This product features optical signaling of voltage levels in three phases. Each phase has LED signaling divided by colour to indicate different voltage levels. The green LED indicates voltage within the tolerance range of ±15 (207 to 264.5 V/253 to 195.5 V). The red LED indicates overvoltage (264.5 to 276 V/276 to 253 V). The yellow LED indicates undervoltage (50 to 207 V/195.5 to 45 V). If the voltage is below 50V, the LED will not illuminate. This product operates on a 3 x 400/230 VAC supply voltage and has a width of 17.5 mm per module.