SWITCHBOARD METERS

These instruments consist of a moving piece of ferro magnetic material, which is under influence of a current carrying fixed coil. Considering the quadratic nature of the deflecting torque, the scale of these instruments is non-linear. Considering the above mentioned operating process, these instruments are ideally suited for measuring TRMS current and voltage in alternating current circuits. Ammeters are mostly used alongwith externally mounted current transformers, though ammeter upto 100A for direct connection are also provided. Voltmeters upto 750V can be provided. Ammeters with over scale suppressed scale of 2xIn and 6xIn to withstand high and very high motor starting currents can also be provided. Accuracy for these meters is applicable only within the nominal working range and not in the overscale range.
However please note that all Ammeters can withstand an overload of 10 times the rated range for maximum 5 sec. and 2 times rated currents continuously. When using external current transformer, please ensure that the secondary current value of the CT must be the rated current of the Ammeter i.e., In.