QUICK ANSWER
U₀/U identifies rated voltage relationships for a cable system; a factory test voltage is a separate value and must not be treated as the operating rating.
01Read both values
U₀ generally describes the rated voltage between a conductor and earth or metallic screen, while U describes that between conductors. Use the definition in the applicable specification. A quotation that only says “medium voltage cable” is not precise enough for approval.
02Check the system information
Provide system voltage, earthing arrangement and relevant fault conditions to the designer and supplier. The cable choice and accessory ratings must suit that system. Confirm whether any stated maximum system voltage is part of the proposed specification.
03Keep test values separate
Test reports describe a specified test method and duration. Passing such a test does not authorize continuous operation at that test value. Request a clear table separating rated voltage, standard, routine tests and any project-specific acceptance tests.
Before you send an enquiry
- Provide the system diagram
- Confirm U₀/U and standard
- Match accessories
- Separate rating and test values
References & further reading
An introductory buying guide, not a project design or a claim of certification. Confirm current standards, local requirements and the exact product documentation with the designer and supplier.