Connector Housing Materials: Choosing Between PA66, PA6, and PBT

A connector housing does more than hold the contacts in place. It keeps terminals aligned during mating, provides electrical insulation between conductors and the panel, and supports the mechanical loads generated during insertion and removal.

It also has to retain its shape as the equipment heats up, resist ignition if a nearby component overheats, and remain dimensionally stable as temperature and humidity change.

No material is best at all of these jobs. Improving flame resistance, stiffness, moisture stability, or impact strength can introduce tradeoffs elsewhere. That is why the housing material and grade need to be specified deliberately rather than treated as a cosmetic detail.

UL 94 is a small-scale flammability test used to classify how plastic materials behave after exposure to a flame. Horizontal testing can produce an HB classification, while vertical testing uses ratings such as V-2, V-1, and V-0. Among those vertical classifications, V-0 has the most stringent requirements.

The point that is often missed is that a UL 94 rating is tied to a specific specimen thickness. The same resin grade may achieve V-0 at one thickness and a lower classification at another.

That matters for molded connector housings because wall thickness is rarely uniform. An inlet flange may be much thinner than the main body, and the thinner section can become the limiting condition for the finished part.

For that reason, a material callout should include both the UL 94 classification and the applicable thickness. A datasheet that simply states “V-0” without identifying the tested thickness does not provide enough information for a meaningful comparison.

IEC 60695-11-10 uses comparable horizontal and vertical burning classifications and is commonly referenced alongside UL 94 in international applications.

Current does not have to punch through plastic to cause a fault. It can creep across the surface on a wet film of dust or condensation. The leakage current carbonizes a thin path, the path conducts more, and the process runs away until a track burns across the surface. The voltage at which that track forms is the comparative tracking index.

IEC 60112 sorts materials into four groups. Group I reaches 600 V or more. Group II covers 400 to 599 V. Group IIIa covers 175 to 399 V. Group IIIb covers 100 to 174 V.

This is where flame retardants carry a cost. The additive systems that push a material to V-0, particularly halogenated systems with synergists, tend to lower the tracking index. A material can end up easier to flame retard and harder to use at working voltage on a contaminated surface. See contact cleaning and maintenance for how that surface is protected.

Nylon 66 is the material most connector housings are molded from. It is strong, with tensile strength in the 80 to 100 MPa range, and its heat deflection temperature runs 230 to 260 degrees Celsius. Flame retardant grades reach V-0, and unfilled grades often sit at V-2.

Its weakness is water. PA66 absorbs 1 to 3 percent of its weight, and the absorption changes dimensions. A housing molded and measured dry will be larger after it sits in a humid plant. Thick sections dry out slower than thin walls, so the part does not grow evenly. For a panel cutout with tight tolerance, that movement is the variable nobody planned for. Chemical resistance is good against hydrocarbons and only fair against acids and bases.

Polybutylene terephthalate absorbs 0.1 to 0.5 percent, an order of magnitude less than nylon. For a panel cutout, a latch, or a header soldered to a board, that stability is the reason to choose it.

PBT also resists acids, bases, and hydrocarbons well. Standard grades have a lower heat deflection temperature, roughly 170 to 200 degrees Celsius, and heat stabilized grades reach about 220. Tensile strength is lower, in the 50 to 70 MPa range, and the material is more brittle. Snap fit fingers that flex on every assembly are a poor match, press fit and screw fixed designs are a good one. Parts that pass through a reflow oven see peaks near 260 degrees Celsius, past what these materials survive without deforming, which is why semi aromatic grades take over in surface mount work.

Cord and housing ratings use the same scale, covered in 60 C, 90 C, and 105 C cord ratings.

Then ask for the yellow card. UL lists every recognized grade with flame class by thickness, hot wire ignition, high amp arc ignition, relative thermal index, and tracking index. It settles arguments photos of the part cannot.

• Material and grade, not the word nylon. Grade names count because two PA66 grades can carry different flame classes and different tracking indexes.
• Flame class with the thickness it applies to.
• Glow wire requirement, when IEC 60335-1 or another appliance standard applies.
• Tracking index group, matched to working voltage and pollution degree.
• Continuous temperature and the relative thermal index after long exposure.
• Color and any UV stabilizer, since pigments change flame performance and tracking resistance. Restricted substances are covered separately in RoHS and REACH compliance.