IEC 60947-5-8:2020

Overview

IEC 60947-5-8:2020 is the International Electrotechnical Commission (IEC) standard that defines requirements for three-position enabling switches used in low-voltage switchgear and controlgear. Edition 2.0 (2020) replaces the 2006 edition and updates scope, operational characteristics and tests. The standard covers three-position enabling switches intended for electrical control circuits with rated voltages up to 250 V AC (50/60 Hz) or 300 V DC. It specifies construction, performance, testing and product information for switches that form part of enabling devices used to permit, prevent or stop machine operation.

Key topics and technical requirements

• Function and definition: A three-position enabling switch has three sequential actuator positions; the enabling contact is closed only in the mid position and open in the rest and fully depressed positions.
• Scope of use: Intended as components of enabling devices that, when continuously actuated, allow machine operation to be initiated by a separate start control, and when deactivated, initiate a stop and prevent restart.
• Construction & performance: Requirements for actuating systems, contact elements, number of poles, and mechanical characteristics are specified (see clauses on characteristics, construction and tests).
• Environmental & mechanical tests: Normal service, mounting and transport conditions plus tests for shock, vibration and durability are included (referenced from IEC 60068 series).
• Product information & marking: Manufacturers must provide key product information and ratings for safe integration.
• Functional safety support: Annex B (new in 2020) provides a procedure to determine reliability data for use in functional safety applications (useful for safety lifecycle and risk assessments).
• Examples: Annex A (informative) adds figures showing typical devices incorporating three-position enabling switches (grip, pendant, foot-actuated, joystick, etc.).

Applications and who should use this standard

• Machine builders and integrators designing human-operated safety controls (grip handles, push-buttons, foot pedals, teaching pendants).
• Functional safety engineers performing risk assessments and calculating reliability data for safety-related control systems.
• Switch manufacturers and designers developing three-position enabling switches and needing to meet IEC performance and testing requirements.
• Test laboratories and certification bodies verifying compliance for low-voltage control devices.
  Practical applications include assembly robots, hand-held and portable machine controls, operator pendants and any system requiring a deliberate enabling function to allow safe machine operation.

Related standards

• IEC 60947-1 (General rules for low-voltage switchgear and controlgear)
• IEC 60947-5-1 (Electromechanical control circuit devices)
• IEC 60204-1 (Safety of machinery - electrical equipment of machines)
  These documents should be used in conjunction with IEC 60947-5-8 for complete compliance and system-level safety design.

Keywords: IEC 60947-5-8, three-position enabling switches, low-voltage switchgear, enabling device, machine safety, functional safety, reliability data, enabling contact.