The consequences of such accidental exposure can be tragic. According to statistics collected and published by Capelli-Schellpfeffer, Inc., electrical accidents called arc flashes kill one or two people in the United States every day. Many more are injured and then there is the cost of damaged equipment and lost production to consider. Numerous standards have been devised to reduce the frequency of such accidents and make industrial environments as safe as possible. These standards govern every aspect of equipment and procedures used for managing electricity. For example, IEC 60529 classifies the level of protection provided against accidental contact with live electrical parts and the intrusion of solid objects (including tools and body parts like hands and fingers), dust, and water in electrical enclosures.
However, there is more to adhering to safety standards than including them as requirements in an RFP. You have to know what they mean so you can select the right equipment for the right task and enforce their use. And that can be a challenge as you have to understand what the different ratings mean and how they are applied in your particular environment. In the case of IEC 60529 the grading is called an IP rating.
“IP is short for Ingress Protection, and is specifically oriented to the amount of security an electrical cabinet has against the intrusion of either solid objects, dust or moisture,” says John Kovacik, Principal Engineer, industrial control equipment with Underwriters Laboratories Inc. Underwriters Laboratories is an independent product safety certification organization that has been testing products and writing safety standards for more than a century. “The IP rating is very important for knowing what kind of enclosure is appropriate for your particular environment and application.”
An IP rating consists of the letters IP followed by two numbers and an optional letter. The numbers provide a grading against a set of conditions – specifically delineating the level of protection an enclosure has against the penetration of solids and dust (first number) or liquids (second number). If a cabinet has no rating against one of these categories of penetration, the number is replaced with an X. For example, an electrical socket rated IP22 is protected against the insertion of fingers and will continue to function safely when exposed to vertically or nearly vertically dripping water. IP22 or IP2X are typical minimum requirements for the design of electrical accessories for indoor use.
“IP ratings are very important to people setting up equipment in almost any environment,” says Kovacik, who adds that enclosures are further categorized by the environments they are designed for. “If you are setting up an electrical cabinet in an outdoor environment in Alaska, you need to know the enclosure you purchase can withstand severe winter conditions. Buying an enclosure engineered for an indoor SMT line won’t satisfy your needs. These ratings help you determine what type of enclosure is right for your requirements.”
Solids
| First Number | Object size protected against | Effective against |
| 0 | — | No protection against contact and ingress of objects |
| 1 | >50 mm | Any large surface of the body, such as the back of a hand, but no protection against deliberate contact with a body part |
| 2 | >12.5 mm | Fingers or similar objects |
| 3 | >2.5 mm | Tools, thick wires, etc. |
| 4 | >1 mm | Most wires, screws, etc. |
| 5 | Dust protected | Ingress of dust is not entirely prevented, but it must not enter in sufficient quantity to interfere with the satisfactory operation of the equipment; complete protection against contact |
| 6 | Dust tight | No ingress of dust; complete protection against contact |
Liquids
| Second Number | Protected against | Details |
| 0 | Not protected | — |
| 1 | Dripping water | Dripping water (vertically falling drops) shall have no harmful effect. |
| 2 | Dripping water when tilted up to 15° | Vertically dripping water shall have no harmful effect when the enclosure is tilted at an angle up to 15° from its normal position. |
| 3 | Spraying water | Water falling as a spray at any angle up to 60° from the vertical shall have no harmful effect. |
| 4 | Splashing water | Water splashing against the enclosure from any direction shall have no harmful effect. |
| 5 | Water jets | Water projected by a nozzle against enclosure from any direction shall have no harmful effects. |
| 6 | Powerful water jets | Water projected in powerful jets against the enclosure from any direction shall have no harmful effects. |
| 7 | Immersion up to 1 m | Ingress of water in harmful quantity shall not be possible when the enclosure is immersed in water under defined conditions of pressure and time (up to 1 m of submersion). |
| 8 | Immersion beyond 1 m | The equipment is suitable for continuous immersion in water under conditions which shall be specified by the manufacturer. Normally, this will mean that the equipment is hermetically sealed. However, with certain types of equipment, it can mean that water can enter but only in such a manner that produces no harmful effects. |
Further complicating matters is the fact that the IEC isn’t the only organization that offers a rating system for electrical enclosures. The National Electrical Manufacturers Association (NEMA) also has a system of protection ratings. While you may find an IP rating on almost any piece of electrical equipment, NEMA ratings are specifically focused on the industrial environment and are predominantly North American.
According to Kovacik, NEMA ratings cover additional qualifications not addressed by the IEC standards so they don’t map directly to IP ratings and that makes it important to understand how they relate. NEMA ratings also address issues such as corrosion resistance and construction practices which are not addressed by IP ratings. Because NEMA covers these additional factors, NEMA and IP ratings are not truly equivalent. A NEMA rating can satisfy or exceed all the requirements of an IP rating – for example, NEMA 1 meets all the requirements of IP20 and NEMA 6 meets all the requirements of IP67 – but the reverse is not true.
NEMA Ratings:
| Type Designation | Effective against |
| 1 | Indoor use primarily to provide a degree of protection against limited amounts of falling dirt. |
| 2 | Indoor use primarily to provide a degree of protection against limited amounts of falling water and dirt. |
| 3 | Outdoor use primarily to provide a degree of protection against rain, sleet, wind blown dust and damage from external ice formation. |
| 3R | Outdoor use primarily to provide a degree of protection against rain, sleet, and damage from external ice formation. |
| 3S | Outdoor use primarily to provide a degree of protection against rain, sleet, windblown dust and to provide for operation of external mechanisms when ice laden. |
| 4 | Indoor or outdoor use primarily to provide a degree of protection against windblown dust and rain, splashing water, hose-directed water and damage from external ice formation. |
| 4X | Indoor or outdoor use primarily to provide a degree of protection against corrosion, windblown dust and rain, splashing water, hose-directed water, and damage from external ice formation. |
| 5 | Indoor use primarily to provide a degree of protection against settling airborne dust, falling dirt, and dripping noncorrosive liquids. |
| 6 | Indoor or outdoor use primarily to provide a degree of protection again hose-directed water, and the entry of water during occasional temporary submersion at a limited depth and damage from external ice formation. |
| 6P | Indoor or outdoor use primarily to provide a degree of protection against hose-directed water, the entry of water during prolonged submersion at a limited depth and damage from external ice formation. |
| 7 | Indoor use in locations classified as Class I, Division 1, Groups A, B, C or D hazardous locations as defined in the National Electric Code (NFPA 70) (Commonly referred to as explosion-proof). |
| 8 | Indoor or outdoor use in locations classified as Class I, Division 2, Groups A, B, C or D hazardous locations as defined in the National Electric Code (NFPA 70) (commonly referred to as oil immersed). |
| 9 | Indoor use in locations classified as Class II, Division 1, Groups E, F and G hazardous locations as defined in the National Electric Code (NFPA 70) (commonly referred to as dust-ignition proof). |
| 10 | Intended to meet the applicable requirements of the Mine Safety and Health Administration (MSHA). |
| 12/K | Indoor use primarily to provide a degree of protection against circulating dust, falling dirt, and dripping noncorrosive liquids. |
| 13 | Indoor use primarily to provide a degree of protection against dust, spraying of water, oil, and noncorrosive coolant. |
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