Avoid EMC assumptionsMany machine builders assume that if each individual electrical or electronic component in a machine carries the CE marking, then the entire machine will also meet EMC requirements. However, that is not the case, as Paul Laidler explains.
Machine builders have a legal obligation to ensure that products offered for sale in the European Union carry the CE marking. The CE marking shows compliance with the Machinery Directive and in order to comply with this particular directive, it is also necessary to show that the machine meets the requirements of all other applicable directives. For any machine that has electrical or electronic components, that includes the EMC Directive (2004/108/EC).
The EMC Directive, 2004/108/EC, is implemented by the Electromagnetic Compatibility (EMC) Regulations 2006 in the UK. The standards that underpin it set strict limits for radiated emissions, which is the amount of electrical interference that a device produces. While a single item of equipment might meet these limits, it provides no guarantee that, if you combine multiple numbers of them, the overall emission levels will still be satisfactory. This problem is neatly summed up as 'CE plus CE doesn't equal CE'.
For many machine builders, this chain of requirements could prove a complex minefield to navigate. So, how can they demonstrate compliance with the EMC Directive? The Directive specifies that they should compile technical documentation to show that basic requirements have been met and then complete a Declaration of Conformity. Nowhere in the EMC Directive does it state that testing is mandatory, but how can the EMC performance of a machine be predicted unless testing is carried out?
When asked for clarification of this issue, the Health & Safety Executive provided a written response that includes the following statement: "Section 6 of the Health & Safety at Work Act (HSW) places a duty on manufacturers to carry out or arrange for the carrying out of such testing and examination as may be necessary to ensure that the article is so designed and constructed that it will, as far as is reasonably practicable, be safe and without risks to health. In the context of EMC, in most applications it is the electromagnetic immunity of equipment that is of interest in relation to Section 6 of the HSW. If it is reasonably practicable to carry out testing for immunity to electromagnetic disturbances, the HSW requires this to be carried out."
This statement leaves no room for doubt about the necessity for EMC testing of machines in the vast majority of cases - there is simply no shortcut to achieving compliance with the EMC Regulations. Unfortunately, there is also no doubt that EMC testing can be complex and time consuming, especially for the majority of machine builders that lack in-house expertise in this specialist area.
There are many examples of what happens when this advice is ignored, such as when drivers in a Windermere shopping area found that their wireless key fobs would mysteriously cease to operate the locking mechanisms of their cars. An OFCOM (Office of Telecommunications) investigation revealed that the key fob signals were jammed by emissions from a wireless ordering system in the nearby café.
High levels of interference
While this example might seem trivial, consider what might happen if a machine was disturbed by electromagnetic interference from a nearby mobile phone or welder and started-up unexpectedly. Conversely, if the electrical and electronic systems fitted to a machine generate a high level of interference, they may cause other nearby equipment to malfunction. In fact, problems of this type have occurred and have led to serious consequences, which is why the EMC Directive was introduced.
To understand the implications of these regulations for machine builders, a good starting point is to look at the 'Guide to the Electromagnetic Compatibility (EMC) Regulations 2006', which can be downloaded free of charge from the Department for Business Innovation and Skills website - www.bis.gov.uk.
Section Two of this guide, which covers essential requirements, includes statements that can be summarised as saying that equipment must be designed and manufactured so that the electromagnetic disturbance it creates is not excessive, and so that it has a reasonable level of immunity to electromagnetic disturbances. In addition, fixed installations, which includes the majority of machines, must follow good engineering practices and respect the intended use of their components.
Another interesting statement follows: "There are no conformity assessment or CE marking requirements for fixed installations." This statement is taken directly from the guide, but does it really mean that builders of machines categorised as fixed installations have no need to concern themselves with the EMC performance of their products? Indeed it does not. Note that this same section of the guide contains the words: "the essential requirements for all equipment are set out in Regulation Four." In other words, machines that are regarded as fixed installations must still be designed and manufactured so that they meet the essential requirements - the only relaxation of the rules relates to assessment and marking, not to performance.
Those machine builders that assume all that they have to do to meet the requirements of the EMC Directive is to use components that carry CE marking are following a dangerous route, not only from a non-compliance stance, but also because of the risk of severe injuries that could be caused if a machine malfunctions. While EMC is a complex and confusing issue, taking the correct compliance measures cannot be ignored. To ensure safety the final machine must be properly tested.
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