Types of Transformer Enclosures

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. If you need additional protection for the transformer windings as well as the enclosure, you may want to consider a cast-resin 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:

NEMA 1

(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.

NEMA 2

(Indoor use)

A NEMA 2 enclosure is also intended for indoor applications only. It provides the same protection as a NEMA 1 enclosure against solid objects, with the added benefit of limited moisture protection. Specifically, it is designed to protect against dripping and light splashing water. This rating does not imply protection from rain, but rather from moisture caused by condensation. Typical applications include laundry rooms or areas near HVAC equipment.

NEMA 3

(Indoor or outdoor use)

NEMA 3 enclosures are suitable for both indoor and outdoor applications. In addition to the protections provided by NEMA 2, a NEMA 3 enclosure offers improved resistance to water and dust. It is designed to protect against windblown dust, rain, sleet, and snow, often using a gasketed cover. The enclosure will also remain undamaged by ice forming on its exterior. These enclosures are commonly found on construction sites, ship docks, and in tunnels or subway systems subject to wet conditions.

NEMA 3R

(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.

NEMA 3S

(Indoor or outdoor use, operable when ice-laden)

A NEMA 3S enclosure provides the same environmental protection as a NEMA 3 enclosure, with the added requirement that external mechanisms remain operable when ice forms on the enclosure. This typically applies to doors and latches. Designs often include overhead shielding to prevent ice buildup and horizontally operating latches that continue to function even when ice is present.

NEMA 3RX

(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.

NEMA 4

(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.

NEMA 4X

(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.

NEMA 5

(Indoor use, dust protection)

NEMA 5 enclosures are intended for indoor applications and are designed primarily to keep out dust. While they do include a gasket, it is meant for dust protection rather than water intrusion. Typical environments include cement plants and steel mills. Despite the higher numerical designation, NEMA 5 does not offer greater protection than NEMA 4. In practice, most engineers specify a NEMA 4 enclosure for dusty environments, making NEMA 5 enclosures uncommon and difficult to source.

NEMA 6

(Indoor or outdoor use, temporary submersion)

A NEMA 6 enclosure includes the protections of lower NEMA ratings, including resistance to falling dirt, hose-directed water, and ice formation. In addition, it is designed to withstand temporary submersion in water. 

NEMA 6P

(Indoor or outdoor use, prolonged submersion, corrosion protection)

NEMA 6P enclosures provide all the protections of NEMA 6, with the added capability of withstanding prolonged submersion in water or oil. UL 50 defines this test as submersion at a depth of six feet for a 24-hour period, with a conduit connector installed during testing. NEMA 6P enclosures also include corrosion resistance and are commonly specified for applications such as mines, manholes, and quarries where extended but non-continuous submersion may occur.

NEMA 12

(Indoor use, dust and drip protection)

A NEMA 12 enclosure is designed to protect against the ingress of solid objects, falling dirt, settling dust, and dripping liquids. It is intended for indoor use and is often compared to NEMA 3, but without protection against outdoor weather. Instead of guarding against windblown dust, it protects against settling airborne dust, lint, and fibers. It also provides resistance to seeping oil, coolant, and light splashing water. Despite the higher number, NEMA 12 represents a relatively basic level of protection.

NEMA 13

(Indoor use, oil and coolant spray protection)

A NEMA 13 enclosure builds on the protections of NEMA 12 by adding resistance to oil and coolant splashing or spraying. Like NEMA 12, it is intended for indoor use and provides a basic level of protection despite its higher numerical designation.

Conclusion

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, fill out the form below! We have thousands of transformers in stock, suitable for all kinds of applications and environments.