External Roesch coil and split-core transformer harmonic meters with guide rail design, suitable for energy-saving transformation projects in high-energy-consuming industries such as smelting, steelmaking, welding, and semiconductor manufacturing. Also applicable to power monitoring and demand-side management for distributed photovoltaic grid-connected cabinets. Features include no need to dismantle the main busbar, simple and convenient wiring, safe construction, cost savings for users, and improved efficiency. It integrates the measurement of all power parameters (such as single-phase or three-phase current, voltage, active power, reactive power, apparent power, frequency, power factor, etc.), dual-rate energy metering, four-quadrant energy metering, harmonic analysis, and energy monitoring and assessment management.