Before You Buy Connectors Interconnects: The Checklist We Use Internally

A connector costs cents; a field failure costs dollars

A connector is a few cents on a BOM full of dollar items, so it gets ordered first and questioned last. Every procurement desk knows that tension — and it is backwards. In our own buying, a wrong connector has cost us crimp rework, scrapped harnesses, and the occasional angry customer call, all of it worth more than the parts. So before any connector order leaves the desk, run the same short checklist. Here it is.

Read the electrical fine print

Start with pitch, because that is where the quiet mistakes live. JST XH is 2.5 mm; a "looks compatible" 2.54 mm header will not mate beyond two positions. Confirm pitch against the actual mating part, not the drawing. Next, current: the ratings on the datasheet are single-circuit maxima at 25 °C with a specified wire gauge. JST PH is 2 A with AWG 24; loaded in a harness at 60 °C, plan on 20–30 % less. Then voltage — PH's 100 V rating disappears next to XH's 250 V, so don't reuse a 2.0 mm part just because the 2.5 mm one is out of stock.

Plating decides dry-circuit reliability. For signal lines below about 20 V with microamp loads, tin contacts suffer fretting corrosion over years of thermal cycling — spec gold. For power lines, tin is fine and roughly a third of the price. Our rule: gold when the signal matters and the current is small, tin when it is big.

Mating cycles decide the price

Cheap connectors betray you on durability. A standard Molex Micro-Fit terminal is rated for 30 mating cycles — fine for a sealed box, useless for a user-serviceable battery compartment. The RMF variant with factory lubricant does 250. Souriau's UTS circular is rated 250 cycles; the UTG series 500; the aerospace 8STA also 500. Match cycles to how often a human will touch the joint, not to how long the product lasts. And when the product vibrates — fans, pumps, anything on a door — require a positive latch or TPA secondary lock. Friction-fit only, under vibration, is a return waiting to happen.

Environment: check the un-mated rating

IP numbers get quoted like absolutes, but they are often only true mated. If your cable end sits unplugged in a damp enclosure, you need the unmated rating: Souriau's UTS Hi-Seal variants hold IP68 even with nothing plugged in. Check salt spray hours (500 h is typical for a marine-grade part), UV stability for anything outdoors, UL94-V0 flammability as a baseline, and glow-wire compliance if the appliance standards require it. And confirm the operating temperature covers the derated load, not just survival.

Supply chain: the second question

After the engineering check comes the buying check. Is there a drop-in second source? (JST XH has one; many proprietary 2.0 mm systems do not.) What is the MOQ — and is it per part number or per line? Crimp tooling is the hidden gate: verify the terminal's die exists for the press your harness shop owns, or you will pay for manual crimping. Finally, quote the lead time before you engineer the product around a part: in 2026, commodity JST lines run 6–12 weeks, pre-terminated Molex assemblies 8–16, and anything MIL-qualified 20 weeks plus.

The checklist takes ten minutes, and it filters out most of the failures we see in the field. When your BOM is ready, run it through our BOM upload — it matches every line against current stock and lead times in one pass, which is exactly the last check you want before committing a schedule. If a part is missing or short, the search will surface the nearest alternatives.