• Power-frequency and lightning impulse withstand voltage
• Partial discharge measurement
• Internal arc classification (IAC) testing at the panel level
• Temperature-rise testing under rated current

epoxy-resin-insulation-parts-and-bushings-used-in-medium-voltage-switchgear-panels

How to Specify Switchgear Insulation Parts

When ordering insulation parts — whether as spares, replacements, or part of a new panel build — confirm the following with your supplier:

1. Rated voltage and BIL matching the system’s insulation coordination requirements
2. Insulating medium compatibility — solid insulation, SF6, SF6-free gas, or dry air, matched to the rest of the panel
3. Partition and compartment class as required by the site’s loss-of-service-continuity and safety requirements
4. Creepage distance appropriate to the installation’s pollution severity level
5. Mechanical interface dimensions — flange size, bolt pattern, and clearance to adjacent components
6. Test certification — request IEC 62271-200/-203 and, where applicable, IEC 60137 bushing test reports for the specific batch being supplied

Mismatched insulation parts are one of the most common causes of unplanned switchgear downtime — a bushing or spout that doesn’t match the panel’s original creepage and clearance design can undermine the entire assembly’s insulation coordination, even if every other component is correctly rated.

Degatech’s Approach to Switchgear Insulation Parts

Degatech manufactures insulation components as an integrated part of our switchgear platform rather than as generic aftermarket parts. Our switchgear products range includes solid insulated panels built around epoxy resin components, and our work on SF6-free switchgear relies on the same insulation engineering discipline — matching vacuum interruption with solid or dry-air insulation systems designed for long-term dielectric stability.

Because insulation performance is only as good as the weakest component in the assembly, we also produce the vacuum interrupters and epoxy bushings that go into our panels in-house, which keeps materials, tolerances, and test data consistent across a complete switchgear order rather than relying on mixed third-party sourcing. Established in 2007 and based in Zhejiang with port access through Ningbo and Shanghai, our team supports both new-build and retrofit insulation part orders for utility, industrial, and EPC customers worldwide — more on our background is available on our company profile page.

Frequently Asked Questions

What are the most common switchgear insulation parts that fail? Bushings, spouts, and post insulators are the most commonly replaced insulation parts, usually due to surface tracking, contamination buildup, or mechanical damage rather than bulk material failure.

Can I mix insulation parts from different manufacturers in the same panel? It’s not recommended. Insulation coordination is designed at the panel level, and mixing components with different creepage, clearance, or material properties can compromise the original type-test basis for the assembly.

Are SF6-free insulation parts as reliable as SF6-based ones? Modern SF6-free designs using vacuum interruption with solid or dry-air insulation are now tested to the same IEC 62271 requirements as SF6 equipment and are increasingly specified for new projects, particularly where environmental regulations restrict SF6 use.

How often should switchgear insulation parts be inspected? Routine visual inspection is typically recommended during scheduled maintenance intervals, with more frequent checks in high-pollution, coastal, or high-humidity environments.

Need switchgear insulation parts matched to an existing panel or a new build? Contact Degatech with your voltage class, panel type, and insulating medium for a technical quotation.