Skip to content

To Test Delta or Wye Transformers Consider Renting a Vanguard TRM-403

 Vanguard TRM-403 Transformer Resistance Meter Transformer configuration designations like “Delta” and “Wye” originate from the way the windings are connected inside the transformer. These connections determine the way the transformer will perform, and they also determine the methods of calculation required for properly applying a given transformer.

Contact Us Now

Delta-connected transformers have the windings of three single-phase transformers connected in series with each other to form a closed circuit. The line conductors are connected to the unit where the two single-phase transformers meet. 

In a Wye configuration, three single-phase transformers are connected to a common point (neutral) via a lead from their secondaries. The other lead from each of the single-phase transformers is connected to the line conductors.

For proper testing of a Delta transformer, the Vanguard TRM-403 Transformer Resistance Meter provides reading of the phase resistance and the individual Delta winding resistance values. The Vanguard TRM-403 can also deliver the individual winding resistance values for a Wye transformer without the neutral terminal.

If the transformer winding resistance temperature is available at the time of testing, the TRM-403 is capable of calculating the equivalent resistance value at any temperature value. This useful feature can be used to compare the field readings against the factory test resistance values.

The TRM-403 can also automatically demagnetize the inductive device under test, eliminating the manual task of demagnetizing the transformer core after a resistance test.

Vanguard TRM-403 Transformer Resistance Meter specifications:


Portable transformer winding resistance meter

Physical Specifications

21”W x 17”H x 9” D (53 cm x 43 cm x 24 cm)

Weight: 35 lbs (15.8 kg)

Operating Voltage

100 ¬ 240 vac, 50/60 hz

Resistance Reading Range

1 micro-ohm ¬ 500 ohms


1 ¬ 19,999 micro-ohms: ±0.5% reading, ±1 count

20 ¬ 999 milli-ohms: ±1% reading, ±1 count

1 ¬ 2000 ohms: ±1.5% reading, ±1 count

Test Current

1A ¬ 40A in 1A increments

Test Voltage

60Vdc charging, 18V DC max during measurement

Input Channels

4 input channels for measuring resistance


Back-lit LCD Screen (240 x 128 pixels)

Viewable in bright sunlight and lowlight levels


Built-in 2.5-inch wide thermal printer

Internal Data Storage

256 static test records (each can contain up to 111 readings) and 120 dynamic test records

External Data Storage

Up to 999 test records on external USB Flash drive

Computer Interfaces

RS-232C, USB, and Bluetooth


Designed to meet UL 61010A-1 and CAN/CSA C22.2 No. 1010.1-92 standards


Operating: -10°C to +50°C (+15°F to +122°F); Storage: -30°C to +70°C (-22°F to +158°F)


90% RH @ 40°C (104°F) non-condensing


2,000 m (6,562 ft) to full safety specifications

Related electrical test equipment available for rent from Protec:

Raytech WR50-12 Two Channel Winding Resistance Test Set

Raytech WR14 15 Amp Winding Resistance Meter

Omicron CPC 100 Multi-Functional Primary Test System

This electrical test equipment is available for rent, lease, or purchase from Protec Equipment Resources. We are here to help you with your testing equipment needs.

Protec’s Calibration Lab offers accurate and affordable calibration services for all makes and models of electrical test and measurement equipment. Contact us today for a quote.

Get a Quote Today