Planning and Designing of Electrical Installations

Planning and Designing of Electrical Installations Points : planning and designing of electrical installations , steps of consideration at design stage, every design must consider, flexibility, accessibility, reliability Until recently a building used to be designed and built before even the electrical services were considered. They were an after-through and no one contemplated asking an electrical engineer for his opinion at the design stage. Nowadays with the tremendous growth in the number of electrical appliances and the vast increase in demand for electricity, the architect has to design a building with the electrical services very much in mind. Steps of Consideration at Design Stage This first and foremost question when planning an installation is whether there is, a supply of electricity available. If there is, how near is it to the proposed building site, is it just across the road or a mile away? If it is a long distance away, what are the charges to bring it to the site and how long will it take the Supply Company to make the connection? Although most supplies are now standardized at 440 volts 3 phase a.c., and 250 volts single phase ac., it is wise to check this.

Before approaching the Electricity Supply Company, the engineer should know the approximate lading of the installation, probable future requirements, and the limes when the maximum loading will occur. It can then be confirmed whether the required power can be supplied all the time, or whether there will not be sufficient at peak periods etc. If the latter is the case, either the layout will have to be redesigned and less power consuming apparatus installed, or else an auxiliary generating plant may be installed, but this could be very expensive.

Depending on the customer’s requirements and the type and size of installation, different tariffs can be charged for electricity consumed. In small or medium size installations, such as houses, shops, office etc, separate tariffs are generally charged with separate meters for light and power. With large industrial installations a single tariff is charged, base on the fact that the lighting is guaranteed to be under a specified percentage of the total load. In this case, only one set of meters is installed by the Supply Company.

If an installation contains a large number of single phase loads such as heating or drying apparatus, banks of lights etc. and a three phase supply is brought in, then the electrical engineer must make sure that the load is divided equally among the three phases. If heavy loads are not divided equally, the supply over a wide area becomes unbalanced, leading to. large variations in single phase supply voltages and heavy neutral currents in the supply cables.

A point which the design of a building must allow for is changes of tenancy. If the building is, an office block rented out to various firms, then just because the first tenants do not want air-conditioning. If this possibility has not been catered for, then the owner is faced with a large programme of rewiring with all the expense and inconvenience that it entails. Every Design Must Consider Flexibility Depending upon the type of building industrial, commercial or institutional the electrical system must be designed to provide required flexibility in distribution and circuiting. Feeders, distribution panel boards and circuits should be suited to a wide range of utilization patterns. allowing full and efficient use of power capacity for activities in the building’s various areas. Accessibility Every electrical system should rate high in accessibility. In its final form, design of the system must provide ease of access to equipment for maintenance and repair and for any possible extensions, modifications or alterations in the system. Reliability Depending upon the nature of activities is a building, continuity of electrical supply and over-all reliability of the wiring system itself can be a mere or less important consideration. But in many industrial plants, hospitals and buildings with essential equipment electrically powered, standby power plants or multiple services must be used for absolute reliability of supply.