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ST-3/XT3 Transformer Rated Wireless Site Tester

Portable 3-phase wireless watthour meter tester



The First Socket Type Transformer-Rated Site Tester

Weight: 4.5 lbs     |    Size: 6.9″ X 7.4″

Thanks to the ST-3/XT3
Big technological leaps comes in small package…

  • Revolutionary Design
  • Advanced, yet simple to use
  • WiFi Technology
  • Offers all the required tests
  • Uncompromised Accuracy

Control it from a laptop or cell phone

  • Customized configuration
  • Task Automation
  • Validation of test results at a glance
  • Export report as CSV or PDF


What else is in the bag?


  • Quick-Start Guide and User Guide
  • Factory calibration report

Hardware included:

  • 5 spares removable twist tabs
  • Adapter for 5S, 35S and 45S
  • Update Cable

Optional Accessories
(not included)

Verification Process

Speed up the process without ever compromising safety

The ST-3/XT3 is a sophisticated yet rugged tool, simple to use and controlled remotely thanks to the integrated Wifi and the Probewell Connect application. The application is offered free of charge and can be installed on your laptop, tablet or cell phone.

The Probewell Connect user interface gives you access to a complete range of tests to securely test the quality of your CT rated installations.

  • Power Quality (PQ)
  • Real-Time Waveform
  • Phasors
  • Total Harmonic Distortion
  • CT & PT Ratios
  • CT Burden
  • Admittance

Probewell | How to | ST-3/FLEX2500: Read all 3 phases simultaneously
CT Test Diagram
Probewell | How to | ST-3/PT-600: Read all 3 phases simultaneously
PT Test Diagram

Uncompromised precision

Three current sensors analyse with a typical accuracy of 0.05%.

Learn more about technical specifications >

How Does It Work?

Embedded within the ST-3/XT3, is a high performance multiphase energy metering circuitry.

This allows a full RMS and line cycle measurement of both secondary (at the meter base) and primary (with accessories) currents and voltages.

The ST3/XT3 offers elaborate test modes that can leverage such measurements to assess the Power Quality on the secondary side or perform complete transformer ratio analysis

Lightning Quick Setup!

The Form selector switch and removable twist tabs enable a toolless configuration to match any transformer rated meter base form.

You will be able to test sites with any of these CT rated meter forms:

Single-Phase: 3S and 4S

Polyphase: 5S, 6S, 8S, 9S, 35S and 45S

Fitzall™: Classe TC

Setting-up your test has never been easier; you’ll be testing in no time.

Integrated WiFi Technology

Wirelessly efficient

With built-in Wi-Fi, your tester connects wirelessly to either your laptop or device running on iOS & Android mobile.


By maximizing both your device’s camera and GPS, many manual operations are shortcut to save you valuable time.

Download the App >

Probewell | ST-3 XT3 Installation Diagram

No network, not a problem!

What if you are testing in remote areas? No network coverage is required, all test results are stored within the unit’s memory.


Its robustness, compact size and ease of operation make it an indispensable tool for testing sites in remote areas.

Leverage crucial digital insights!

Export and share test results as a PDF or CSV file.

Probewell | Probewell Connect | Export Function | CSV and PDF format
Include Probewell solutions into your daily process and make smarter data driven decisions by leverage crucial digital insights, based on sound data.

You can quickly export all your testing data in PDF or CSV format to facilitate integration with your local systems for future analysis.

Click the links below to download a sample file:

Several other tests are also available, get a sample upon request.

Technical Specification

Compatible Meters
Single-Phase 3S and 4S
Polyphase 5S*, 6S, 8S, 9S, 35S* and 45S*
*Adapter required (included)
Fitzall™ CT Rated
Compatible devices
Operating systems IOS®, Android®, Windows®
Voltage 100 – 600VAC
Working Voltage 100 – 480VAC +/- 10%
Line Frequency 58-62Hz
Bypass Circuit 20A (max for CT Rated)
Circuit Breakers 2 x 1A (press-to-reset mechanism)
Wireless 802.11b/g Access Point Only
I/O Port Full duplex for wired updates only
Update USB Cable
RMS Current ±0.05% maximum
RMS Voltage ±0.05% maximum
Frequency ±0.05% maximum
Operation Temperature -4° to 140°F (-20° to 60°C)
Storage Temperature -4° to 140°F (-20° to 60°C)
Humidity 0% to 95% (non condensing)
Physical Dimensions
Test Socket (Diam. x L) 6.5” x 7.4”
Test Socket 4.5 lb
Parts and Labor 2-years limited***
Power Quality Analysis Vrms, Irms, Frequency
Active Power (W)
Reactive Power (VAR)
Apparent Power (VA)
Power Factor
Vrms Factor
Vrms THD, Irms THD
Current Phase Angle
Voltage Phase Angle
Phase Sequence Detection
Waveform Viewer 80ms of data per channel
CT Burden 0.1, 0.2, 0.5, 1.0, 2.0, 4.0, 8.0
CT primary to secondary ratio
CT primary –˃ secondary phase
PT primary to secondary ratio
PT primary –˃ secondary phase
Deluxe Double Carrying bag Update cable
User’s manual 5 Removable Twist Tabs Plus 5 spares
Quick Start Guide Calibration report
5S, 35S, 45S adapter

(Click to expand!)