Recently we faced and issue with furnace oil powered boiler , which was preheating overheated. we checked the heates which were 3 phase . current consumption was balanced in each phase and resistance was same in each one. cable was insulated properly .
We noticed some loose connection on cable lug point we tightened that and covered the heaters. then we stated but issue was same . temperature was suppose to cut off by 110’c but the current temperature going up to 200+’ c. so we assumed its the issue with supply which doesn’t cut off. soe we noticed the siemens auxiliary contactor is stuck and doesn’t operate. Command was given by tc544 Selec PID controller. It was a NO connection. but we didn’t have simen spare parts so replace the contactor by Schneider contactor which worked perfectly fine.
Above the contactor supply came form MCB 40A. Heater on off command was given from another contactor . FO (Furnace Oil) temperature was sent from the RTD which was connected to pre heater .
