Engineering Project Cable Management

Rising Main Installation General Forms the skeleton of the electrical distribution system as shown in figure 1.1 and should comply with the following: Any building of more than four floors including the ground floor should be provided with 3-phase electrical rising mains with a 3-phase 4-wire tee-off at each floor.

Separate riser earthing conductors should be provided to earth all units. The minimum cross-sectional area of riser earthing conductor should be 70mm² for copper and 150mm² for aluminum. No aluminum or copperclad aluminum conductors shall be used for final connections to earth electrodes. The consumer’s main connection between the Electricity Company’s meter and the consumer’s main switch should be installed and maintained by the consumer and should be not less than 4mm² stranded copper conductors.

In multi-consumer premises a device capable of both isolating and switching the full load current of the whole installation should be provided for each consumer at a position immediately before the Electricity Company’s. For a single phase installation this device should be of double-pole type interrupting all live conductors.

The maximum copper loss in every main riser should not exceed 2 The maximum copper loss in every main riser should not exceed 2.5% of the total active power transmitted. In multi-consumer premises no part of the communal installation should pass through any individual consumer’s unit within the building.

The Electrical Schematic Wiring Diagram

Selection of Type of Rising Main The following factors affect the selection of the type of rising main: - - Load assessment - Load distribution - Environmental conditions such as ambient temperature, grouping and humidity - The heights of riser - Voltage drops - Fault level - Future expansion

Types of Rising Main Cable Busduct

CABLES Following cables are widely used in the electrical riser main, Single core cables with double insulation, - Four core armoured cables, - Prefabricated branch cables and , - Four cores armoured cables with fire resistant for fire services equipment.

Multi-core armoured cable Prefabricated branch cables

The selection of cable as rising mains is limited by its current carrying capacity (CCC). For a single-core, p.v.c.-insulated, non-armoured cable, the largest c.s.a. is 1000mm² giving a CCC of 1149A. As a rule of thumb, when the demand exceeds 800A, busduct is preferred.

Insulated Busduct Rating of busduct: up to 3000A or even higher Feeder type and plug-in type The provision of plug-in unit provides flexibility for tee-off at any location/floor at any time when demand required. Figure 1.3a & 1.3b shows the arrangement of busduct system for building and factory

Figure 1.3a For High Riser Building Notes: 1) End closure / end cap 2) Switch board 3) Plug-in box 4) Flatwise elbow 5) Edgewise elbow 6) Flanged end 7) Transformer 8) Cable tap box 9) End cable tap box

Figure 1.3b For Factory Building Notes: 1) End box 2) Plug-in box 3) End cable tap box 4) Plug-in box 5) End closure /end cap

Sub-Main Cables Installation General The sub-main cables installation from the riser main branch off to the power distribution centre at each floor as shown in Figure 2.1 The maximum copper loss in every sub-main circuit shall not exceed 1.5% of the total active power transmittal. The sub-main distribution for the building, the lighting and power sub-circuit will be supplied by separate distribution boards as shown in Figure 2.1.

Figure 2.1 Sub-Main Cable Installation

Selection The following factors affect the selection of the type of sub-main cables: - - Load distribution area; - Environmental conditions such as ambient temperature, grouping and humidity if the load centre is far away the main riser; - Voltage drop consideration if the load centre is far away the main riser and; - Future expansion.

Types of Sub-main Cables In general, the following cables are widely used in the sub-main cables, - Single core cables with mechanical protection e.g. conduit or trunking; - Single core cable with double insulation e.g. PVC/PVC cable and; - Single core cables with fire resistance for fire services equipment, e.g. cable comply with BS 6387

Final Circuits Final circuit using 5A or 15A socket outlets Circuit Radial final circuits should be used. Protection Each 5A and 15A socket outlets should be connected and protected by a high breaking capacity (HRC) fuse or miniature circuit breaker (MCB) of rating 5A and 15A respectively.

Standard 5 A or 15A socket outlets comply with BS546. “ Two pole and earth pin plugs, socket outlet and socket outlet adaptors are used for single phase final circuit.”

Final Circuits Using 13A Socket Outlets Ring or radial final circuits should be used. The circuit, with spurs if any, may feed permanently connected equipment and an unlimited number of socket outlets in a limited floor area determined by Table 3.2 A typical circuit is illustrated in Figure 3.2a.

Spurs For a final circuit in compliance with Table 3.2 the number of fused spurs connected is unlimited but the number of non-fused spurs should not exceed the total number of socket outlets and fixed equipment permanently connected in the circuit. A non-fused spur should feed only one single or one twin socket outlet or one permanently connected equipment. Such a spur should be connected to a circuit at the terminals of socket outlets or at joint boxes or at the origin of the circuit in the distribution board.

(iii). A fused spur should be connected to the (iii) A fused spur should be connected to the circuit through a fused connection unit, with the rating of the fuse not exceeding that of the cable forming the spur, and not exceeding 13A in any event.

Table 3.2: Final Circuits Using 13A Socket Outlets Type of Circuit Rating of Overcurrent Protective Device (HRC fuse or Miniature Circuit Breaker) (Ampere) Rating of Overcurrent Protective Device (HRC fuse or Miniature Circuit Breaker) (mm²) Maximum Floor Area Served (m²) A1 Ring A2 Radial A3 Radial 30 or 32 20 2.5 4 100 50

Fig. 3.2a Typical Final Circuit Using 13A Socket Outlets

Separate circuits Separate circuits are to be used for: Socket outlets and fixed appliances in kitchens (preferably); (ii) Electric water heaters; (iii) Permanently connected space heaters and (iv) Air-conditioning units.

Final Circuit Using Raised floor Trunking System Raised floor trunking system provides a solution for distributing power, telecommunication and data services to user level by way of floor outlet boxes.

Useful for open plan and partitioned office and can be installed within raised platform floor. Locations of floor services boxes can be easily changed to suit the furniture Accessory modules of services box can be selected from wide range of services power and data options to suit all applications

Metering