ELECTRICAL AND COMMUNICATION INSTALLATION DESIGN IN AN OFFICE COMPLEX PROJECT INDEX: PRJ017 BY F17/1765/2006 MUTUMA WALTER MURIMI SUPERVISOR: PROF. E. MWANGI EXAMINER: DR. J. MBUTHIA DATE: 27 th MAY 2011
OBJECTIVES Lighting Design Power Points Design Fire alarm system Load Balancing Power Distribution Layout Cable Sizing Communication system design
Lighting Design Lumen method was adopted for this design. Daylight factor was estimated and included in lumen equation as per building services code. Lumen method equation Room index equation N = E x A Ф x M.F x U.F x D.F K = L x W H (L + W)
Sample Lighting Calculation For example, total illuminance required for biological science lab was 300 lux. Room Index K = 12 x 8 = 1.6 3(12+8) Utilization factor (U.F) = 0.47, daylight factor obtained = 1.75, maintenance factor taken as 0.9. Thorn T26 battens of 1200mm length, twin 36W fittings with 6700 lumens were used. Number of fittings: N = 300 x 12 x 8 = 5.81, approximately 6 6700 x 0.47 x 0.9 x 1.75
Lighting layout for the biological science lab
Fire alarm and security system design Fire alarm system installation fulfils the following functions: Indicate clearly the escape routes, Provide illumination on such routes for safe evacuation from the building, Ensure fire alarm call points and fire equipment provided along the escape routes can be easily located and used, Permit operations concerned with safety measures.
Fire alarm and security system in the building
Power points design Power points laid out in accordance to IEE recommendations on wiring of 13A final sockets. 30A MCB could support a load of 7200W. Taking a load of 500W per single socket, a ring could have 7 twins or 14 single outlets. Provision was given for TPN isolators in the machine workshop as well as double pole switches for handriers and fans in other areas.
Power points Layout for machines workshop
Sample calculation for ground floor load Lighting load = Tot. light fittings Worst case load diversity = 188 100 0.9 = 16920W Power point load = 100% of 1 st ring circuit + 75% of remaining ring circuits = 7200 + (7200 7 0.75) = 45000W Single phase isolator load = (12000 + 80% 7200 + 60% 21600) = 30720W. Three phase isolators load = (19408 + 50% 135853) = 87334W Thus, total Ground floor load ( with diversity factor) = 179,974W
Load Balancing Done for every DB, floor and then the whole building. The lesser load on a DB was compensated on the next DB. Three phase loads were equally distributed through the 3 phases on ground floor. Phase with larger load on one floor deliberately given a lesser load on the next floor.
Summary of Ground floor Load Balancing Table 3.9 Load balancing on DB 3 Description Red phase Yellow phase Blue phase 30A 30A 30A 6A 6A 6A 6A Totals 42A 36A 36A Table 3.15 Load balancing on ground floor Description Red phase Yellow phase Blue phase DB 1 88A 88A 86A DB 2 18A 30A 30A DB 3 42A 36A 36A Totals 148A 154A 152A
DB Protection The consumer loads were allocated DBs after allowing for diversity. For instance for DB6, load after applying diversity was obtained as (50A + 75% of 50A + 90% 0f 18A) = 103.7A, therefore a 150A MCCB would be appropriate. Consumer ways were protected by MCBs of rating slightly higher than load on that way. The DB isolators had a rating of between 100A and 200A (MCCBs).
Sample way allocation on DB2
Distribution Layout Diagram
Cable Sizing Done to satisfy IEE regulations. Voltage drop from source to fixed equipment not to exceed 4% of the declared nominal voltage. Cables selected with reference to IEE tables. Voltage drop was calculated as per the formula: For example, for DB7, voltage drop (V) = (100A x 1.1mV/A/m 50/1000) =5.5V which was less than 4 per cent of 415V.
Protection system design Protection systems included: Earthing PME system. Lightning protection done using an air termination (lightning rod) together with several horizontal and vertical conductors positioned strategically on the building.
Communication system design This involved telephone circuitry, television connections and data cabling for computers. The data cabling was done through a 200mm 50mm metallic trunking. A private automatic branch exchange (PABX) with 20 extensions was also incorporated in the design for telephone switching.
Communication system layout showing the PABX
Conclusion and future recommendations The objectives of the project were met as complete installation design of electrical and communication systems were done. Fault currents are to be determined for the various protection devices used as well as the protection system.
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