Indicating lamps, terminal blocks, and test terminal blocks. This topic covers use of indicating lamps, use of terminal blocks, types of terminal blocks, RTB, need for test terminal blocks or TTB. Indication lamps are utilized to indicate the status of equipment, say open, or closed, or even abnormal conditions. These lamps get eliminated when the assigned status condition is met. Indicating lamps are used to indicate the equipment status, such as on, off. For on-switching equipment, CB, or isolator, or earth switch, trip circuit healthy, spring charged, heater on, motor running, motor stopped, valve open, or close, etc. The illuminated type push button is also available combining the functions of both the push button and indicating lamp so that the panel surface area may not look cluttered. Standard colors used are similar to the PB actuators. IEC 60073 is followed for lamp colors, red for equipment on or motor running status. Green for equipment off or motor stopped status, amber for indicating fault or abnormal conditions. White or blue for other normal or healthy conditions. In switch gear, blue is used for CB spring charged condition, white for trip circuit, healthy condition. Traditionally, filament lamps with colored lens have been provided for indicating lamps. As filament lamps are susceptible to frequent failure, LED lamps are preferred nowadays. While individual lamps are provided for dual status, like open or close, on or off, only single lamp is generally used for feeder auto tripped, or spring charged, or heater on, or trip circuit healthy conditions. If the lamp heater on is fused out, can the status be not misunderstood? What can be done to prevent or avoid misreading of such signals. For this purpose, a test push button, common for all indicating lamps is provided. When this PB is actuated, voltage is applied across all lamps, bypassing the assigned status conditions momentarily. This way, fused lamps are identified and action will be initiated for a replacement. As LED lamps are expected to have a long life, test PB is not preferred by some manufacturers. Terminal blocks or TBs are modular, insulated blocks that secure two or more wires together. External cabling is connected to instruments placed inside the panels through terminal blocks. Terminal blocks are tagged and numbered for easy identification. Note the wires dominated have imprints on the ferrule. Imprints into the TB tag or number and code for identifying device connected on the other side. This would help one to reconnect at the right place without any confusion and for testing purposes. Several types of TBs are available based on function and type of connection. Some of the common types are based on function. Fuse type, warehouse control fuse module, disconnecting type, shorting type, built-in facility too short to adjacent TBs used for CDs. Based on the type of connection, screw type for terminating pin-type plug, star type for connecting ring-type plug. Test terminal blocks are used to test meters and protective relays to enable testing of instruments without any need to disturb the panel wiring when the panel is in life condition. Invariably, all protective relays are provided with a dedicated TTB recommended by the manufacturer of the same relay. You know accidental open circuiting of CT and short-circuiting of VT would damage CDs and VTs respectively. TTB help us in carefully handling CT or VT wires in a structured way. TTB also helps in carrying out secondary injection tests on the protective release or meters when the circuit is life without availing shutdown of the equipment. Here is a quick recap of what you have learned this far. Indicating lamps are used to indicate the equipment status, such as on, off for all switching equipment, CB, or isolator, or switch. Trip circuit healthy, spring charged, heater on, motor running, motors stopped, valve open or close, etc. Standard colors of indicating lamps are used in switch gear panel as per IEC 60073. LED lamps are used instead of a filament lamps due to better service life. Terminal blocks or TBs secure two or more wires together. Terminal blocks are classified based on function and type of connection. Shorting type, isolating, stand, fuse type, or types of terminal blocks. Terminal blocks and terminated wires are tagged and numbered for easy identification. Terminal blocks or TTB facilitate meter and protective relay testing in live panels through secondary injection.
