Incandescent lamp for monitoring phase loss in three-phase electric water heater

The circuit of the three-phase electric water heater is monitored by an incandescent lamp, as shown in the figure. RL1~RL3 in the figure are three electric heating tubes, and the figure adopts the star connection method, namely "Y connection method". A common 220V/4W bulb is connected between the center point 0 and the ground wire N. According to the change of the brightness of the incandescent lamp, the fault of the running three-phase water heater can be determined; when the three-phase water heater is running normally, the center point O and N are at the same potential, and the incandescent lamp EL is not bright; when one phase of the water heater electric heating tube is burned out, the center potential of the water heater is about 110V with N, and the current flowing through the bulb is about 1/2 of the rated current of the bulb, and the filament is red: when two phases of the water heater electric heating tube RL1~RL3 are burned out, it is equivalent to one phase of the water heater running connected in series with the incandescent lamp and connected to the 220V power supply of the mains. Because the resistance value of the bulb exceeds the resistance value of the water heater electric heating tube, the voltage applied to both ends of the incandescent lamp is close to 220V, so the bulb EL appears very bright.

In tea making, RL1~RL2 are the electric heating tubes, usually 1.5kW. EL can be installed on the power distribution board. If it is not lit at ordinary times, it can be considered that there is a fault.