Enclosures – The First Line of Defense in Product Safety
In our ongoing Compliance 101 series, we at Product Safety Consulting, Inc. are committed to providing you with essential knowledge about product safety and certifications. Today, we’re focusing on a critical component of product design: enclosures. Whether metal or plastic, enclosures play a vital role in protecting users and internal components. Let’s dive into the key considerations for both types.
Metal Enclosures: Strength and Conductivity
Metal enclosures are prized for their durability and electromagnetic shielding properties. However, they come with their own set of compliance requirements:
1. Material Thickness: The thickness of metal enclosures depends on the specific material used. While standard thicknesses are often prescribed, manufacturers can sometimes use thinner materials if they pass equivalency testing.
2. Corrosion Protection: To ensure longevity and maintain safety, metal enclosures require https://www.3erp.com/blog/5-ways-to-make-your-metal-parts-corrosion-resistant/. This can be achieved through galvanization, painting, or other protective coatings.
3. Spacing Requirements: Typically, a minimum spacing of ½ inch is required between uninsulated live parts and a metal enclosure. When this isn’t feasible, a quick fix is to use an insulator like Kapton tape or mica can be employed to maintain insulation.
4. Earthing and Bonding: Metal enclosures must be bonded to earth ground. This is crucial for maintaining equal potential between accessible dead metal parts and earth ground. For painted surfaces, star washers are often used to break through the paint and ensure a good, low-resistance connection. Most Standards require the resistance to be less than .01ohm.
5. Sharp Edges: Many standards include a sharp edge test. Rolling the edges or deburring can bring products into compliance, enhancing both safety and user comfort.
6. Surface Temperatures: Metal enclosures have stricter temperature limits compared to plastic. Generally, these limits are 55°C for handles, 60°C for casual contact, and 70°C for surfaces known to be hot. When these limits are exceeded, caution markings may be required. Check your end product Standard for your requirements.
Plastic Enclosures: Versatility and Insulation
Plastic enclosures offer excellent design flexibility, but they must meet specific safety requirements for electrical, mechanical and thermal properties:
1. Flame Rating: The required flame rating depends on the product type and Standard. Typically, V2 rating is sufficient for portable devices, while 5V rating is necessary for permanently connected equipment. It’s important to note that several characteristics affect flame ratings – colorants and material thickness, fiberglass content and others can affect flame ratings.
2. Flame Spread: For enclosures or other polymeric parts inside your product, if surfaces are large, flame spread testing might be required.
3. Material Properties: When plastic components are in contact with uninsulated live parts, additional material properties become crucial. These include Comparative Tracking Index (CTI), Hot Wire Ignition (HWI), and High Amp Ignition (HAI). UL 746C is a reference Standard all engineers should have in their bag of tricks.
4. Alternative Materials: Full testing may not be required for using alternate materials. UL 746C provides guidelines for evaluating alternative materials in plastic enclosures.
5. Special Considerations: When enclosing Class 2 circuits, specific requirements may apply. The UL IQ Plastics database (www.ul.com) is an excellent resource for material selection and compliance information.
Conclusion:
Designing compliant enclosures is a critical aspect of product safety. Whether opting for metal or plastic, manufacturers must carefully consider material properties, protective measures, and relevant standards. At Product Safety Consulting, Inc., we’re here to guide you through these complexities, ensuring your products meet global safety and certification requirements.
Stay tuned for our next installment in the Compliance 101 series, where we’ll explore another crucial aspect of product safety and certification.