Two standard families appear in low-voltage assembly documentation: IEC 61439, used widely in international project specifications, and GB/T 7251, the Chinese national standard family used as the test basis in many Chinese type-test reports. They are arranged in corresponding parts, so a report written against one can be read against a specification written in the other — provided the part numbers and edition years are checked.
How the families line up
Both families start with a general-rules part that defines terms, construction requirements and the verification items. Later parts cover particular kinds of assembly. GB/T 7251.3-2017 is the Chinese part that corresponds to IEC 61439-3, the part dealing with distribution boards intended to be operated by ordinary persons. When a report names GB/T 7251.3-2017 as its test basis, that is the line to record in the project file.
A practical habit is to write down the family and the part number, not the family alone. “IEC 61439” and “GB/T 7251” on their own leave open which part applies, and the part is what determines the verification items for the assembly in question.
Design verification in IEC 61439
IEC 61439 expresses the checking of an assembly as design verification. The general-rules part lists the characteristics to be verified — temperature rise, dielectric properties, short-circuit withstand strength, the protective circuit, clearances and creepage distances, mechanical operation, degree of protection, and others — and allows verification by test, by calculation, or by comparison with a tested reference design.
For a buyer this is useful because the documentation for an assembly may include a type-test report for a reference configuration together with design-verification records for the derived configuration. Asking which of the two covers the configuration being offered keeps the submittal tidy.
What to put in the enquiry
- Name the standard family, the part and the edition year required by the project.
- State whether the project file expects IEC wording, GB/T wording, or both.
- Ask which verification items cover the configuration being offered, and in which document each one appears.
- Keep the report’s test-basis page with the drawing, so the model, ratings and standard edition can be matched line by line.
Two details that are easy to miss
Edition years. Edition years differ between the two families and between revisions of the same part. The year printed on the test-basis page is the one that governs the report’s findings.
Ratings belong to a tested configuration. A change in busbar current, short-circuit withstand level or enclosure arrangement is a design question, and the documentation for the resulting configuration is the one to ask about.
Related reading: how to read a type-test report.
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