When it comes to selecting the best and safest electrical enclosure for your application, a variety of factors need to be considered. The most significant of these is the environment in which the enclosure will be used. Whether there's rain, dust, wind storms, a harsh salt water environment, or other considerations, environmental conditions are figured into the NEMA rating for enclosures and are critical to your selection. In addition, the enclosure material, size, and other factors need to be considered. This selection guide will address those to provide you with information to make an informed buying decision.
NEMA Rating
The National Electrical Manufacturer Association (NEMA) uses a standard rating system defining the types of environments in which an electrical enclosure can be used. It signifies a fixed enclosure's ability to withstand certain environmental conditions.
Following is a list of NEMA ratings and their definitions. NOTE: Those with an "X" indicate a corrosion-resistant rating that is given to enclosures made from a corrosive-resistant material, while those with an "R" indicate an enclosure that protects internal components from windblown particles. Additionally, ratings with an "S" designation indicate enclosures with an external operating mechanism which is operable even when ice-covered, and enclosures with a "K" designation indicate an enclosure constructed with knockouts (partially punched openings that can be easily removed to accommodate cables, connectors, and/or conduits).
- NEMA 1: Constructed for indoor use. The enclosure provides protection against human contact with live electrical components. They also protect the equipment from debris in the air, such as dirt and dust.
- NEMA 2: Provides the same benefits as a NEMA 1 enclosure. However, a NEMA 2 rating provides additional protection from light dripping or splashing of water (drip-proof).
- NEMA 3R and 3RX: Engineered for indoor and outdoor use, these enclosures protect against dirt, rain, sleet, and snow. They're also built to prevent ice from forming on the enclosure.
- NEMA 3 and 3X: These enclosures are rain-, sleet-, and dust-tight and are for indoor and outdoor use. They also provide added protection against dust beyond the NEMA 3R or 3RX enclosures.
- NEMA 3S and NEMA 3SX: Offer similar protection as NEMA 3, but will remain operable when covered in ice.
- NEMA 4 and NEMA 4X: Intended for indoor and outdoor use. These provide the same protections as a NEMA 3 enclosure, with added protection against water intrusion or hose-directed water.
- NEMA 5: Used indoors, it provides protection against falling dirt, settling airborne dust, and dripping, non-corrosive liquids including water
- NEMA 6 and NEMA 6P: Provide the same protection as a NEMA 4 enclosure. Additionally, these enclosures are capable of protecting the internal electrical components in temporary or prolonged water submersion up to a designated depth.
- NEMA 7: For indoor use in hazardous locations. These enclosures are explosion proof.
- NEMA 8: Offering the same protection as NEMA 7 enclosures, this enclosure can be used in indoor as well as outdoor hazardous locations.
- NEMA 9: These dust ignition-proof enclosures are for indoor use in hazardous locations.
- NEMA 10: Enclosures designed to meet MSHA (Mine Safety and Health Administration) standards.
- NEMA 12 and NEMA 12K: Intended for general-purpose indoor use. These enclosures protect against dripping and splashing water, are rust resistant, and may include knockouts (partially punched openings easily removed to accommodate cables, connectors, and/or conduits).
- NEMA 13: For general-purpose use indoors. Offer the same protection as NEMA 12 enclosures, but with enhanced protection against dripping and/or sprayed coolants and oils.
In addition to the NEMA rating, the following are some additional considerations to keep in mind when selecting the best and safest electrical enclosure.
Construction
Here are some of the materials used in the construction of NEMA enclosures along with their advantages.
- Stainless Steel: A more costly alternative, but corrosion-resistant with enhanced durability.
- Extruded Aluminum: Lighter than steel and not susceptible to rusting. Moderate price point.
- Fiberglass: Usable within a large temperature range (-31 to 300°F). Offers high chemical and moisture resistance, but is easily scratched and capable of producing toxic fumes. Has low impact resistance and can be more costly in non-corrosive locations.
- PVC Plastic: This material is sensitive to temperatures greater than 140°F and has limited thermal capacity. Other than that, it offers durability, long life cycle, high impact resistance, good insulation, is fire safe, recyclable, and resistant to UV degradation.
- ABS Plastic: The shiny surface of these enclosures is resistant to concentrated acids and alkalis as well as mineral and vegetable oils. However, it's degradable with acetone and flammable at higher temperatures. Best suited for temperatures 0 to 125°F.
- Polycarbonate Plastic: Provides high impact resistance and is usable in a broader temperature range (-31 to 180°F). Does not stand up well to exposure to alkalis or strong organic solvents, but is resistant to acidic environments. Offers strong UV stability.
- Polyester Plastic: Very lightweight, it offers moisture, chemical, and high impact resistance. Polyester plastic has excellent insulation properties, and is usable in a wide temperature range (-40 to 248°F). However, its impact resistance will be reduced in cold weather and its performance can be impacted by direct sunlight.
When determining which material to use for an enclosure, you'll want to consider the price, the weight, aesthetics, and the thermal issues of each material. Carefully selecting the correct enclosure material is important to ensure a long life for the enclosure.
Sealing Quality of the Enclosure
It's important to understand the degree to which an enclosure is sealed. It impacts the protection of internal components, and keeps components concealed and away from passers-by who might otherwise be exposed to potentially dangerous or hazardous electronics. At the minimum, select an enclosure that has protection against windblown dust. If total protection is required, select a NEMA 4 rated enclosure. If abrasive weather environments, corrosive chemicals, pollution, or poor air quality are an issue, choose a NEMA 4X stainless steel enclosure.
Enclosure Size
Enclosures are either floor mounted or free standing. When sizing, you'll need to determine the height, width, and length of the project with the components when mounted on a back panel. Once that's determined, you now have your minimum internal dimensions of the enclosure. Remember, you can always move up to a bigger size enclosure if necessary, but in the end be sure to select an enclosure properly sized for your project
Additional Options to Consider
There are a few additional things to consider for your enclosure, along with possible accessories. Will modifications be necessary to the enclosure before it's put in use? Will the surface of the structure that it's being mounted to be able to support the weight of the enclosure or will it need to be fortified? As for electrical box accessories, will you need pole mount kits, lighting, hole plugs, door locking hardware, or hinged front panels?
While understanding NEMA ratings can be a little daunting, choosing the best and safest electrical enclosure can be easier when you do some research and take time to assess just what you need. In addition to pole- or wall-mounted enclosures, Zoro also offers underground enclosures that provide aesthetic as well as functional benefits, all while keeping electrical systems and electrical junctions both accessible and out of sight.
Product Compliance and Suitability
The product statements contained in this guide are intended for general informational purposes only. Such product statements do not constitute a product recommendation or representation as to the appropriateness, accuracy, completeness, correctness or currentness of the information provided. Information provided in this guide does not replace the use by you of any manufacturer instructions, technical product manual, or other professional resource or adviser available to you. Always read, understand and follow all manufacturer instructions.