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Epoxy Support Insulators

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An epoxy support insulator holds a live conductor away from earth while carrying mechanical load at the same time. It keeps the energised parts of the equipment physically separated from the structure around them — which is what protects the installation, the people near it, and the continuity of service.

Indisol casts support and post insulators in epoxy resin, engineered to each application rather than picked from a catalogue: low, medium, high and very high voltage, indoors, outdoors, or in special environments such as SF6 and other dielectric fluids.

Because the part is cast rather than fired or machined, the geometry is yours to choose. Ribs, creepage profiles, mounting features and fixing centres are moulded in one piece, and threaded inserts or electrodes are encapsulated inside the resin instead of bolted on afterwards — no fasteners sitting in the insulating path.

Mechanical specification follows the duty: traction, bending or torsion. Mounting lashings follow the relevant standard or your own interface.

Looking for a different epoxy insulator? Bushings, GIS parts, dividers, sensors, third rail and custom housings are all cast here too — the guide below points you to the right one.

Range of cast epoxy support insulators, Indisol

Low voltage epoxy support insulators with threaded inserts, Indisol

Medium voltage epoxy post insulators, Indisol

Cast epoxy support and post insulators

20–40 kV/mmBreakdown strength of cast epoxy

LV to VHVVoltage classes we cast for

200 kVIn-house test ceiling

2 000 tEpoxy processed per year

Which epoxy insulator do you need?

“Epoxy insulator” is a family name, not a part number. A support insulator is one member of it. If the part you are specifying does something else, go straight to the right family.

Support & post insulatorsHold a conductor away from earth and carry the mechanical load.You are here

Medium voltage cast epoxy bushing, Indisol

BushingsTake a live conductor through a wall, an enclosure or a tank.See the range →

Cast epoxy components for gas insulated switchgear, Indisol

GIS productsBusbar supports, fuse tubes and breaker chambers inside gas insulated equipment.See the range →

Divider insulatorsInsulate and, at the same time, give a low voltage signal that follows the conductor.See the range →

Medium voltage voltage sensors and indicators in cast epoxy, Indisol

Medium voltage sensorsMeasure voltage or current to a stated accuracy class.See the range →

Third rail insulator supporting a T-section conductor rail, Indisol cast epoxy

Third rail insulatorsHold the conductor rail that powers a metro or light-rail line.See the range →

Customized cast epoxy product for medium and high voltage, Indisol

Custom HV/MV productsEpoxy housings for switches, and shapes none of the above describes.See the range →

Indoors or outdoors: the resin decides

This is the first thing we will ask you, and it is settled by where the insulator lives rather than by the voltage. Both families cover low, medium, high and very high voltage.

IndoorsAromatic epoxyBisphenol A-epichlorohydrin resin with an anhydride hardener. Excellent dielectric performance where the surface is protected from weather.

OutdoorsCycloaliphatic epoxyFilled with pre-treated silica. Resists UV, tracking and weathering without the surface degradation that limits general-purpose resins. Also the choice indoors where there is humidity or pollution.

Polluted or coastalCycloaliphatic, overmouldedThe same resin with a silicone layer overmoulded on our own line, adding surface protection where the environment is aggressive.

Where neither standard family suits the duty, resin systems can be developed to specific electrical, thermal and mechanical requirements. More on our epoxy resin technology.

How a support insulator is made

Most of what can go wrong electrically goes wrong during casting, which is why the process matters more than the datasheet.

01PrepareResin degassed under vacuum, so the mix reaches the mould without entrained air — the voids that would later become partial discharge sites.

02CastGelation under pressure at temperature for series work; vacuum or atmospheric casting for prototypes and small runs.

03FinishMetallization and sand blasting in our own factory, so the electrode and creepage surfaces stay under our control.

04ProveElectrical and mechanical testing in house and in external laboratories, under ISO 9001 and ISO 14001.

Specified to your duty, then tested

Cast epoxy has a breakdown strength of 20 to 40 kV/mm depending on the system. That is a material figure: it tells you the resin has a large margin, not the withstand voltage of a finished insulator. That also depends on the creepage path along the surface, the clearances through air and the field distribution around any embedded metal — so we dimension the part to your system voltage rather than calculating it from the material alone.

Mechanically, a support insulator usually carries load as well as voltage. Tell us the load and its direction — traction, compression, bending or torsion — and any deflection limit, and the section and fixings are designed to it. Mounting lashings follow the relevant standard or your own interface.

For gas insulated applications, where the electrical stress is highest, every single piece is tested rather than a sample: industrial frequency, partial discharges and X-ray examination of the casting.

ElectricalIndustrial frequency to 200 kVPartial discharges to 200 kVHigh voltage and current metrologyContact resistance

MechanicalFlexionTractionCompressionTwistImpactRoughness

Common questions

Can you work from our drawing?Yes. Every part we cast is engineered to the customer’s specification rather than picked from a fixed catalogue, so a drawing or a sketch of the interfaces is the most useful thing you can send.

Can metal parts be cast into the insulator?Yes — threaded inserts, electrodes and conductors are encapsulated in the resin, giving a monolithic part instead of an assembly.

Is a support insulator the same as a post insulator?In practice the terms are used interchangeably, and both describe the same job: separating conductors at different potentials while carrying mechanical load. You will also see them called standoffs.

Epoxy or porcelain?Porcelain remains a sound choice in many installations. Cast epoxy wins where you need a shape porcelain cannot easily give, where metal has to be encapsulated, or where weight and brittleness are a problem. We wrote a longer comparison of the two.

What voltages do you cover?Low, medium, high and very high voltage, in both resin families. Our in-house test capability reaches 200 kV for industrial frequency and partial discharges.

How big can the part be?From pieces above 50 kg and one metre down to small, intricate components, on 29 clamping machines and a continuous mixing line.

Send us the duty. We will design the insulator to it.

Every part we cast is engineered to a specification rather than selected from a catalogue, so you will get a design proposal back, not a page number. You do not need all of the detail to start.

Request a quotation → or see how we cast them

Useful to includeThe system voltage, and whether the insulator sits indoors, outdoors or in gasThe mechanical duty — load, direction, and any deflection limitFixing centres and interfaces, or a drawing if you have oneService temperature, and anything unusual about the environmentQuantity, and whether this is a prototype or a series