Start with the bushing and cable interface
Send the supplier the cable data sheet and a marked single-line diagram. Record conductor material and size, insulation, screen or sheath construction, number of cores, phase arrangement, operating voltage, highest voltage for equipment, fault duty, cable entry direction, termination length and any bending or support limits. State whether the cable connector is supplied by the RMU manufacturer, cable contractor or another approved accessory supplier.
| Compatibility item | What to confirm | Evidence to request |
|---|---|---|
| RMU bushing | Interface type, dimensions, contact arrangement and supported accessory family | Bushing drawing, connector list and assembly detail |
| Cable construction | Conductor, insulation, screen, sheath, diameter and core arrangement | Cable data sheet and termination selection record |
| Electrical duty | Voltage, insulation, short-circuit, earthing and test requirements | Approved specification and applicable accessory evidence |
| Mechanical fit | Phase spacing, connector depth, cover, bend radius and support | Compartment drawing with installed connector |
| Earthing and screen | Screen bonding, earth braid, test point and fault indication | Earthing diagram and terminal schedule |
| Installation and test | Sequence, torque, tools, isolation and permitted test interface | Manufacturer procedure and test record |
IEC 60502-4:2023 specifies type-test requirements for accessories for certain medium-voltage extruded-insulation cable systems. It does not pair any connector with any RMU, approve a project installation or replace the equipment manufacturer’s compatibility evidence. See the IEC 60502-4 publication.
Do not compare voltage labels alone
Two connectors can share a voltage class while differing in bushing geometry, screen arrangement, contact size, stress-control components, installation length or test access. Conversely, a cable connector family may support several cable sizes only within a stated range. Ask for the complete connector reference and the exact RMU bushing drawing.
Ask the supplier to identify the exact bushing/interface and the compatible cable-accessory arrangement. The evidence should name the offered equipment, relevant interface designation, required cable data and any restrictions. A matching shape or nominal voltage is not a complete compatibility assessment. Keep connector supply, adapters, lugs, fixing hardware and installation materials visible in the quotation, including any items supplied by the cable contractor.
Installation must follow the approved equipment and cable-accessory procedures for the actual products. Request those instructions and identify the qualified contractor responsible for the work. Do not copy dimensions, torque values or assembly methods from an unrelated catalogue. Agree which interface drawings, compatibility statements, factory records and site acceptance checks are delivered with the purchased RMU.
Show the installed connector in the compartment drawing
Ask for a drawing that shows the connector, bushing centre, cover, phase spacing, cable bend, support, screen earth and access to the test or voltage-detection interface. Include single and double-cable arrangements when relevant to the project. A connector may fit the bushing but prevent the cover from closing or leave insufficient space for the cable’s minimum bend radius.
Record the force and support path from the cable. The RMU should not carry an unplanned mechanical load from a rigid or badly supported cable. Identify gland plates, cleats, brackets, earthing braid, stress-control parts and sealing items. If the cable termination is supplied loose, list storage, installation and test responsibility separately.
The existing RMU cable compartment checklist covers the broader compartment layout. The RMU cable test and earthing guide focuses on permitted test states, while the switchgear retrofit cable-interface guide covers reuse of existing cables. This article focuses on proving connector-to-bushing compatibility before purchase. Use the Jinxing ring main unit page and project enquiry page to request an itemised interface review.
Include the acceptance and future-change boundary
State what is checked at the factory and what is checked after the cable is installed. The accepted record can include connector identity, bushing reference, installation method, tightening record, screen-earth continuity, phase identification, test access and photographs where required by the project. The applicable tests and values must come from the approved specification and manufacturer instructions.
If the cable supplier, utility or future extension may change the connector, record that as an open interface. A new connector can affect the RMU cover, cable compartment, earthing, test method and outage plan. Do not approve a substitute from a different manufacturer solely because its catalogue lists the same voltage and conductor range.
Example: replacing a cable-fed RMU
Consider a replacement RMU where the existing cable is short and its screen arrangement is not fully documented. The buyer should survey the cable, identify the installed termination, request the offered RMU bushing drawing and compare retermination, cable extension and full cable replacement. The quotation should state the connector, accessories, field work, outage, testing and exclusions. This creates a connection decision that engineering and procurement can both review.
RFQ checklist
- Cable data sheet, conductor, insulation, screen, sheath, size and core arrangement.
- RMU bushing reference, interface drawing, voltage and insulation requirements.
- Connector manufacturer and part number, accessory set and supported cable range.
- Phase spacing, depth, cover, bend radius, support, gland and earthing details.
- Test points, voltage detection, screen bonding and permitted test method.
- Factory-fitted, supplied-loose and field-installed components with owners.
- Installation sequence, tools, tightening record, safety controls and outage.
- Factory, site and cable-termination tests with accepted handover evidence.