Grand Transformers Inc. is a custom designer and manufacturer of inductive components that include Power Transformers, Line / Load Reactors and DC Chokes.  GTI specializes in providing dry type custom products that meet the unique requirements of OEM's in a variety of markets, some of which include; adjustable speed drives, elevators, power quality, medical, petrochemical and instrumentation.

We are located in Grand Haven, MI and proudly offer the following product capabilities:

•  Transformers from 1KVA to 750KVA, at 5KV max voltage; Isolation, Auto, K-rated, DIT, Multipulse, Scott-T, encapsulated, single and three phase.



•  Line and Load Reactors to 1200 Arms at 5KV max voltage; power filtering inductors to 20KHz, air cores, encapsulated, single and three phase.



•  DC Chokes to 1000Adc, 360-20KHz, encapsulated.

GTI Features:

•  An experienced engineering staff


•  CSA Category certified test facility to CSA 22.2 #66, ANSI/IEC 17025 compliant


•  NIST calibrated test equipment


•  LEAN Manufacturing system


•  60 years in business

1948 - Today

GTI was established by K.C. Retzlaff in 1948.  It was operated as a proprietorship under the name of Precision Transformer located in Muskegon, MI.   In 1951 the company was moved to Grand Haven, MI and incorporated under the name Grand Transformers Inc.  As a result of K.C.'s love for amateur radio and his interest in electrical "tinkering," GTI has grown to become a World Class Manufacturer of inductive components.

In 1956, construction was started at the present Marion Street site.  Over the years, there have been numerous expansions to support the company's growth.

1973 brought in a change in management as K.C.'s two sons, Gerald and Gregory, purchased the company prior to the founder's retirement.

Over the years, GTI has purchased several magnetics companies and consolidated operations into the Grand Haven location, which expands our product offerings and customer base.

The most recent purchase was Texas Transformers in 1997. In 2003 it was consolidated into the Grand Haven facility.  The Texas acquisition increased the product range to 750KVA three phase and added several UL recognized and listed component product families.

Today, GTI is a well-known international manufacturer of custom and specialty inductive components providing products to many fortune 100 OEM's.  GTI is ISO 9001 compliant, modern and a testament to the dedicated service of our many associates, suppliers, and loyal customers.