IP Ratings for Sealed Enclosures

IP ratings are codes that describe the degree of protection that a sealed enclosure provides. These ratings begin with the letters “IP” for Ingress Protection and contain two digits.

• The first digit describes the degree of protection from solids.
• The second digit describes the degree of protection from liquids.

For example, the 6 in an IP67 rating denotes full protection against dust and the 7 denotes protection against full immersion for up to 30 minutes at depths between 15 cm and 1 m.

Sometimes, the letter X is used instead of a digit to indicate the absence of test data. For example, an IP6X rating denotes full protection against dust and an absence of test data for liquid protection. If an IP rating ends in a letter, however, the trailing letter indicates an additional form of protection. For example, the F in an IP67F rating indicates IP67 performance plus oil resistance.

IP ratings for electrical and electronic enclosures are defined in IEC 60509, a standard from the International Electrotechnical Commission (IEC). EN 60529 and BS EN 60529 are European and British equivalents, respectively. This article explains what IP ratings mean and how Stockwell Elastomerics provides silicone rubber for sealing out dust and/or liquids in housings, or enclosures.

IP Ratings and Soft Silicones

Silicone rubber is available in soft, low durometers such as solid sheets that measure 10 or 20 on the Shore A scale. Closed cell silicone sponge is available in even lower durometers. For sealing out dust and liquids, these soft silicone grades are preferred because they conform easily to enclosure variations, absorb tolerance stacks, and provide sealing under low clamping forces.

For plastic enclosures and thin metal housings, high clamping forces can cause deformation under load, a problem that creates unintended points of ingress for dust and/or liquids. In addition to supporting lower clamp forces, soft silicone rubber can be molded into enclosure gaskets or cut from sheets. Silicones are also inherently ozone and UV resistant with support for a wide range of operating temperatures.

• At low temperatures, silicones remain compliant and functional below the glass transition point of other elastomers.
• At higher temperatures, silicones resist compression set and stress relaxation that would cause other elastomers to experience compression set or permanent deformation.

Stockwell Elastomerics also offers soft silicone rubber that is UL94HB flame-rated or electrically-conductive grades for EMI attentuation. Although Stockwell specializes in silicone materials and gaskets for IP67 enclosures, we can provide you with silicone materials and components for IP ratings that range from IP50 to IP69. The following sections explain what these specific IP ratings mean in greater detail.

IP Ratings: Second Digit Explained

The second digit of an IP rating describes the degree of protection from water in the form of moisture or a moving liquid. IP water protection can be against condensation, direct sprays, low pressure or high pressure jets, splashing water with an oscillating spray, or full or extended immersion. Stockwell Elastomerics also provides silicone rubber for water sealing.

IP Ratings, Silicone Gaskets, and Enclosure Design

For engineers, it’s important to remember that IP ratings apply to the entire enclosure rather than to just the silicone rubber that is used for enclosure sealing. Although silicone materials and silicone gaskets are capable of achieving specific IP ratings, the enclosure material is also an important consideration. For example, if an enclosure was made of cardboard instead of metal or plastic, an IP67 capable gasket would not provide good sealing against immersion in water.

Engineers also need to consider than an IP rating is not like a material specification. Depending on the application, design considerations may include bolt torque and spacing, percent deflection, burst pressure, material thickness, and part tolerances.

Additionally, IP ratings do not discuss testing time or time dependent mechanical properties. Potential life span of the material is something that also needs to be considered. Properties like compression set or stress relaxation can adversely affect sealability over time due to material properties. View more details about stress relaxation and compression set.  Good news is that silicone, urethane foam, and fluorosilicone excel at those properties.

Appendix: IP Ratings Reference Chart