15.6 Control Cabinets / Panels / Desks
i) The cabinets shall be IP-22 protection class. The Contractor shall ensure that the packaging density of equipment in these cabinets is not excessive and abnormal temperature rise, above the cabinet temperature during normal operation or air-conditioning failure, is prevented by careful design. This shall be demonstrated to the Purchaser during the factory testing of the system. The Contractor shall ensure that the temperature rise is limited to 10 deg. C above ambient and is well within the safe limits for system components even under the worst condition Ventilation blowers shall be furnished as required by the equipment design and shall be sound proof to the maximum feasible extent. If blowers are required for satisfactory system operation, dual blowers with blower failure alarm shall be provided in each cabinet with proper enclosure and details shall be furnished with proposal. Suitable louvers with wire mesh shall be provided on the cabinet.
ii) The cabinets shall be designed for front access to system modules and rear access to wiring and shall be designed for bottom entry of the cables.
iii) The cabinets shall be totally enclosed, free standing type and shall be constructed with minimum 2 mm thick steel plate frame and 1.6 mm thick CRCA steel sheet or as per supplier’s standard practice for similar applications, preferred height of the cabinet is 2200 mm. The cabinets shall be equipped with full height front and rear doors. The floor mounting arrangement for other cabinets shall be as required by the owner and shall be furnished by the Contractor during detailed engineering.
iv) Cabinet doors shall be hinged and shall have turned back edges and additional braking where required ensuring rigidity. Hinges shall be of concealed type. Door latches shall be of three-point type to assure tight closing. Detachable lifting eyes or angles shall be furnished at the top of each separately shipped section and all necessary provisions shall be made to facilitate handling without damage. Front and rear doors shall be provided with locking arrangements with a master key for all cabinets. If width of a cabinet is more than 800 mm, double doors shall be provided.
v) Two spray coats of inhibitive epoxy primer-surface shall be applied to all exterior and interior surfaces. A minimum of 2 spray coats of final finish colour shall be applied to all surfaces. The final finished thickness of paint film on steel shall not be less than 65-75 micron for sheet thickness of 2 mm and 50 microns for sheet thickness of 1.6 mm. The finish colors for exterior and interior surfaces shall conform to following shades:
a) Exterior:- As per RAL 7032 or as finalised and specified during detailed engineering.
b) Interior:- Same as above.
Paint films which show sags, checks or other imperfections shall not be acceptable.
vi) Cabinets shall be designed for a grounded installation on the building structure. Any isolation from the building ground which is required by equipment design shall be provided internal to the cabinet.
vii) The mimic shall be configured on the OWS/CRTs and it shall be possible to control, monitor and operate the plant from the same.
viii) Ammeters will be provided on control panel for All motors rated 30KW and above. Further, HT/LT switchgear voltmeters shall be provided on control desk for HT/LT feeders. Ammeters and voltmeters shall be suitable for 4-20 mA DC signals derived from Analog Output cards of PLC.
ix) Mosaic based control desk type for mounting push buttons/meters etc. with door at the rear shall be provided by the contractor. The mosaic grid tiles shall be of 24mmx48mm (or 25 mmx50 mm) size, made of heat and flame retardant, self extinguishing and non hygroscopic material with flat-matt finish without glare and non reflecting type. PC based OWS(operator Work Station) of PLC shall be mounted on table type control desk to house PC/ keyboards/ mouse etc. The profile and dimension shall be decided during detailed engineering and shall be subject to Owner’s approval.
15.6.1 Panels and wiring
i) Interconnecting wiring shall be provided between all electrical devices mounted in the panels, desks, consoles etc. The equipment outside the panel shall be connected through terminal blocks only, except for other special circuits.
ii) Wiring to each control switch shall be individually bunched and shall be installed with a “drop loop” of sufficient length (not less than 750 mm) to allow the item to be removed from the panel for maintenance without disconnecting the wiring.
iii) Wire sizes for various applications shall be finalized during detailed engineering. However, the wire sizes shall be limited to 0.5,1,and 2,5 sq. mm cross section, stranded copper.
iv) Color code/size etc. for control & instrumentation cable shall be finalised during detailed engineering..
v) Common connections must be limited to two wires per terminal.
vi) All panels/desks/consoles internal wiring shall be tinned copper, stranded conductor, flame retardant cross linked polythylene (XLPE) insulated as per relevant standards.
vii) Panel, desk console wires shall be identified with wire number at each termination by means of split sleeve or indelible tubing markers. The ferruling system shall be finalised during detailed engineering.
viii) Terminal lugs furnished must be of the compression, insulated sleeve, ring tongue type. Open-ended terminal lugs will not be accepted. Wires shall not be looped around the terminal screws or studs.
ix) Wires shall not be tapped or spliced between terminal points.
x) Instrumentation wire shield connection shall be individually terminated on terminal blocks. Shield termination shall be made on terminal blocks adjacent to the enclosed wire terminations.
xi) Contractor shall group the internal wiring so that all out-going wiring to each particular remote location is terminated on adjacent terminal blocks.
xii) Panels, desks, consoles will be provided with removable gasketted cable gland plates and cable glands for all floor slots used for cable entrance. All openings at the bottom shall be sealed to stop the entry of vermins in the panels. There shall be sufficient space provided for easy fixing and removing of all external cables. Sufficient space must be provided between the terminal blocks and cable leads for easy replacement
