(i) In case of inductive loads of POFs below 0.5, the torque of one element reverses, but the net torque as both elements is still proportional to the power and is in the forward direction, but of two single phase energy meters are used for measurement of energy in such load circuits one will register in the reverse direction and, if this results in a net reverse registration of that meter over a period of time, there is a possibility of confusion.
(ii) The reverse registrations are liable to be in serious error because the friction compensation of the meter is for the forward direction of rotation.
For three phase, four wire circuit it is more satisfactory to employ three single phase meters, the connections are similar to those of 3-watt meters in 3-phase, 4-wire circuits for measurement of power. When the currents and voltages of the circuits to be measured are high then use of instrument transformer (CTs and PTs) is made with energy meters just as with wattmeters. If the line voltage exceeds 400V, current transformers and potential transformers are almost invariable used respective of magnitude of current in order to insulate meter from the line.
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