BS 37-5:1955

Maximum demand meters, combining energy elements (motor type) registering in kWh or MWh, maximum demand indicators (mechanically coupled) or suitable for fitting such indicators, indicating in kW or MW, and timing elements; not the timing elements which may or may not be contained in meter case, not meters depending on balanced conditions of load or supply, not precision meters. Types (a) Whole-current and transformer-operated, for 2-phase, 3- or 4-wire supplies, (b) Whole-current and transformer-oper ated, for 3-phase, 3- or 4-wire supplies.