UNI-T UT251A/B/C Precision Clamp-on Leakage Current Meter

Warning!

Thank you for purchasing the UT251 series precision clamp-on leakage current meter. For full use of the product, please read the user manual carefully. Strictly observe the safety rules and notes listed in the manual. In any case, please pay attention to the safety in using the meter. Note labeled words and symbols on the panel and backboard of the meter.

• Avoid placing and storing the meter for a long time in environments with high temperature, moisture, condensation, and direct sunshine.
• Avoid strong shock on the clamp head and deformation of the iron core or fluctuation of magnetic inductivity, which will affect meter precision.
• Please replace the battery in time if its voltage is low.
• Take out the battery when the meter will not be used for a long time. Note the battery polarity when replacing the battery.
• Operation, dismantling, and maintenance of the meter shall be conducted by authorized personnel.
• Please stop using the meter and deliver it for treatment to an authorized and qualified institution if continuing usage might bring about danger.
• Note the safety symbol "⚠" in the manual and on the meter; the user shall conduct operations in accordance with instructions.
• Note the symbol "⚡" indicating extremely dangerous, in the manual; the user shall conduct operations strictly in accordance with instructions.

I. Overview

The UT251 series precision clamp-on leakage current meter is intended for measuring AC leakage current. These meters are designed by adopting state-of-the-art CT and digital integration technologies, featuring small size, high precision, and perfect function. They are widely applicable in fields such as electricity, communication, meteorology, railway, oilfield, structure, measurement, scientific research, teaching units, and mineral enterprises. The induction iron core, made of a special alloy, adopts magnetic shielding technology to avoid the impact from outside magnetic fields, assuring high precision, stability, and reliability for year-round measurement.

The meter's software, with RS232 ports, allows for online real-time monitoring and history checking, dynamic display, and maximum, minimum, and average value indication. The meter has functions such as alarm value setting, alarm indication, and reading, storing, and printing of historical data. It can also hold peak values and data, making it convenient to operate and a necessity for safety testing by electricians.

II. Difference between Types

III. Electrical Symbol

• ⚡ Extremely dangerous! Operator must strictly observe safety rules or face electric shocking, resulting in personal harm or injury and death accidents.
• ⚠ Danger! Operator must strictly observe safety rules or face electric shocking, resulting in personal harm or injury and death accidents.
• ⚠ Warning! Please strictly observe safety rules or result in personal injury or damage to equipment.
• ⛭ Double insulation
• ~ Alternative current (AC)
• ⎓ Directive current (DC)

IV. Technical Specification

V. Meter Structure

1. Clamp head
2. Meter upper cover
3. Trigger (control opening and closing)
4. Key HOLD (combination key)
5. Key POWER (combination key)
6. LCD display
7. RS232 ports, digital data could be uploaded to computer
8. Meter lower cover
9. Battery cover

Diagram showing meter structure with numbered parts.

VI. Operation Method

1. Power On/Power Off

Press the POWER key to power on; the LCD will display. Press the key again to power off. The LCD will flicker about 5 minutes after power-on, indicating automatic power-off. After 30 seconds of flickering, it will shut off to reduce battery consumption. If the POWER key is pressed when the LCD is flickering, the meter will continue working for 5 minutes. If the LCD display is dull after power-on, please replace the battery due to low battery voltage.

2. Measurement of Leakage Current and Current

⚡ Electricity, extremely dangerous! Operation shall be conducted by trained and authorized personnel. Operator must strictly observe safety rules or face electric shocking, resulting in personal harm or injury and death accidents.

⚠ Dangerous! Forbid to measure current exceeding the upper limits or face electric shocking, personal injury, or damage to equipment.

1. Turn on the power of the meter.
2. Press the trigger to open the clamp head and clamp it onto the wire under measurement. (Note: ensure the clamp head is fully closed.)

Diagram showing how to clamp onto a wire.

Diagram showing how to clamp onto two wires (live and neutral).

Diagram showing how to clamp onto a ground wire.

Diagram showing how to clamp onto a main line.

Diagram illustrating detecting power source of main lines.

Diagram illustrating detecting leakage current of wall-buried wires.

Diagram illustrating detecting safety condition of equipment operation.

Diagram illustrating detecting ground wire.

Diagram illustrating detecting power consumption of equipment leakage current.

Diagram illustrating detecting power consumption of equipment 1 leakage current.

Diagram illustrating detecting power consumption of equipment 2 leakage current.

Diagram illustrating detecting ground wire.

Diagram illustrating detecting ground wire.

3. Read the LCD display data. Displaying of the symbol "OL" means that the current of the wire under measurement exceeds the maximum upper limits of the meter. Please select a higher range meter for testing.
4. For locations that are not easy to read, please use the data hold function.
5. If the symbol "DH" appears, please release the data hold status and continue to test.

3. Peak Value Hold

Press the HOLD key for more than 3 seconds during testing until the symbol "PEHd" appears. The meter will automatically capture and display the current peak value during that time period. Release the key to return to test status.

4. Data hold, cancellation, storage, check, and deletion

1. Press the HOLD key for no more than 3 seconds during testing until the symbol "DH" appears. The meter holds the present data and stores it with automatic numbering. Press the key again to cancel hold; the meter will continue to measure. If storage data has reached 99 groups, pressing the HOLD key will display the symbol "FULL", indicating that the storage data is full. Press the HOLD key to cancel the flickering of "FULL" and return to measurement mode.
2. Press HOLD key + POWER key to enter data check mode and display the first group of data. Press the HOLD key to check storage data in a cycle. If no storage data is displayed ("null"), press the POWER key to return to data check mode.
3. Enter data check mode, then press the HOLD key for more than 3 seconds to delete all storage data. When the meter displays the symbol "DEL", indicating deletion is finished, it will automatically return to test status.

VII. Quick Check for Function

VIII. Display Examples

1. Leakage current being measured is 0.25mA.
   AC 0.25mA
2. Low battery voltage, please replace battery.
   AC 6.30mA ?
3. Leakage current being measured is 5.00mA. Measurement data hold. Automatic storage as group 03 data.
   AC 5.00mA
   03
4. Check the storage data group 03.
   AC 5.00mA

IX. Battery Replacement

⚠ Warning! Do not test with the battery cover uncovered, as it is dangerous. Note the battery polarity or you may damage the meter.

• If the battery voltage is low, please replace it.
• Please take out the battery when the meter will not be used for a long time.

1. When the battery voltage is insufficient, the meter will display the battery low voltage symbol "?", and you should replace the battery.
2. Press the POWER key to power off, confirm the meter is under power-off status, and open the battery cover to replace it with a new, qualified battery, noting the battery model. Then, close the battery cover.

X. Packing List

UNI-T TECHNOLOGY (CHINA) CO., LTD.
No.6, Gong Ye Bei 1st Road,
Songshan Lake National High-Tech Industrial Development Zone, Dongguan City,
Guangdong Province, China
Tel: (86-769) 8572 3888
http://www.uni-trend.com