Electrical Installation Design

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Residential Installation Design

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Chapter 1: Design Concepts
1.1 Design Requirement
• • • • • • • • • • General provision of 13 A switched socket outlets (SSO). Each circuit to serve not more than 50 m2 of floor area. Additional SSO to be provided at specific location for known appliance e.g. kitchen, living and family areas, Not more than 3 nos. of SSO connected to a 20A circuit serving kitchen area, One number of multi-split air-conditioner unit ( assume 3 kW, pf=0.85) provided with isolator point (20A) located at the Yard area, Water heater (instantaneous type) 2 kW located in bathroom, Each lighting circuit should not be connected to more than 10 lighting points, Fluorescent lamps are to be provided in the kitchen and store room, One consumer unit located at the entrance/store room, One meter kiosk located at the entrance, . Use appropriate diversity factors in your calculations and explain why the values are used.

1.2 Design rules for lighting circuit • To indicate the location clearly


To indicate the switching arrangement

One way switch control

Two-way switch control


L1: same circuit number indicate that they are from the same MCB control by the same switch

: One way switch

: two gang switch

: two way switch

General rules
1. 2. 3. 4. 5. 6. Assume a maximum rating of each lighting point is 100W Not more than 10 lighting/fan points in a circuit No switch should be located inside bathroom Use 6A or 10A SPN MCB Use 1.5 sq mm cable size For discharge lamp without exact information, the loading of circuit be determined by multiplying the rated lamp power (watts) by a factor 1.8 I=p*1.8/V This multiper takes into consideration a circuit power factor of not less than 0.85 lagging, and also control gear losses and harmonic currents.

1.3 Design rules for switched socket outlet
• • • • • Not more than 3 SSO ( 15/20 A MCB, 2.5 sq mm) serving area including kitchen Not more than 6 SSO ( 20A MCB, 2.5 sq mm cable) serving a room which is not a kitchen Not more than 6 SSO (30A MCB, 4 sq mm cable) serving area including kitchen Not more than 10 SSO (30A MCB, 2.5 sq mm cable) in ring circuit. No socket outlet is allowed inside the bathroom



1.4 The difference between radial and ring circuit for switched socket outlet Ring circuit

Radial circuit

The summary of main difference

1.5 Design requirement for heater
1. Each heater must be connected to its own final circuit 2. The minimum breaker size is 15/20 A 3. Minimum cable size is 2.5 sq mm


1.6 Design rules for air-conditioner
1. Supply from 15 A switch socket outlet for window unit. 2. Supply from isolator for split unit type of air-conditioner Split unit—compressor (outdoor) Fan (indoor) Room A/C unit—must have one side facing outside 3. A/C unit is basically motor load, therefore with high starting current and starter may be used. 4. For multi-split A/C unit, one compressor can serve a few areas. Only one isolator is required. 5. For room A/C unit, each unit must be served by a 15 A switch...
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