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Assembly design is to be of a modular type allowing the assembly to be broken down into sections for ease of transportation and installation. The preferred module size adopted is 600x600 mm. Height of assemblies must not exceed 2100 mm measured from finished floor level to the highest point of the assembly. Isolator handles, control switches, push buttons, indicator lamps and instrumentation shall not be less than 300 mm and not more than 1,900 mm above finished floor level. Width for terminal compartment will be minimum 400 mm in MCC boards and 800 mm in PLC boards. All cable inlet and outlet for board will be made through IP 65 gland. 

Solid barriers shall be provided to segregate each load compartment from other compartments and the busbar chamber, to prevent objects falling into lower live compartments, and to restrict fault travel to other compartments. 

The finish colour for assemblies shall be the manufacturers standard unless specified in the particular specification. 

Assemblies shall be regular shaped and rectangular, and where possible designed and constructed for floor mounting over cable trenches. 

Minor assemblies may be designed and constructed for wall installation. All cables must enter or exit assemblies through a glanding plate provided with the appropriate sizes and types of cable glands (bushings) from the bottom side of the assembly. 

Reference is to be made to service conditions above for the rating of components and equipment to be installed in assemblies. Further equipment ratings shown on components and equipment must show the values applicable for the ambient conditions. 

## 8.7.3 General electrical requirements 

Assemblies shall be rated for operation on a 400 V AC, 3 phase, 5-wire (TN-S), 50 Hz supply. Control voltages shall be 230 V AC and 24 V DC. The size of the 24 V DC. supply unit is to be based upon actual consumers connected plus future expansions of the plant. 

All components shall function properly within a supply tolerance of -10 % to +10 % on the 400/230 V and -2,5 % to + 2,5 % on the 50 Hz frequency. 

Signals to and from passive instrumentation shall be for analogue 4-20 mA, active or analyser instrumentation communication system should be for Ethernet (TCP/IP) / analogue 4-20 mA , and for digital signals 24 V DC.All component installed in assemblies shall be CE-labelled, and must be capable of withstanding the dynamic and thermal stresses, without detriment, resulting from the prospective fault current. 

The system of tripping devices for the circuit breakers shall be designed and set to ensure full selectivity. E.g. short-circuit in any circuit shall be cut off by the breaker that is closest to the short. 

The branch circuits shall be protected by means of circuit breakers. Fuses may not be used. 

