Bus Duct– Bus-ducts are sometimes used as a replacement of cables. It is used to connect Transformer and LT panel or two panels with each other. Bus-ducts are of two types – 1) Conventional type & 2) Sandwich type.

Bus-duct is made up of metal enclosure in which insulated bus bars are laid & placed with insulated support.Both ends of Bus-ducts are connected with equipment through flexible joints/plats. The purpose of flexible joints is to prevent transfer of vibrations from one end to another if bus-duct is connected with vibrating equipment like transformer.


Rising Mains – Rising mains are used in high rise buildings such as residential and commercial which is installed in electrical shafts. The function of rising mains is to carry electrical supply from LT panel to the top floor of the building & provide tapping point on each floor so that power supply is available on each floor. Rising mains is metal enclosure in which electrical supply is available. Rising mains is installed in a vertical shaft. Tap boxes are mounted on Rising Mains from where electrical supply is taken by the user. Incoming end of rising mains is connected with adopter box & last end (on top floor) is covered with a metal cap. Rising mains is connected with LT panel through cables. One end of cable is connected with LT panel & other end with adopter box.


Function of adopter box – 1) It receives electrical supply (for rising mains) through cable, 2) It provides a switching arrangement & protection for rising mains as it is equipped with ACB/MCCB (depending on the load on rising mains).

Tap Box – It is fixed on the rising mains. It’s a metal enclosure in which switching device like MCCB or MCBs is mounted.  One end of it is connected with rising mains (through flexible wires) & other end is connected with a cable. The other end of cable is connected with load (like main panel of office or meter panel of the flatetc).

PLC– PLC stands for Programmable Logic Control – It is used to control sequential switching on or off Incomers of Transformers (means govt supply), DG sets & Bus Couplers. Its an electronic relay which helps for –

  • To start DG sets automatically when transformer power goes off,
  • It checks the load requirement & selects the number of DG sets which are to be started.
  • A logic diagram is prepared according to the load requirement & fed in the PLC and accordingly incomers (DG feeders) & bus-couplers are switched on/off.
  • In logic diagram one DG is kept as a mater DG & other DG sets are kept in sequence (or in queue). When transformer supply goes off, first master DG switched ON & feeds the load, if load is more than the capacity of master DG, then other DG sets which are in queue (kept in sequence for operation) are switched on.
  • Master DG set can be changed as per requirement.
  • It can switch on & switch off DG auxiliaries like pumps & cooling towers automatically,
  • It can operate bus-coupler also according to the load requirement,
  • When transformer supply is restored, all DG sets switched off automatically including its auxiliary pumps etc.