As the quest for change over on public power supply and stand by generation increase. Engineering have researches deep into the different methods of achieving to both manual and automatic types.
It may not be taken seriously in some places where power supply is up to 90 constant or where intermittent outage causes no great damage. However, place where they have business centers, industrial centers and even cold rooms need to almost 100% supply. So in this case there is need to provide a standby power supply in the event of power outage. The most important task is just to provide a standby power supply by great attention is paid to the reliability of the system. That is immediately and change over without fluctuations.
The first type of change over switch were purely manual operated. They usually have three switch able position, main, off and generator. An arm is provided from where the operator can have access to the switching. Here, the effectiveness of the switching (i.e how fast it is effected each time power needs to be changed) largely depends on the operator. The change over system will be ineffective when the operator is not around.
The second generation of change over switches were made semi-automatic in which the mains power supply directly powers the contactors. This arrangement is wired is such a way that if the mains power supply fails, the contractors will all drop leaving the supply to the generator position. The effectiveness of the system will now depend on the operator top start up the generator on time.
The main problem suffered by the above mentioned two versions of the change over switch is that the operator must have to be continuously on duty for it to be very effective. They lent use full closed loop system to operate.

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