Industrial enclosures often have to meet NEMA and IP standards for ingress protection. These aren’t the only standards designers should consider though. There’s also UL50 and UL50E. Established by Underwriters Laboratories, these were developed to ensure that electrical enclosures would be safe. Safety depends at least in part on the gasket, so there are UL standards for gasket materials too.
The UL difference
Achieving NEMA or IP certification entails passing some stringent tests. However, these tests only verify dust and water resistance. They don’t explicitly test the gasket material. UL testing does.
Gasket material is tested because environment and use affect how long it lasts. Some gaskets are exposed to UV outdoors. Others, especially if near high voltage equipment, can be attacked by ozone. Some enclosure gaskets will endure periodic recompression when the door is repeatedly opened and closed. Other are in continuous compression, as might be the case around an electronics assembly.
These variables place different demands on the gasket material. Many gaskets might hold up to NEMA and IP testing but the material could degrade slowly and reduce the protection the enclosure provides.
Gasket Material Certification
To address the impact of use and environment on enclosure performance, UL developed tests for gasket material. These are defined in UL157, “Standard for Gaskets and Seals”. This covers both foam and solid elastomeric and composite gasket materials.
Materials passing UL157 can be considered as “UL Recognized Components”. Using components certified this way in an end product simplifies the process of getting UL approval. (Other UL standards may also be applicable.)
Buy UL-Rated Gasket Material
When designing equipment, using UL-rated materials will save time and money in testing. And later, when gaskets are being replaced, it might also be prudent to stick with UL157 materials. These range from neoprene and EPDM foams to silicon and even cork. (But note that adding a pressure sensitive adhesive nullifies any prior UL rating.)
Finding the right UL-rated gasket material for a specific application can be difficult. If unsure what to use, consult a material specialist at Hennig Gasket.