DESIGN CONSIDERATIONS FOR ELECTRICAL SERVICES

Design Considerations for Residential Houses, Multistory, Multiflat Buildings; Office blocks, factories and Public buildings.

Some of the design considerations are outlined below. It should be noted that the experience of the engineer is very important in design.

Architectural and Structural Drawings.

In most projects, the Electrical Engineer forms part of a design team. This team include other service engineers and the Architect. Other members of the team provide information which the engineer utilizes for his design. The Architect and the Structural Engineer provide the Electrical Engineer with both architectural and Structural drawings which are used by the Electrical Engineer for Electrical Services Design Work. Some of the information provided by these drawings include: the nature, location and intended use of the building of interest; the location of beams and columns, and cantilevers; as well as other details which would be of interest to the engineer and which will influence the design subsequently.

Luminous Level and Electrical Facilities to be installed or provided for.

A good understanding of the proposed project would enable the Engineer determine the appropriate Electrical Facilities to be installed or provided for within the limits of available resources. This calls for good client consultant relationship for proper understanding of the needs of the client as well as the recommendations of the consultant. The Luminous requirement of the various parts of the building is also determined.

Selection of Fittings, Luminaires, Cables and other Facilities

 Calculations are carried out to determine the appropriate fittings and cables as well as other facilities required to meet the design specifications laid down by the Engineer. These calculations are consistent with the principles we have studied in this course (Electrical Services Design) up till now. The calculations are however modified to make room for peculiarities of circumstances.

The design is carried out in such a way as to meet basic standards and regulations guiding such work and design. When the appropriate number of fittings has been determined, the next step in the design can then be taken.

Load Analysis

The Load analysis is then carried out making provision for diversity factors where appropriate. This has to be in line with regulating standards. The result of the load analysis will determine the service cable sizes as well as the kind of installation required in addition to protection and control.

Protection and Control

The result of the Load Analysis is now used to determine the kind of Protection and Control required for the proposed building. The number and type of Distribution Boards and their current and Voltage specifications can be determined using the results of the Load analysis. In addition to this, the switch gears are also determined in a similar way. The control and protection of each final sub-circuit is determined likewise. When this exercise is concluded, the Engineer would then specify the ratings, type and number of all protective and control devices along with the associated cables for proper connection.

Appropriate drawings are produced at each stage of the design.

Bill of Quantities

Electrical quantities are extracted from these drawings. ( These bills are used for tendering by contractors.) The current prices of items and quantities are used to estimate the cost of the proposed project. Provisions are made for fees, Labour and variations as a result of inflation and price fluctuations. This is very important as cost is a very important factor in Electrical Services Design.  

Tests

Tests are recommended by the Engineer. These tests are carried out at the end of the project before the completed work is handed over to ensure that the design specifications are met.

During construction, provision has to be made for proper supervision.

NB.

Provisions are made in the design for telephones, fire alarm systems, computer systems, Telephone, internet and other audio/visual aids and facilities depending on the intended use of the building.