Introduction to UL94 Ratings
The UL94 standard, established by Underwriters Laboratories (UL), is a widely accepted test for evaluating the flammability of plastic materials used in electronic components, including connectors. These ratings ensure that materials meet safety standards, especially in environments where fire risks are a concern.
Two common ratings for connector materials are UL94V-0 and UL94V-2. Both indicate a level of flame resistance, but they differ in their performance under fire, testing requirements, and practical applications. Whether you’re an engineer, procurement specialist, or project manager, understanding these distinctions helps you make informed decisions about safety and compliance.
UL94V-0 and UL94V-2: Test Conditions, Procedure, and Attainment Criteria
To understand what sets UL94V-0 and UL94V-2 apart, let’s look at how these ratings are tested and the criteria they must meet.
Test Conditions
Before testing, materials undergo two conditioning processes to ensure consistent performance:
- Set 1: Stored at 23°C and 50% relative humidity for 48 hours.
- Set 2: Heated at 70°C for 7 days to simulate thermal stress.
This dual approach ensures the material’s flammability is reliable under both normal and harsh conditions.
Test Procedure
Both ratings use a vertical burn test:
- A specimen (typically 127 mm long, 12.7 mm wide, and of varying thickness) is held vertically.
- A 20 mm-high flame from a Bunsen burner is applied to the bottom edge for 10 seconds, then removed.
- If the material stops burning within 30 seconds, the flame is reapplied for another 10 seconds.
- A piece of cotton is placed 300 mm below to catch any falling particles and assess whether they ignite.
The test measures:
- After-flame time: How long the material burns after the flame is removed.
- Drip behavior: Whether flaming or glowing drips fall and ignite the cotton.
Attainment Criteria
Here’s how UL94V-0 and UL94V-2 differ:
- UL94V-0:
- Self-extinguishes within 10 seconds after each flame application.
- No flaming drips are allowed to ignite the cotton.
- Total after-flame time for five specimens (10 flame applications) must be ≤ 50 seconds.
- UL94V-2:
- Self-extinguishes within 30 seconds after each flame application.
- Flaming drips are permitted, as long as they don’t ignite the cotton for more than 3 seconds.
- Total after-flame time for five specimens (10 flame applications) must be ≤ 250 seconds.
Both conditioned sets must meet these standards for the material to earn its rating.
| Criteria | UL94V-0 | UL94V-2 |
|---|---|---|
| Self-Extinguishing Time | ≤ 10 seconds after each flame application | ≤ 30 seconds after each flame application |
| Flaming Drips | Not allowed to ignite cotton | Permitted, but cotton ignition ≤ 3 seconds |
| Total After-Flame Time (5 specimens, 10 applications) | ≤ 50 seconds | ≤ 250 seconds |
Price Difference Between UL94V-0 and UL94V-2
The flammability rating directly impacts the cost of connector materials, even when using the same base material like Nylon 66, a popular choice for connector housings.
- Nylon 66 UL94V-2: This is the baseline rating with minimal or no flame-retardant additives, keeping costs lower.
- Nylon 66 UL94V-0: Achieving this rating requires adding flame retardants like red phosphorus or brominated compounds, increasing the material cost by 10-20% compared to its V-2 counterpart.
The price difference stems from these additives and the processing needed to meet V-0’s stricter criteria, making it a key consideration for budgeting connector housings.
Applications and Use Cases
The right rating depends on your project’s safety and performance needs:
- UL94V-0:
- Preferred in high-safety environments such as:
- Automotive: Under-hood connectors exposed to heat and fuel.
- Aerospace: Cabin wiring with strict fire regulations.
- Industrial: Machinery control panels in hazardous settings.
- Its superior flame resistance makes it ideal where fire risks are significant.
- Preferred in high-safety environments such as:
- UL94V-2:
- Suitable for less critical applications like:
- Consumer Electronics: Household appliances or low-voltage devices.
- Office Equipment: Computer peripherals and accessories.
- It offers a cost-effective option where fire risks are minimal.
- Suitable for less critical applications like:
Impact on Connector Design and Performance
The flammability rating influences more than just safety—it affects design and functionality:
- Durability: Flame-retardant additives can slightly reduce mechanical strength or flexibility, though high-quality UL94V-0 materials are engineered to minimize this impact.
- Weight: Additives may add negligible weight, rarely a concern for connectors.
- Manufacturing: UL94V-0 materials may require more precise processing to evenly distribute additives, potentially increasing production complexity.
Choosing between UL94V-0 and UL94V-2 involves weighing these factors against your project’s priorities.