Overview
EN 27931:1992 (identical to ISO 7931:1985) specifies dimensions and requirements for insulation caps and bushes used in the secondary circuit of resistance welding equipment. The standard targets components used particularly with electrode back-ups, defining material guidance, surface finish, marking and designation so components are interchangeable, safe and fit for purpose in resistance welding assemblies.
Key topics and technical requirements
- Scope and purpose
- Applies to insulated taps (caps) and insulated bushes in the secondary circuit of resistance welding equipment, especially for use in back-ups as per ISO 5827.
- Dimensions
- Provides drawings and dimensional requirements for insulation caps (designated “C”) and insulation bushes (designated “B”). Dimensions are given in millimetres in the standard.
- Materials
- Recommends high‑strength insulating materials, for example glass-fibre reinforced polyamide, for both caps and bushes. Washers are specified as steel (e.g., Fe 510) when required.
- Finish
- Edges must be chamfered and grooves rounded to avoid stress concentrations and to ensure reliable assembly and insulation performance.
- Marking and designation
- Insulation caps are marked with the letter C; insulation bushes are marked with B plus the size (e.g., B 10).
- Example designation formats:
- Loading and support
- Insulation bushes are intended to be loaded only with the torque of fixing screws. Additional mechanical loads must be taken up by other measures (e.g., shoulders or supporting features); washers may be necessary where hole diameters exceed bush diameters or when slotted holes are used.
Applications and users
- Practical uses:
- Component specification for manufacturers of resistance welding equipment, electrode holders and back-ups.
- Design and procurement of insulated components for secondary circuits to ensure safe electrical isolation and mechanical fit.
- Quality assurance and compliance checks during production, assembly and maintenance of welding machines.
- Typical users:
- Welding equipment designers and OEMs
- Component suppliers and molders (plastics/insulators)
- Procurement and standards compliance engineers
- Maintenance and service technicians for welding installations
Related standards
This standard ensures compatible, safe insulation components for the secondary circuits of resistance welding systems, improving interchangeability and reducing assembly or safety issues related to inadequate insulating caps and bushes.