Paul Laidler of Laidler Associates, part of TUV SUD Product Service, explains machine builders' obligations under the Low Voltage Directive 2006/95/EC, and what needs to be taken into account when assessing the electrical safety of machines.
"The Declaration of conformity for machinery subject to the Machinery Directive shall not refer to the Low Voltage Directive." For many machine builders, this statement may come as something of a surprise and some may even doubt whether it is correct. However it is a direct quote from the Guide to Application of the Machinery Directive 2006/42/EC published by the European Commission, a copy of which can be downloaded free of charge from the European Commission website.
But can this statement be taken to mean that machine builders do not have to concern themselves with the Low Voltage Directive (LVD)? Far from it! The Guide and, indeed, the Machinery Directive itself, make it clear that "the safety objectives set out in Directive 73/23/EEC shall apply to machinery." And Directive 73/23/EEC, which has recently been re-designated 2006/95/EC, is the LVD (Low Voltage Directive). So what the Machinery Directive actually says is that the machine has to conform with the requirements of the LVD, but that no declaration to this effect should be made.
Whether or not this is logical is a moot point, but the real question is how should machine builders set about ensuring that their products conform to the requirements of the LVD? Fortunately, the Guide mentioned above provides a little more advice. In Section §222, which relates to Section 1.5.1 of the Essential Health and Safety Requirements (EHSRs) of the Machinery Directive, the Guide notes "general specifications for the design of the electrical equipment of machinery are given in EN 60204-1: and specifications for high voltage electrical equipment of machinery are given in standard EN 60204-11".
It is clear from this statement that compliance with the relevant parts of EN 60204 is the key to meeting the requirements of the LVD and hence the Machinery Directive. In practice, only very specialised machines are likely to incorporate high-voltage electrical equipment, so the part of the standard of most interest is EN 60204-1, Safety of machinery. Electrical equipment of machines. General requirements. It is very important to note, however, that this may not be the only relevant electrical standard. In fact, Section 1.5.1 of the Machinery Directive ESHRs goes on to state "specifications for electrical equipment are also given in many standards for specific categories of machinery".
This means that it is the responsibility of machine builders to determine which of those product standards apply to the machines they are building, and to ensure that their equipment meets the appropriate requirements. At this point, it is worth sounding a note of caution. Many electrical engineers are used to referring to and relying on the 17th Edition of the IET Wiring Regulations (BS 7671) for guidance in their work. The IET Wiring Regulations are NOT, however, applicable to machines, so those who work on machines must look elsewhere for guidance.
Consideration of the standards for specific types of machines is beyond the scope of this short article, but it is useful to look in general terms at EN 60204-1 to give machine builders an indication of the sorts of things they need to consider in relation to the electrical design and construction of their products.
Electrical design and construction
As might be expected, the standard is very wide-ranging. Its principal sections deal with: supply conductor terminations and disconnection/isolation devices; protection against electric shock; protection of equipment; equipotential bonding; control circuit and control functions; operator interfaces and machine-mounted control devices; controlgear location, mounting and enclosures; conductors and cables; wiring practices; electric motors and associated equipment; accessories and lighting; and marking, warning signs and reference designations. The scope of the standard is not, however, limited to the equipment itself, since it also covers technical documentation and verification/testing.
From this brief overview of the scope of EN 60204-1, it can readily be seen that ensuring compliance requires considerable specialist expertise and often involves a lot of work. For these reasons, many machine builders prefer to call on support from an expert consultant, such as Laidler Associates, to assess the electrical equipment on their machines.
Using a consultant can save considerable time and money but, if those savings are to be maximised, it is a very good idea to involve the consultant at the earliest possible stage of the machine design process, as this will enable them to provide advice to ensure that potential problems are designed out rather than built in. Remedial work after a machine has been built is always more costly than getting the design right in the first place.
But what sort of things can go wrong? Surely, provided that good engineering practice is followed, it is not too difficult to ensure that the electrical equipment on a machine is standards-compliant? In fact there are a many things that are all too easy to overlook. As just a small part of their machine assessment work, Laidler's inspectors use a checklist with 45 items, all of which are based on problems that they have previously encountered.
Just a few examples form this checklist are: high- and low-voltage wiring in the same conduit; isolator easily overridden on the enclosure door; no earth strap on the enclosure door; fluid handling equipment in the same enclosure as electrical equipment; multiple connections to a single termination point; and isolators that do not meet the requirements of EN 60947-3. That is just six things out of the 45 on the list, and that list is by no means exhaustive.
It should by now be clear that machine builders do, in fact, face significant legislative requirements in relation to the electrical equipment on their machines, even if the Machinery Directive does excuse them from explicitly declaring compliance with the Low Voltage Directive. Unless they have specialist expertise in-house, therefore, they may well find that the most reliable and, ultimately, least costly route to compliance is to engage the services of a consultant with proven experience and expertise in this area. Follow the link for more information about the services Laidler Associates offers in relation to the Low Voltage Directive 2006/95/EC.