MTO300 series

Automated six-winding transformer ohmmeters

  • Automated eight-terminal/six-winding measurement capability
  • Interchangeable lead set with the Megger three-phase series of TTRs
  • Simultaneous winding magnetization for fast and accurate DC winding resistance measurements of high inductive loads
  • Tests operation of on-load tap changers
  • Built-in auto-demagnetization feature
  • Automatic discharge
  • One-time connection principle results in a 4x faster setup time

The MTO300 series of automated six-winding transformer ohmmeters delivers full eight-terminal/six-winding resistance measurement capability. It's designed to save you time by testing all normal six windings without having to disconnect and reconnect leads during testing. Also, the simultaneous winding magnetization (SWM) method gives fast and reliable measurements, even on large transformers with delta configuration on the low voltage side.

Additionally, the MTO300 series leads are interchangeable with the Megger TTR300 series of three-phase turns ratio instruments, eliminating additional connecting time for turns ratio measurements. So, if you need to test both turns ratio and winding resistance, you can save time and money since only one lead set is needed to connect to the transformer.

The series consists of the MTO300 and the MTO330A:

  • The MTO300 base model is designed to be remote controlled via PowerDB software on an external PC or a Megger transformer test product with on-board computer.
  • The MTO330A offers the same functionality as the MTO300 but is equipped with an industrial grade, 12-inch touch controller. The display is designed to operate in direct sunlight (1600 nits brightness), and all the components are rated to operate from -20 °C to +50 °C. An additional feature that has been added to the MTO330A is the “safety shutdown” which automatically saves results and properly shuts controller down in the event of an abrupt power disruption.
Technical Documents
Technical guide
Guide to transformer winding resistance measurements
Technical guide
Transformer Tap Changer Testing
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Transformer Test Instrument Software Updates for TTR330A, MTO330A, MWA330A, DELTA4310A

The following components have been updated:

PowerDB ________________ V11.2.10 

MTOTestXP ______________ 2019.12.03.1

Delta Manual Control ______________   

Instrument Config ______ 1.0.20023.1919

Splash Screen __________ 1.0.21075.830

Factory Config _________ 1.0.21122.850

Megger Update Manager __ 1.0.21165.1032



- Megger recommends that you return your instrument annually for calibration verification.
- Any instrument returned for re-calibration will be updated with the latest firmware and software versions.
- Certified Factory Calibration is valid for one year.


Incorrect installation of updates or incomplete updates may cause the equipment to become unusable.

If damage occurs from improper updates, the customer may be responsible for repair costs.

Software updates for TTR330A, MTO330A, MWA330A and DELTA4310A

Download this zip file, extract, and run the executable.


256bit Hash:

763 MB | 02/08/2022
745.9 MB | 09/08/22
Update Instructions

Please download and read these instructions before performing the update.


623.9 KB | 09/08/22