MEW SPECS

The use of armoured cables shall only be permitted subject to the Owner’s/Engineer’s approval. Where applicable cable armouring shall not be used as a protective screen. Equipment shall be designed so that the armouring of all incoming and outgoing cable can be connected together externally, but shall be electrically isolated from the enclosure. The cable armour shall be connected to the site earth at a single point. Cubicles, desks etc, shall be equipped with a “clean” instrument earth comprising an insulated copper earth bar for the connection of cable screens. All “clean” instrument earth bars shall be clearly labelled as such. Connection of the instrument earth to the site earth shall be by separate conductor to the equipment safety earth. Where the system design requires a single connection from the control and instrumentation equipment to the main plant earth bus, then a removable link shall be provided to connect the equipment earth to the main plant earth bus for testing purposes. This removable link shall be clearly labelled with a warning indication. All non-current carrying metallic parts of plant, equipment, components, enclosures, racks etc, shall be earthed by connection to the main plant earth bar in an approved manner and all earthing terminals and connections shall be of adequate dimensions. For all panel, cubicle doors or swinging frames, flexible cable or braid shall be used for earthing these items; the door hinges shall not be accepted as a means of earthing this part of the equipment. Except where otherwise approved, a stud type terminal of diameter not less than 12 mm or a tapped boss of equivalent size shall be provided on the outside of each cabinet or structure for the purpose of making the connection to a convenient local earth point. The design of equipment shall be such that cable screens and cable armouring are kept electrically separate throughout the equipment installation so as to avoid the introduction of earth loops and minimize interference pickup.

5I.2.14.5

Cabling

All cabling and wiring shall be of the flame-retardant and fire resistant accordance with BS 5467, BS 5308 and meet the requirements of 5E.

type in

Field multicore cables shall have stranded copper conductors of 1.0 mm2 minimum cross sectional area, thermoplastic insulation and an overall thermoplastic sheath. These cables shall have an overall metallic shield. Cables shall be selected from the following range of cores 4, 7, 12, 19, 27 or 37 cores. There shall be a minimum of 20% spare cores, but no less than two cores, for future use.

Specification No. MEW/SOCGT Issued via Addendum No-1, July 2012

5I–103

Contractor’s Initial and Stamp

Field multipair cables shall have twisted pairs of stranded copper conductors of 1 mm2 minimum cross sectional area, thermoplastic insulation and an overall thermoplastic sheath. These cables shall have an individual insulated metallic shield applied to each pair and an overall metallic shield. Cables shall be selected from the following range of pairs 2p, 5p, 10p, 20p or 50p. There shall be a minimum of 20% spare pairs, but no less than 1 pair, for future use. Optical fibre cables shall have a minimum of 4 fibres. There shall be a minimum of 20% spare fibres, but no less than 2 fibres, for future use. All fibres to be terminated in approved terminal boxes. The cables shall be protected from physical abuse and attack from rodents/insects. The Contractor shall advise his proposed methods for the physical protection of the cables and these shall be subject to the approval of the Owner/Engineer. Multipair cables shall be employed for the majority of I&C applications including analogue circuits, up to a maximum of 20 mA, and digital circuits up to a maximum of 50 V dc. This shall include 24 V dc solenoid valves.

5I.2.14.6

Cable installation

5I.2.14.6.1

Separation

Running I & C cables along the same route as power cables shall be avoided. Where this is not possible, the cables shall be segregated as fully as possible. It is not permissible for power and I & C cables to share the same tray/rack/trunking/conduit. I&C cables shall be run on dedicated trays with a minimum separation between the I&C trays and all other trays as specified in 5E. If I&C cable trays are to be installed in the same routes as power cable trays then the I&C trays are to be installed at a lower level than the power cable trays to ensure that heat generated by the power cables does not travel through the I&C cables. A closed conduit I&C cabling system shall be used for individual field devices up to the local junction box.

5I.2.14.6.2

Segregation

All I&C cables from one unit shall be segregated from those for any other unit. The cables for common or station equipment shall be segregated from any unit cabling. Cabling for redundant equipment shall be installed over separate routes. Cabling for redundant instrumentation (eg two-out-of-three voted signals) shall be installed over at least two separate routes.

Specification No. MEW/SOCGT Issued via Addendum No-1, July 2012

5I–104

Contractor’s Initial and Stamp