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The LW42A2-2815/LF406 is a current measurement changeover switch designed for three-phase, three-wire systems using two current transformers, often referred to as an "ammeter phase-changing switch." Its core function is to measure the current in all three phases (phase A, phase B, and phase C) using a single switch and an ammeter, providing a zero-position (OFF) for safety isolation. The product features a black handle and clear function markings, allowing for safe and convenient switching between measurement phases via rotation. It is an economical and efficient solution for measuring three phases with a single meter.
1. Main Technical Parameters
Electrical Parameters:
Rated Insulation Voltage (Ui): 690V
Rated Operating Voltage (Ue): 440V
AC: ≤ 690V, 50Hz-60Hz
Switch Contact Rated Current: 20A (for switching the secondary current signal circuit of the current transformer)
Compatible Current Transformers: Suitable for wiring systems with two current transformers (e.g., connected to phases A and C).
Contact Configuration and Measurement Functions (According to the wiring diagram, "X" indicates ON): Positions and Functions: There are 4 positions, selected by rotating the handle.
Position "0" (OFF): All contacts are open, the ammeter is completely disconnected from the measurement circuit, and the system is in a safe state.
Position "IA": Connect the ammeter to the secondary circuit of the A-phase current transformer to measure the A-phase current.
Position "IB": Connect the ammeter to the B-phase current circuit (calculated from the combined current of the two current transformers).
Position "IC": Connect the ammeter to the secondary circuit of the C-phase current transformer to measure the C-phase current.
Safety Design: Internally, a pre-opening or short-circuit protection design is employed to ensure that the secondary side of the current transformer (CT) will not open during switching, preventing dangerous high voltage.
Mechanical, Lifespan, and Structure:
Mechanical Lifespan: ≥ 300,000 cycles (operation frequency ≤ 120 cycles/hour)
Electrical Lifespan: ≥ 50,000 cycles (frequency ≤ 120 cycles/hour)
Wiring Capability: M3.5 terminal screw specification, suitable for conductor cross-sectional area 1.0-2.5mm².
Key Installation Dimensions (Based on image)
Materials and Certifications: Flame-retardant, high-temperature resistant, and environmentally friendly shell with excellent insulation performance.
Internal thickened copper components and silver alloy contacts ensure low contact resistance, good conductivity, oxidation resistance, and long lifespan.
The product is marked with CCC and CE marks, both conforming to relevant standards.
2. Application Scenarios
This switch is a standard accessory for current monitoring in three-phase three-wire power distribution systems, specifically designed for applications requiring cost-effective and safe monitoring of phase currents.
Core Applications: Three-phase three-wire system current monitoring
Low-voltage distribution cabinet/power box: Installed on the cabinet panel, used in conjunction with two current transformers (usually connected to phases A and C) and an ammeter. Maintenance personnel can easily check the current values of phases A, B (calculated), and C by rotating a switch to determine if the three-phase load is unbalanced, overloaded, or has a missing phase.
Motor Control Center (MCC): Used to monitor the operating current of large motors, pumps, fans, and other three-phase equipment, eliminating the need for independent ammeters for each phase.
Generator sets, UPS output cabinets: Monitor the current of each phase at the output end to ensure power supply balance and safety.
Applicable System Features: Particularly suitable for three-phase three-wire power supply systems without a neutral line (N line) (such as three-phase motor power supply).
The two-CT scheme saves the cost and installation space of a single CT while ensuring basic measurement functions.
