Overview
The Amprobe A-400 (often cataloged as the A400) is an alternating current (AC) clamp-on transducer engineered to extend the measurement capabilities of standard test instrumentation. By transforming magnetic fields surrounding an electrical conductor into a proportional low-voltage signal, this accessory permits high-amperage current evaluations without necessitating inline circuit disconnection or hardwired series installations.
Technical Specifications
| Attribute | Details |
| Manufacturer | Amprobe |
| Product Category | AC Current Transducer |
| Current Measurement Range | 0.1 Amperes to 400 Amperes AC RMS |
| Output Signal Transformation | 1 millivolt AC per 1 Ampere AC |
| Operational Frequency Band | 50 Hertz to 60 Hertz |
| Maximum Working Voltage | 600 Volts Category II (IEC 1010-1) |
| Output Impedance | 75 Ohms maximum |
| Maximum Jaw Opening | 30 millimeters (1.18 inches) |
| Maximum Conductor Capacity | 29 millimeters (1.14 inches) diameter |
| Dimensions | 148 millimeters long by 72 millimeters wide by 36 millimeters deep |
| Unit Weight | 250 grams |
Physical Description
The instrument utilizes a specialized pistol-grip architecture molded from impact-resistant, high-dielectric composite polymer. The top section features two spring-loaded transformer jaws configured to encircle isolated branch conductors, operated via an integrated mechanical thumb trigger located on the side of the housing body. A structural hand guard ridge is integrated directly below the jaw mechanism to minimize user exposure to uninsulated, current-carrying infrastructure. Connection interfaces consist of an attached coiled output cable terminated with standard shrouded banana test leads.
History
The A-400 transducer assembly was developed by Amprobe to solve test infrastructure limitations associated with early solid-state multimeters, digital oscilloscopes, and automated power logging recorders. During the transitional testing era, many standard portable benches and hand-held multi-meters lacked direct internal shunts capable of processing higher current loads without overheating internal micro-circuitry.
By designing an external transformer accessory built on a millivolt conversion standard, operators could evaluate electrical distribution lines up to 400 Amperes using standard low-voltage multi-meter functions. The design was produced to serve commercial electrical technicians and light industrial plant maintenance staff needing a non-invasive methodology for diagnostic troubleshooting on standard 50 Hertz and 60 Hertz distribution channels. Amprobe supported this design with standardized banana-plug converter leads to maintain universal physical compatibility across diverse industrial test gear product lines.
References
- https://amprobe.com/product/a400/ – Official Amprobe legacy product documentation cataloging standard specifications, application requirements, and historical hardware configuration options for the A400 platform.
- https://www.amprobe.com/wp-content/uploads/2019/12/A400_AC-Current-Transducer_Manual.pdf – The manufacturer technical instruction manual specifying electronic tolerances, physical jaw thresholds, operating parameters, and baseline safety certifications for the instrument.