Cable accessories · 2 min read
Separable connectors for 11 to 33 kV: elbow, T-connector and the bushing interface
UD Fomra Group ·
Separable connectors join a screened polymeric cable to a ring main unit, transformer or switchgear bushing without an air-insulated termination. They are pre-moulded, touch-safe and compact, but they only fit one bushing interface. Most ordering mistakes start with choosing the connector from the cable alone.
Start from the equipment bushing
The connector has to mate with the bushing already fitted to the equipment. European standards define these bushings: EN 50180 for liquid-filled transformers and EN 50181 for other equipment, covering voltages above 1 kV up to 52 kV and currents from 250 A upwards.
Each bushing size is known by an interface letter. Manufacturers' ranges show interface A at 250 A, interface B at 400 A and interface C at 630 A, with 1250 A connectors for interface C bushings in some ranges. Read the interface from the equipment drawing or rating plate before anything else.
Elbow or T-connector
Elbow connectors are common on the smaller interfaces, typically 250 A and 400 A, where one cable lands on each bushing.
T-connectors are used on 630 A interface C bushings. Their rear opening can take an insulating plug, a coupling connector for a second cable on the same phase, or a surge arrester designed for that connector, which is why T-connectors suit RMUs and transformer feeders that need parallel cables or arrester protection.
Match the cable as well as the bushing
Within one interface, the connector body is sized to the cable: conductor size and material, and the diameter over the insulation, which must fall inside the connector's stated range. A 35 to 300 mm² range on a datasheet still depends on the insulation diameter of the actual cable.
Screen construction matters too, because the connector kit has to earth the copper wire or tape screen.
What to send for a quotation
A complete enquiry lets the principal confirm the right part numbers the first time.
- Equipment make and model, and the bushing interface (A, B, C or other)
- System voltage Uo/U (Um), for example 19/33 (36) kV
- Cable conductor size and material, insulation diameter and screen type
- Cables per phase, and whether coupling connectors or surge arresters are needed
- Indoor or outdoor, and any test point or earthing requirements
- Quantity and delivery location