TERMINALS AND TERMINAL BOARDS FOR CABLE
Power Cable Termination and Terminal Boards Assembling Procedure
Terminal Assemblies should be of the unit form suitable for mounting on a standard assembly rail, to give the required number of ways. The units should be spring retained on the assembly fail. Each individual terminal block should have independent terminals and outgoing cabling.
It should be possible to replace any unit in an assembly without dismantling adjacent units. Molding should be mechanically robust and withstand the maximum possible operating temperatures and torque which may be applied to terminal screw. All live parts should be recessed in the molding to prevent accidental contact.
Terminals should be of the screw clamp type for lower current rating which compresses the conductor or termination between two plates by means of a captive terminal screw. Contact pressure of screw clamp terminations should be independent of each other. For higher current ratings bolted type terminals are permitted. Current carrying parts should be non-ferrous and plated.
Terminal Testing Facilities
All terminals for ‘incoming’ cabling should have testing facilities, which permit the examination of the state of the circuit without disconnecting the associated cabling. Terminal blocks for current transformer secondary should be fitted with shorting/disconnect facilities.
Terminal Isolating Facilities
Terminal blocks for voltage transformers secondary should be isolatable. Terminal blocks in telemetry marshalling cubicles should be isolatable. The means of isolation should be fixed and give visual identification of the status of the terminal.
Not more than 1 wire should be connected to each terminal and cross-connection facilities should be provided where numerous cores are connected together.
Each terminal block, and every individual terminal should be identified. The terminal identification number should be included on associated schematic and wiring diagrams.
The mounting rail may only be used to provide an earth connection, when firmly bonded to the earth bar and to be approved by the Employer.
Termination Work Procedure
The Contractor should submit samples of the terminal blocks/mounting rail assemblies together with details of his proposed cabling/termination system to the Engineer for approval.
Adjacent terminals to which wires of different voltage, polarity or phase are connected should be separated by a protruding insulating barrier; this requirement also applies to terminals carrying wires of the same voltage but originating from different sources.
Wires should be grounded on the terminal boards according to their functions. Terminal blocks for connections exceeding 110V should be fitted with insulting covers.
Terminal blocks should be mounted not less than 150 mm from the gland plates, and spaced not less than 100 mm apart, on the side of the enclosure.
Terminal for Multi-core Cables
Sufficient terminals should be provided to permit all cores on multi-core cables to be terminated. Terminals for spare cores should be numbered and be located at such position as will provide the maximum length of spare core. At least 10% spare terminals should be provided in all cases.
The tails of multi-core cables should be bound and routed so that each tail may be traced without difficulty to its associated cable. All spare cores should be made off to terminals.
Recommended Terminal Block
When two lengths of screened cable are to be connected at a terminal block (i.e. junction box) a separate terminal should be provided to maintain screen continuity.
Should the terminal block manufacturer recommend that specific types of terminal tools are used (exm- parallel sided screw/drivers) the Contractor should provide three sets of these at each sub-station site. In addition the Contractor should provide 8 numbers, test leads of minimum 1500 mm length which can be inserted into the test terminals of the terminal blocks, at each sub-station. The test leads should be capable of being ‘jumpered’ together for multi-instrument use.
The use of pre-formed factory tested cable connections to field mounted marshalling boxes should be to the Engineer’s approval.