What Does a UL 94 Rating Actually Mean?
UL 94 is a materials standard, not a certification for a finished connector. It measures how a specific plastic — at a specific thickness, in a specific color — behaves when exposed to flame: whether it keeps burning, how fast, whether it drips while burning, and whether those drips are still on fire when they land. A housing resin doesn't just "have" a UL 94 rating in the abstract; the rating is only valid for the thickness and color actually tested, which is why a datasheet listing "UL 94 V-0" without a thickness is missing the detail that actually matters for a thin-wall connector housing.
Source: Underwriters Laboratories — ANSI/CAN/UL 94, Standard for Safety of Flammability of Plastic Materials for Parts in Devices and Appliances. This page is a plain-language overview; the current official test standard is the authority, not this summary.
The UL 94 Flammability Classifications
From least to most flame-resistant:
- HB (horizontal): Self-extinguishes before a 100mm mark, or burns slower than 40mm/min (3–13mm thick) or 75mm/min (under 3mm) — the least demanding classification.
- V-2 (vertical): Each specimen's afterflame stops within 30 seconds; flaming drips are allowed, and those drips are allowed to ignite a cotton indicator below the sample.
- V-1 (vertical): Same 30-second afterflame limit as V-2, but flaming drips are not allowed to ignite the cotton indicator.
- V-0 (vertical): Each specimen's afterflame stops within 10 seconds (50 seconds total across a full specimen set); no flaming drips allowed to ignite the cotton indicator.
- 5VB (vertical, larger flame): Survives a larger, more severe flame exposure than the V-tests; burn-through of the test plaque is allowed.
- 5VA (vertical, larger flame): Same severe-flame exposure as 5VB, but no burn-through of the plaque is allowed — the highest classification.
V-0 is the rating most connector housings target, and it's the one most commonly listed on connector datasheets — but per the point above, it's only meaningful alongside the thickness it was tested at.
UL 94 vs. Glow-Wire Testing (IEC 60695-2): Not the Same Thing
This is the mix-up worth catching before it causes a sourcing problem, especially for a global BOM. UL 94 tests a material's reaction to open flame — direct fire contact from a burner. Glow-wire testing (IEC 60695-2-10 through -13) tests a completely different failure mode: a glowing-hot wire loop (typically 550–960°C depending on the test tier) pressed against the material to simulate a fault condition inside the device — an overheating connection or a failing resistor — rather than an external fire.
The practical difference: North American specs and datasheets lean on UL 94 ratings; European and many Asian specs call out glow-wire performance (often alongside CTI, comparative tracking index, for tracking/arcing resistance) instead or in addition. A connector housing resin can be well-characterized for one and never tested for the other. If a design is sourced for global markets, or if a customer's spec calls out glow-wire or CTI requirements, a UL 94 V-0 rating alone doesn't answer that question — it's a different test measuring a different hazard.
Connector-Specific Compliance Checklist
- Specific thickness: get the thickness the housing's UL 94 rating was tested at — not just the rating itself. A resin can be genuinely V-0 at 1.5mm and fail to hold that rating at 0.8mm, which matters directly for thin-wall miniature connector housings.
- Color/pigment: check the color the rating applies to. Some flame-retardant formulations lose rating performance with certain colorants or masterbatches — a housing rated V-0 in black isn't automatically V-0 in every color a supplier offers.
- Glow-wire / CTI data: ask whether this exists separately, if the application or customer spec requires it — don't assume a UL 94 rating implies either.
- UL Yellow Card: confirm the rating comes from the material supplier's UL Yellow Card (or an equivalent verifiable UL file), not just a molder's or distributor's claim repeated on a datasheet.
- Finished-part testing: for a safety-critical or regulated end application, check whether the finished part (not just the raw resin) has been separately evaluated — wall thickness, ribs, and gate location in the actual molded housing can behave differently from a flat test plaque of the same material.
How Do I Select a UL 94-Rated Connector Housing?
Start with what the application actually requires — most general-purpose electronic connector housings target V-0, but confirm whether the end product's own safety standard (an appliance, automotive, or medical spec, for instance) calls for a different rating, or for 5VA/5VB in a higher-energy application. Then get the resin's UL Yellow Card reference and check the tested thickness and color against your actual part design, not just the headline rating.
If the design is going to markets or customers that require glow-wire or CTI data, ask for that separately — it won't be on the same test report as the UL 94 rating. Finally, if the connector will see any real fire-risk exposure in service (as opposed to being a component inside an already-enclosed device), verify whether finished-part-level testing exists, rather than relying on the raw material rating alone.
Where to Go Deeper
This page covers UL 94 generally — for other standards in this section, see the OCP/ORV3 Compliance Requirements Checklist, the RoHS & REACH Compliance Guide, and the MIL-DTL-38999 Connector Series Guide.
Disclaimer
General guidance only. This page is an informational overview of UL 94 as it generally applies to connector housing materials — it is not a substitute for reviewing the current UL 94 standard directly, or the specific UL Yellow Card for any material being evaluated.
Not affiliated. connectorselection.com is not affiliated with, endorsed by, or acting on behalf of Underwriters Laboratories (UL). UL and UL 94 are marks/references of Underwriters Laboratories Inc.
Not a substitute for verification. A UL 94 rating is specific to a tested thickness, color, and material formulation. Always verify the rating actually claimed applies to the specific part, thickness, and color being sourced — via the supplier's UL Yellow Card or equivalent — before making a sourcing, design, or safety-compliance decision.