Systems EMC procedures

Company procedures must:

Contain EMC compliance management and control procedures as described in this guide, added to and modified by company circumstances and experience, such as EMC test results and experiences of actual interference events.

Describe the EMC testing regime to be followed which will range from simple DIY tests to partial or full tests on the factory floor, at the final installation, or in an independent testing laboratory, or any mixture of these methods.

Include detailed work instructions for:

++ Assessing the operational electromagnetic environment, and deciding on the functional degradations allowed during EM disturbances and the amount of emissions (usually part of the tender submission and contract approval process)

++ Specifying the EM performance of bought-in electrical/electronic/programmable units, and those designed in-house

++ Obtaining electrical/electronic unit supplier's EMC instructions, and following them in every detail

++ Specifying ground/earth and screen termination methods

++ Specifying cable classes (and standard cable types, e.g. by manufacturers' part numbers)

++ Backplate/chassis layout rules and minimum cable spacings (by cable class)

++ Segregation of items of apparatus and other EMC protective measures

++ Providing all this information on the assembly drawings and installation manuals

++ Storing of drawings, design rationales and test results, to be able to show "due diligence" in EMC compliance up to ten years later.

Designers must:

Follow the company's procedures and work instruction for the EMC practices concerned.

Take care only to purchase units with adequate EMC performance for the intended environment and use. Obtain and check suppliers' EMC documentation. Obtain all manufacturers' instructions for EMC and follow them. If in doubt get more information and expert advice.

Communicate all the detailed assembly requirements clearly on all assembly drawings, for example...

• ++ Identify the ground/earthing and screening methods
• ++ Identify the cable classes (and the types and grades of cables to be used)
• ++ Draw backplate/chassis layout positions of major items and those critical for EMC
• ++ Specify segregation distances from other apparatus and any other protective measures required by the installation (e.g. filtering, surge protection, ground/earthing)
• ++ Show on the assembly and installation drawings the routes to be used for the different cable classes.

Remember some electrical/electronic units may have special EMC-related needs, such as: cable screens only connected at one end; or cable screens connected to other than ground/earthed chassis (e.g. connected to an insulated terminal); or special cable types (e.g. double-screened). In every such instance the assembly drawings must be clearly marked with exactly what is required using clear sketches or descriptions in words.

Assemblers must:

Follow the company's procedures and work instructions for the EMC practices concerned.

Reject all drawings which are incomplete, e.g. any with an ground/earth connection without an associated bonding method, or any with a cable class (or its route) undefined.

Follow the designers' drawings exactly, including:

• ++ Following ground/earthing and screen-terminating methods
• ++ Using the correct cable types for the different classes
• ++ Laying out the electronic and electrical units on the backplate or chassis according to the assembly drawings
• ++ Routing the segregated cable classes exactly as shown on the assembly drawings
• ++ Following any other special instructions on the assembly drawings.

Any necessary changes must be agreed with designers and shown by the final issue of the drawings. If there are any doubts about anything on the drawings, ask.

User and Installation Manuals:

These should encourage good EMC practices to be continued in the user's system or installation, including:

• ++ Identifying the cable classes for all user connections
• ++ Specifying the cables and connectors to be used (e.g. twisted pair, braid or foil, etc., manufacturers' part numbers preferred).

These should also recommend following IEC 61000-5-2:1998 or other appropriate installation EMC standard, including:

• ++ Segregating the cable classes from each other
• ++ Cable routing
• ++ Installation ground/earth bonding and meshing
• ++ Cable screen 360-degree bonding at both ends
• ++ The use of parallel ground/earth conductors ( PECs).

These manuals should also describe any special installation instructions for achieving EMC, such as those derived from an electronic unit manufacturer's special installation instructions for EMC. Manuals may also need to specify who is allowed to install (e.g. what skills, experience, or qualifications they must have). In some cases these have to be your own installation personnel.

Finally, user manuals must state that EMC compliance cannot be assured if their instructions are not followed, or if installation, commissioning, servicing or modifications are carried out by non-approved or incompetent persons. Offer assistance with queries or difficulties.

It may be useful to duplicate all the company's own drawings of ground/earthing and screening methods, and the rules for choosing and routing cable classes, so that the user is quite clear about what to do and is therefore unable to claim you didn't provide him with the necessary detailed EMC installation information.

Installation, commissioning, service

Follow the company's procedures and work instructions for the EMC practices concerned.

Reject all drawings which are incomplete, e.g. any with an ground/earth connection without an associated method, or any with a cable class (or its route) undefined.

Follow the designers' drawings and installation instructions exactly, including:

• ++ Following ground/earthing and screen-terminating methods
• ++ Using the correct cable types for the different classes
• ++ Maintaining the intended segregation between items of apparatus and their cables
• ++ Routing the segregated cable classes exactly as required
• ++ Using parallel ground/earth conductors ( PECs) of the correct type, where required
• ++ Following any special instructions on the assembly drawings and installation manuals
• ++ Not altering or modifying anything which is important for achieving EM performance.

Installation, commissioning and service staff may need to be trained in identifying and dealing with interference problems, and may need a basic kit of equipment and tools to allow them to apply remedial EMC measures during their work.

Any necessary changes must be agreed with designers and shown by the final issue of the drawings. If there are any doubts about anything on the drawings or in the installation and commissioning instructions, ask.

Next: Determining EMC performance criteria

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