Tierney Manufacturing Practices

Transformers are manufactured under conditions which promote high-quality workmanship. Rigid quality control, along with our conservative "industrial type" designs, assures the user of many years of trouble-free service.


Tierney air-cooled transformers, both enclosed type and open-design core-and-coil type, are manufactured to meet or exceed all current applicable standards of ANSI, IEEE, NEMA and U.L. All transformers pass ANSI routine tests prior to shipment from the factory.

Tierney Transformers are Underwriters Laboratories listed and built to the following specifications.

Core Construction

The electrical steel used in Tierney air-cooled transformers is of the highest-quality grain-oriented, non-aging type silicon-steel, with a superior surface insulation.


This steel, together with our method of burr-less shearing and jig-stacking, results in an efficient transformer core which is low in losses, exciting current and inherent noise level.


Rigid steel angles and channels, together with tie bolts insulated from the core, securely clamp the magnetic structure and support the coils.

Coil Construction

All Tierney transformers are carefully hand-wound with copper magnet wire only.


Class 105 and Class 180 coils utilize heavy film magnet wire insulation or DuPont Nomex* wrap insulation.


Class 220 coils are wound with magnet wire with HML film or DuPont Nomex* wrap insulation.


Layer and ground insulation consists of DuPont Nomex* or equivalent. Duct spacers are high-temperature fiberglass reinforced glass sticks.


All coils receive a final wrap of half-lapped unimpregnated glass tape.


After dipping in a high quality varnish, the entire core and coil is baked. The end result is a transformer with coils securely bonded and braced to resist possible winding displacement due to voltage surges and stress from external sources.


Taps are normally on the high voltage winding, formed in a loop out of the magnet wire.


*DuPont Registered Trademark

Enclosure Construction

Indoor enclosures are constructed of 14 GA. steel finished with a high quality grey primer and enamel.


Outdoor enclosures are constructed of 12 GA. steel finished with a high quality zinc coating, then primer, and finally a coat of urethane or epoxy finish.


Outdoor Enclosures are also available in galvinized or stainless steel. Consult factory for pricing.


Core and coils are specially assembled and mounted in the enclosure on Neoprene pads to provide excellent below normal sound levels.