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Types of Transformer Enclosures

Transformer enclosures protect transformers from the elements and users from the transformer. Learn what transformer enclosure you need for your project.

September 25, 2023

Low voltage dry type transformer

Electrical transformers are essential in keeping any commercial or industrial operation running, and transformer enclosures are a key part of protecting those transformers from the elements. Transformer enclosures also protect end users and anyone else who comes in contact with the transformer from accidental contact with live components. There are many different types of transformer enclosures: in this article we’ll cover the most common enclosures for dry-type transformers.

What is a transformer enclosure?

A transformer enclosure is the cabinet or housing over the core and coil that protects a transformer from the environment and personnel from the transformer.

What are transformer enclosures made of?

Transformer enclosures are usually constructed of mild or stainless steel. Depending on the application, different grades of steel may be used (12 gauge, 14 gauge, etc.). Which enclosure you choose will largely be dependent on the environmental conditions that your transformer must withstand. Will there be dust and dirt blowing around? What about regular rain, sleet, or snow? Will you need to wash down the transformer with a hose? Some enclosures protect against all of these conditions, whereas others are more specialized in the protection they offer. The type and location of the enclosure will determine the maintenance required for the transformer.

Dry-Type Transformer Enclosures

For dry-type transformers, there are several different NEMA ratings designating the level of protection from environmental conditions, such as rain, dust, or snow. Some enclosures are only suited for indoor use, others can be used either indoors or outdoors.

Guide to transformer NEMA enclosure types

All dry-type transformer enclosures, regardless of their NEMA rating, provide protection against any accidental contact with hazardous live parts.  Here’s a brief summary of the different NEMA enclosure types available for dry-type transformers, with examples of some suitable applications for each type:

Protection Against NEMA 1 NEMA 3R NEMA 3RX NEMA 4 NEMA 4X
Incidental contact X X X X X
Falling dirt X X X X X
Circulating dust X X
Settling airborne dust X X
Windblown dust X X X X
Light splashing water X X X X
Hosedown & splashing water X X
Rain, snow, & sleet X X X X
Corrosion X X


(Indoor use)

The NEMA 1 enclosure type protects the transformer against ingress of dirt or debris. Due to the lack of rain shields, a NEMA 1 enclosure is limited to indoor use. It is often used inside factories, commercial buildings, and machine shops. Because the enclosure is not tamper proof, it should be located away from areas with frequent public access.

A NEMA 1 transformer enclosure for a low voltage dry-type transformer


(Indoor or outdoor use)

The NEMA 3R enclosure offers the same protection features as the NEMA 1 type with the addition of guarding against rain, sleet, and snow. These additional features make it an ideal choice for outdoor applications, but it may also be used indoors just as easily as a NEMA 1. Due to its ventilated design, it will not offer adequate protection against heavy windblown dust. If the enclosure is installed where rodents and insects are an issue, a rodent screen can be added to cover the ventilated openings for additional protection.

A NEMA 3R transformer enclosure for a low voltage dry-type transformer.


(Indoor or outdoor use, corrosion protection)

The NEMA 3RX provides the same protections as the NEMA 3R, with additional protection against corrosion. For NEMA 3RX options, the enclosure will be made from stainless steel rather than mild steel to accomplish the requirement for additional corrosion protection. This type of unit is often used in moist environments where a mild steel enclosure might rust and experience premature degradation. The stainless steel design makes the 3RX ideal for areas in close proximity to chemicals and corrosive agents. Examples where this enclosure may be found would include inside chemical plants or excessively humid and moist environments.


(Indoor or outdoor use, non-ventilated)

NEMA 4 enclosures are non-ventilated, so for cooling purposes, additional space is required around the transformer core and coil for proper heat dissipation. As a result, a NEMA4 enclosure will be much larger than a typical NEMA 3R type, which also will increase the overall unit cost and space required for installation. A NEMA 4 enclosure is suitable for outdoor applications where the transformer may be exposed to splashing water or hose-directed water. A NEMA 4 enclosure can also be used in dusty environments indoors or outdoors to protect against windblown dust and flying debris.

A NEMA 4 transformer enclosure for a low voltage dry-type transformer


(Indoor or outdoor use, non-ventilated, corrosion protection)

The NEMA 4X enclosure offers the same protective features as the NEMA 4 with the addition of added corrosion resistance. Like the NEMA 3RX option, the 4X enclosure utilizes stainless steel instead of mild steel. With a NEMA 4X enclosure, the transformer is protected against windblown dust and dirt, rain, snow, sleet, and ice formation, as well as splashing and hose-directed water. The enclosure is also sealed against corrosion and corrosive liquids that may damage the unit. A totally enclosed non-ventilated corrosion resistant enclosure is most suitable for applications where the enclosure would come into frequent contact with liquids or vapors that would damage a typical mild steel enclosure. A NEMA 4X enclosure would commonly be found inside or outside some chemical plants and in coastal applications requiring protection against moisture and salt.


Transformer enclosures are vital in ensuring the proper operation of the transformer as well as the safety of its users. If you’re wondering what transformer enclosure you need, drop us a line! We have thousands of transformers in stock, suitable for all kinds of applications and environments.

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