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A20 Bus Insulators

A30 Bus Insulators

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PII20A

PII20A

  • for indoor service
  • 20A strength class
  • up to 46kV/250kV BIL
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PII30A

PII30A

  • for indoor service
  • 30A strength class
  • up to 46kV/250kV BIL
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POI20A

POI20A

  • for outdoor service
  • 20A strength class
  • up to 46kV/250kV BIL
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POI30A

POI30A

  • for outdoor service
  • 30A strength class
  • up to 46kV/250kV BIL
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PII50B

PII50B

  • for indoor service
  • 50B strength class
  • 15kV/95kV BIL
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PIICR

PIICR

  • for indoor service
  • up to 15kV/95kV BIL
  • reduced diameter design
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PIICS

PIICS

  • for indoor service
  • up to 28kV/150kV BIL
  • reduced diameter design
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PIID

PIID

  • for indoor service
  • up to 5kV/60kV BIL
  • single insert per face
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PIIF

PIIF

  • for indoor service
  • up to 5kV/60kV BIL
  • unique tapered design
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PIIT

PIIT

  • for indoor service
  • up to 15kV/95kV BIL
  • single insert per face
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PIIX

PIIX

  • for indoor service
  • up to 5kV/60kV BIL
  • high cantilever applications
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POICV

POICV

  • for outdoor service
  • 2.4kV/45kV BIL
  • pin-style insulator
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What is an Epoxy Stand-off Insulator?

Epoxy stand-off (also called bus support) insulators are used as mechanical supports that provide the necessary electrical clearances for conductors and other current carrying components. They can be used in a variety of indoor and outdoor applications such as in switchgear bus supports, transformers, station posts, and other special power apparatus. The design and testing of stand-off insulators should comply with the electrical and mechanical industry standards, including ANSI, IEEE, IEC, and NEMA.

When selecting insulators for a project, there are several important design requirements to consider:

  • Application, where and how the insulator is being used and installed including environmental factors such as pollution, ambient temperature, and UV exposure.
  • Voltage class
  • Mechanical strength requirements
  • With stand-off insulators primary function being mechanical support, major consideration must be given to mechanical ratings such as:

    • Cantilever strength - the amount of weight a wall mounted insulator will support when something is hung on it.
    • Tensile strength - the amount of stress that an insulator will withstand when pressure is applied pulling straight up on the bolt in the insert.
    • Torsion strength - the amount of stress that an insulator will withstand when twisted by an applied torque.
    • Compression strength - the amount of weight an insulator will support with a direct vertical application of pressure.

    The most common class of insulators are A20 and A30 (which describes mechanical strength). Depending on project requirements, Polycast also offers insulators in other mechanical strength classes.

  • Mounting configuration
  • Epoxy standoff insulators have integrally cast threaded metal inserts for mounting onto cabinets or walls. To accommodate a wide variety of applications, thread sizes, mounting configurations, and the metal material used varies.

  • Dimensional control of height and creep
    • An insulators height determines the distance that will separate a source of voltage from ground or other components.
    • Creep (leakage) distance is the shortest distance on the surface of insulator between two conductive parts. Creep occurs when contamination builds up on the surface of an insulator and provides a conductive path for current to flow. It can be controlled by the design of an insulator’s sheds and shape, for instance, a deep shed design offers more generous creep distances.

  • Material used
  • Depending on application requirements, various types of insulating materials can be used, such as epoxy resins, glass, and porcelain. Epoxy has advantages over other materials because:

    • Epoxy insulators offer a high tolerance to physical impact and will not shatter when subjected to thermal or mechanical forces. They also offer a very high electrical breakdown strength.
    • Epoxy is homogeneous. If the surface is damaged, material underneath provides the same properties.
    • Epoxy is economical even for low production volumes


Polycast offers a wide range of indoor and outdoor epoxy stand-off insulators rated up to 46kV/250kV BIL for various strength classes. All insulators are designed and manufactured to meet and exceed North American and International standards.

Operating temperatures for indoor bis-a epoxy insulators are between -25°C to +95°C. Outdoor cycloaliphatic epoxy insulators can withstand temperatures from -50°C to +95°C and are recommended for applications where UV, pollution, or condensation are considered factors. Our materials are UL 94 V0 certified.

The Polycast engineering team welcomes the opportunity to develop new insulating devices for your unique requirements. Our in-house, adaptable manufacturing processes allow us to react quickly to customer requirements and rush requests including designs and tooling fabrication for new insulators.