Machinery safety: Points to consider
27 April 2017
Paul Taylor, manager for machinery safety at TÜV SÜD Product Service, a global product testing and certification organisation, asks the question: 'How electrically safe is your machinery?'
The key standard for machinery electrical safety is EN 60204-1, which provides requirements and recommendations relating to the electrical equipment of machines. This includes, but is not limited to, enclosures, isolators, colour coding of actuators and documentation.
The standard requires that electrically live parts be located inside enclosures to provide protection against a human having direct contact with them. Any enclosures should only be able to be opened under one of three conditions:
- A key or tool must be used to open it.
- Before it can be opened, live parts must be automatically disconnected.
- If opening with a key or a disconnection device is not possible, opening of the enclosure should only be possible when all live parts are protected against direct contact to at least IP2X or IPXXB (see standard IEC 60529).
It is recommended that enclosure doors are no wider than 0,9m and have vertical hinges that have an opening angle of at least 95°. Any large-scale enclosures, which readily allow a person to fully enter, shall be provided with means to allow escape.
Enclosures intended for such access, for example for resetting, adjusting, or maintenance, shall have a clear width of at least 0,7m and a clear height of at least 2,1m.
In cases where equipment is likely to be live during access; and conducting parts are exposed, the clear width shall be at least 1,0m. In cases where such parts are present on both sides of the access way, the clear width shall be at least 1,5m.
An isolator switch is a manually actuated control device used to switch off the supply of electrical energy to all or a part of an installation where a risk of electric shock or another risk is involved. The requirements relating to isolators are listed in Clause 5 of EN 60204.
Clause 10 of EN 60204-1 includes colour coding and marking requirements for push-button actuators. The colour red is reserved for emergency stop and emergency switching-off actuators. It may also be used for stop/off actuators, but it is recommended that the colour red is not used near an emergency operation device.
Also, unless otherwise agreed between the machine supplier and the user (the details of which is covered in Annex B of EN 60204-1), machine status indicator lights must be colour coded, with each colour identifying a specific status.
Clause 17 of the Standard outlines the technical documentation that is required to prove compliance. This includes information relating to a machine’s electrical installation, operation, and maintenance, which can be in the form of drawings, diagrams, charts, tables, and instructions.
Whilst the Standard recognises that different levels of detail will be needed according to the complexity of the machinery, there are particular requirements no matter what the machine type. The verification process under clause 18 is intended to ensure a product meets the specified electrical safety requirements of EN 60204-1. This can be done at different stages throughout the design and development lifecycle process, or at the end of it.
The extent of the verification that is required is made clear in the specific product standard that relates to each different type of machine. However, where there is no such dedicated standard, EN 60204-1 requires that it must always include:
- Verification that the electrical equipment complies with its technical documentation
- In case of protection against indirect contact by automatic disconnection, conditions for protection by automatic disconnection shall be verified according to 18.2
- Functional tests
The complexity of EN 60204-1, coupled with the potential lethal consequences if electrical safety is incorrectly administered, means that it is not a process that machine users can afford to get wrong. However, the development of a practical checklist is a useful approach that will help ensure all relevant considerations have been covered.