Electrical enclosures are usually sealed by one of four types of gaskets – strip, die-cut, form-in-place and bulb extrusion.
Gaskets help to seal electrical enclosures according to the requirements of the National Electrical Manufacturer’s Association (NEMA): Ratings are numbered from 1 to 12. Most common ratings for indoor applications are 12 and 13 while 3, 4, 4x, 6, and 6P are most common for outdoor applications.
Electrical enclosure standards are important because they directly affect safety and protection, as well as help you select and obtain the proper product for your needs.
Images courtesy of SFS Manufacturing, and Alpine Elastomer Products
Gasket design in an enclosure is as critical in forming a good seal as the gasketing material itself. Design will have a significant effect on functionality, aesthetics, and overall performance.
Common gasket types include:
- Stripping – supplied in rolls of material slit to a specified width that can be cut to length by the assembler. Low scrap-rate makes stripping cost-effective; however, corner seams may make the system susceptible to wear and leakage if not properly designed and assembled.
- Die-cut – whether the material is cut with a steel-rule die, water-jet, or laser, die cutting eliminates corner seams. Die-cut gaskets are most common when the complexity of the design does not allow for stripping or when the overall size does not result in large center scrap that can be minimized by designing a “fold-out” gasket.
- Form-In-Place – dispensing equipment is used to apply an elastomer in liquid form directly into an enclosure. This liquid then foams and cures at room temperature. Form-in-place, typically inexpensive to apply, is most beneficial when the gasket design is very complex or would result in significant yield loss with a die-cut.
- Bulb Extrusions – extrusions can be tailored for abrasion and/or environmental resistance by using very durable elastomers. The hollow center allows for compressibility, as the material may be naturally firm. The skinned surface on all sides, combined with a high density, minimizes any water ingress.
Gaskets can be designed into an enclosure using various techniques:
- Channeling a gasket in a specified position can prevent sliding or moving over time
- Flat, blade, and angled flanges offer specific performance advantages and can affect sealing surface area and compression force
- Shields and flanges can be designed to protect a gasket from physical damage, UV, and chemical exposure
- Bolts or hinges can be designed to eliminate surface bowing
- Maximizing gasket wall width helps reduce ingress
- Avoid stretching a gasket, as it can lead to displacement over time
- When possible, design around material thickness and grade, making sure to consider the gap tolerance range
By knowing what type of seal works best in your electrical enclosure upfront, you could save a whole lot on the back end – especially if your enclosure is going to be used in extreme weather conditions. Look at the different types of seals before making a purchase. That way you provide the best protection possible for your electrical enclosure’s contents and you protect your investment.