CHAPTER ONE
1.1     INTRODUCTION
Change over switch is a device used to switch off a power supply and subsequently switch on another power source. Basically it is aimed at switching on a more convenient power supply to the load. Since it switches on power to the load precaution has to be taken while choosing the type of change over switch. Also size, arcing control are put into consideration in the choice.
          A good switch should be the one whose contact is made in such a way as to limit the arc formation by having no contact-bounce and by having contacts made of good conductive, corrosion resistance and wear resistance materials.
          A good change over switch must have adequate insulation and must be so constructed and located as not to constitute a potential hazard.
          A good change over switch should also have tight contacts so as to limit or eliminate the possibility of partial contacts at the contact point. The partial contact lead to over heating of the components and may lead to fire out break.
1.2     Aims and Objectives
Due to inconsistent supply of power, there is a growing need for an alternative source of power supply. This has led to heavy capital investment in a bid to curb power failure and ensure regular power supply for our industries, hospitals and homes. The problem of power failure can be checkmated with the use of standby generating set.
An Engineering author Tony Rudk Inn said in his book titled "Upgraded signal source with improved performance and reliability" that the cost and depreciation associated with breakdown vary from one application to the other, and in some cases, the user has little choice but to ensure that a stand-by unit is available to take over on event of failure of primary system.
          If some of these big firms do not make provisions for stand-by power source, frustration could set in which may lead to the closure of business and thus throwing workers into unemployment. Also in the case of hospitals undergoing a surgical operation and the power supply suddenly goes off, the patient might loose his life due to power outage.