Rating Plate Markings: The Smallest Page of the Safety File

The marking clause of IEC 61010 lists what must appear on the equipment and what may appear only in the instructions. The list is short, and each item is a claim: the manufacturer is asserting a supply range, a pollution degree, a measurement category, and an environmental rating, and each of those assertions has consequences in the test plan.

The mandatory items

Manufacturer identification, model or type reference, rated supply voltage or range and frequency or nature of supply, rated input power or current, and the symbols for the relevant safety classes. Where the equipment is rated for a measurement category, the category and its voltage appear next to the relevant terminal, not only in the manual.

Symbols that carry weight

The measurement category symbol, the protective earth symbol, the double insulation square, and the warning triangle each invoke a specific requirement. Printing a category symbol on a terminal that was never tested at that category is the most serious kind of marking error, because it converts an honest limitation into an instruction to the user to do something unsafe.

Durability

Markings must remain legible for the life of the equipment under the cleaning and use the instructions permit. A label that dissolves in alcohol when the manual says the case may be wiped with alcohol is a non-conformance that is easy to test and easy to overlook.

Related technical notes

• Measurement Category Symbols: What CAT II and CAT III Really Promise
• Instruction Manual Requirements: The Clauses Test Houses Read First
• A Certified Component Does Not Make a Certified Instrument