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Transformer rated wireless site tester



The First Socket Type Transformer-Rated Site Tester

Field Testing Reimagined

  • Revolutionary Design
  • Miniaturized Hardware
  • Fully integrated
  • Enhanced User Experience
  • Uncompromised Accuracy

WEIGHT: 4.5 lbs
SIZE: 6.9″ X 7.4″


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)

Speed up your site testing

As the first socket-type site tester, the XT3 offers an enhanced user experience while quickly offering complete testing capabilities.

Power Quality (PQ)

Real-Time Waveform


Total Harmonic Distortion

CT & PT Ratios

CT Burden


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

Probewell | ST-3 XT3 Installation Diagram

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 >

Lightning Quick Setup

Fast twist & lock tab setup with minimal wiring for quick and safe operation.

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

Uncompromised accuracy

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

Learn more about technical specifications >

Highly Compatible

Easily configurable with twist & lock removable tabs, 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™: CT Rated

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

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

Click the links below to download a sample file:

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


What if I test in remote areas?

No wireless network coverage is required. All tests results are stored in the unit.


Combined with its high portability and lightning quick operation, it is the ideal companion for testing in remote areas.


Technical Specifications

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