1. Introduction
The UNI-T UT251A+ series clamp-on leakage current meters are designed for precise measurement of AC leakage current and general AC current. Utilizing unique CT technology, digital integration, and magnetic shielding, these meters offer high accuracy, stability, and reliability, with minimal interference from external electromagnetic fields.
Key features include True RMS measurement, filtering capabilities, max/min/average value display, harmonic analysis, and distortion rate testing. They can measure currents within a frequency range of 40Hz to 1kHz. Additional functionalities include LCD backlight, flashlight, data hold, and Bluetooth communication. Powered by a rechargeable high-capacity lithium battery, the UT251A+ is an essential tool for electrical safety detection in various applications such as power systems, telecommunications, meteorology, railways, oil fields, construction, metrology, scientific research, and industrial environments.
2. Safety Information
Please read this user manual thoroughly and adhere to all operating precautions before use.
- Danger! Always prioritize safety when using this meter. Operations must be performed by trained and authorized personnel. Failure to comply with safety rules may result in electric shock, personal injury, or death.
- Danger! Do not use the meter to measure circuits exceeding 600V. This may cause electric shock, personal injury, or equipment damage.
- Warning! Always ensure the clamp jaws are fully closed during leakage current and current tests.
- Position the wire as close to the center of the clamp jaws as possible for accurate readings.
- Keep the clamp jaws clean and perform regular maintenance.
- Avoid prolonged exposure to high temperatures, humidity, condensation, or direct sunlight.
- If the meter is not used for an extended period, charge it every 1-2 months to prevent battery failure.
- When replacing batteries, observe correct polarity.
- Any disassembly, repair, or maintenance must be performed by authorized personnel.
- If the meter malfunctions or poses a safety risk, discontinue use immediately and contact authorized service personnel.
- Observe all warning labels and symbols on the meter and in this manual.
3. Product Overview
3.1. Appearance Introduction
| No. | Description | No. | Description |
|---|---|---|---|
| 1 | Measuring current sensor | 6 | Power on/off, Bluetooth button |
| 2 | Clamp head opening and closing (Trigger) | 7 | Harmonic measurement button |
| 3 | Data retention, backlight button | 8 | LCD display area |
| 4 | Maximum and minimum values button | 9 | Battery compartment |
| 5 | Low pass filtering, flashlight button | 10 | Battery Cover |
3.2. LCD Display Area
| No. | Definition | No. | Definition |
|---|---|---|---|
| 1 | Battery level indicator | 7 | AC (Alternating Current) |
| 2 | AVG (Average value) | 8 | HOLD (Data hold) |
| 3 | MIN (Minimum value) | 9 | THD (Total Harmonic Distortion) |
| 4 | MAX (Maximum value) | 10 | Current value |
| 5 | BPF (Band Pass Filter) | 11 | mA (milliampere) current unit |
| 6 | Bluetooth communication indicator | 12 | Frequency value, Harmonic order |
3.3. Button Functions
| Button | Function |
|---|---|
Power | Power On/Off |
HOLD / Backlight (3s) | Short press: Data Hold; Long press (3s): Turn on/off Backlight |
MAX MIN / Flashlight (3s) | Short press: Cycle through Max, Min, Average measurement modes; Long press (3s): Turn on/off Flashlight |
LPF / Bluetooth (3s) | Short press: Toggle Low Pass Filter (LPF) on/off; Long press (3s): Turn on/off Bluetooth communication |
HARM / THD (3s) | Short press: Cycle through Harmonic orders; Long press (3s): Toggle Total Harmonic Distortion (THD) measurement |
4. Specifications
| Parameter | Specification |
|---|---|
| Power Supply | Lithium Battery DC 3.7V/1000mAh |
| Measurement Range | UT251A+: 0.00mA~300A UT252C: 0.00mA~1200A UT253C: 0.00mA~2000A |
| Measurement Accuracy | 0.00mA~999mA: ±(1.5%rdg+5dgt) 1.00A~300A: ±(1.5%rdg+5dgt) 300A~599A: ±(2.0%rdg+5dgt) 600A~1199A: ±(2.5%rdg+5dgt) 1200A~2000A: ±(2.5%rdg+5dgt) Note: Accuracy is for 40Hz~70Hz. For 71Hz~1kHz or with filter on, accuracy doubles. |
| Meter Weight (with battery) | UT251A+: ~256g (Total ~470g with accessories) UT252C: ~477g (Total ~750g with accessories) UT253C: ~664g (Total ~1160g with accessories) |
| Clamp Jaw Size | UT251A+: Φ40mm UT252C: Φ70mm UT253C: 80mm×80mm |
| Meter Dimensions | UT251A+: 192mm×96mm×40mm UT252C: 237mm×131mm×40mm UT253C: 253mm×145mm×40mm |
| LCD Size | 43mm×38mm; Display area: 36.5mm×29mm |
| LCD Backlight | Yes |
| Flashlight | Yes |
| Filter Function | Filter On: 40Hz~70Hz; Filter Off: 40Hz~1kHz |
| Harmonic Analysis | 21st order (for >10mA) |
| Distortion Rate | Yes (for >10mA) |
| Max/Min/Avg | Yes |
| Data Hold | Yes |
| Data Storage | 2000 sets (via APP) |
| Over-range Display | "OL" symbol |
| Bluetooth Communication | Yes (with APP) |
| Auto Power Off | Approximately 5 minutes after power-on |
| Sampling Rate | 2 times/second |
| Operating Current | 60mA (72mA with flashlight on) |
| Line Voltage | AC600V and below |
| Operating Environment | -10°C~50°C; ≤80%RH |
| Storage Environment | -20°C~60°C; ≤70%RH |
| Insulation Strength | AC 3700V/rms (between core and casing) |
| Safety Compliance | IEC1010-1, IEC1010-2-032, Pollution Degree 2, CAT III (600V) |
5. Setup
5.1. Battery Charging
The meter is powered by a rechargeable lithium battery. Ensure the battery is sufficiently charged before use.
- When the battery level indicator shows 1 bar or 0 bars, the battery is low. Please charge the meter promptly using the provided dedicated charger.
- If the meter will not be used for a long period, charge it every 1-2 months to prevent battery discharge and damage.
5.2. Initial Inspection
Before first use, inspect the meter and accessories for any signs of damage. Ensure all items listed in the package contents are present.
6. Operating Instructions
6.1. Measurement Principle
The leakage current measurement principle is based on electromagnetic induction. The clamp meter incorporates a toroidal current transformer composed of a metal core and windings. This transformer senses the magnetic field generated by the current or the vector sum of currents flowing through the measured conductor. The transformer then produces a current proportional to the current in the conductor, which the meter processes to calculate the corresponding leakage current.
6.2. Current Measurement
When measuring current, always try to position the measured wire in the center of the clamp jaws. If the wire deviates from the center, the error may increase by 1% to 4%.
6.2.1. Load Current Measurement
For load current measurement, clamp only one wire.
6.2.2. Leakage Current Measurement
For leakage current measurement, clamp all live and neutral wires simultaneously. This applies to single-phase two-wire, single-phase three-wire, three-phase three-wire, and three-phase four-wire systems.
6.2.3. Ground Leakage Current Measurement
For ground leakage current measurement, clamp only the ground wire.
6.3. Harmonic Measurement
Clamp the current clamp onto the corresponding live wire of the load. Press the HARM button to switch to harmonic or distortion rate test mode. Use short presses to cycle through harmonic orders (H-1 to H-20) and long press (3s) to toggle THD measurement.
6.4. Bluetooth Communication and APP Usage
The meter is equipped with built-in Bluetooth for wireless data transmission. Download the official