How to Select a Connector: Pitch, Current Rating, and Environment

How to Select a Connector: Pitch, Current Rating, and Environment

Connectors look simple, but in real products they’re a top cause of failures: intermittent power, random resets, broken ports, loose cables, corrosion, vibration issues, and high warranty returns.

If you choose connectors using only “it fits the PCB footprint,” you’ll get burned.

This guide explains how to select connectors correctly—based on pitch, current rating, voltage, environment, mechanical life, and manufacturability.

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Step 1: First decide the connector “job”

Before picking a part number, answer:
• Is it power, signal, or data?
• Is it internal (inside the product) or external (customer plugs/unplugs)?
• Is it board-to-wire, board-to-board, or cable-to-cable?
• Is it used once (factory assembly) or used often (end-user)?
• Will it face vibration, moisture, dust, heat, or chemicals?

These answers decide almost everything.

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1) Pitch (spacing): how to pick it

Pitch is the distance between pins (example: 2.54mm, 2.0mm, 1.25mm).

Common pitches and typical uses
• 2.54mm: classic headers, prototypes, easy manual assembly
• 2.0mm: compact board connectors, decent current, common in products
• 1.25mm / 1.0mm: compact consumer devices, smaller current, more delicate
• 0.5mm / 0.4mm: fine-pitch board-to-board and FPC connectors (high density)

How to choose pitch:
• If you need high current and ruggedness, go bigger pitch
• If you need compact size, go smaller pitch
• If you expect field handling (people plugging), avoid extremely tiny pitch unless necessary

Common mistake:
Choosing too small a pitch for real current → heat, contact wear, voltage drop.

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2) Current rating (and why it’s often misleading)

Connector current ratings are not universal. They depend on:
• number of pins carrying current
• ambient temperature
• airflow
• wire gauge
• mating cycles and contact condition

Practical selection rules
• Never run at the connector’s rated current with zero margin.
• For power connectors, use at least 50% margin when possible.
• Check the wire gauge and crimp contact current rating too (not just the housing).

Example:
A connector rated 3A/pin may only handle that with thick wire and good cooling. In a sealed box at 60°C, it may not.

Common mistake:
One connector pin carrying high current and heating the plastic housing over time.

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3) Voltage rating and creepage/clearance

For low voltage (5V/12V/24V), voltage rating rarely limits you—but for higher voltage (48V, mains), it becomes critical.

Check:
• connector voltage rating
• creepage/clearance on the PCB
• insulation material rating

Common mistake:
Using a connector that “works in lab” but fails safety compliance or arcs in humid conditions.

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4) Mechanical locking (this prevents most real failures)

If your product experiences:
• vibration
• movement
• shipping shock
• users pulling on cables

Then you need:
• latch/lock connectors
• friction lock
• screw lock (for external ports)
• strain relief

Common locking styles:
• Friction lock: simple retention
• Positive latch: click-lock, better vibration resistance
• Screw lock: best for field cables and harsh environments

Common mistake:
Using a non-locking connector in a vibrating product → intermittent resets that are hard to reproduce.

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5) Mating cycles (how many plug/unplug times)

Some connectors are designed for:
• 10–30 cycles (internal assembly)
• 500–10,000 cycles (USB and other user ports)

If users plug/unplug often:
• choose connectors rated for high mating cycles
• choose robust contact plating

Common mistake:
Using a low-cycle connector where users plug daily → wear, loose contact, failure.

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6) Contact plating (hidden reliability factor)

Common plating:
• Tin: cheaper, fine for internal and low cycles
• Gold: better for low-level signals and repeated mating, corrosion resistance

If your connector carries:
• very small signals (sensor, audio, data)
• repeated mating
• humid/corrosive environments

Gold plating is often worth the cost.

Common mistake:
Tin plating in humid environments → oxidation → intermittent signal failures.

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7) Environment: heat, humidity, dust, chemicals, and vibration

If the product is used outdoors or industrial:
• consider sealed connectors or higher IP rating systems
• check temperature rating of plastic
• avoid designs where water can sit inside the connector

For harsh environments, look for:
• sealing (gaskets)
• strain relief
• robust mechanical shell
• corrosion-resistant materials

Common mistake:
Choosing a standard connector for outdoor use → corrosion and failures after months.

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8) Assembly and manufacturability

Connector choices affect:
• assembly time
• rework difficulty
• yield

Decisions to consider:
• through-hole connectors are mechanically stronger but may cost more to assemble
• SMD connectors save assembly steps but can be weaker mechanically unless reinforced
• if cable is crimped: make sure your factory can crimp reliably (tools + QC)

Common mistake:
Choosing a connector that requires specialized crimp tooling you don’t have, causing inconsistent field failures.

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Connector types: quick guidance by scenario

A) Board-to-wire (internal power/signal)

Good when:
• you need removable cables inside the product
• want quick assembly

Look for:
• locking latch
• appropriate wire gauge support
• crimp quality

B) Board-to-board (stacking modules)

Good when:
• you have a main board + daughter board
• want compact connection

Look for:
• alignment tolerance
• mechanical stability
• insertion/removal needs

C) External user connectors (USB, DC jack, etc.)

Look for:
• high mating cycles
• strong mechanical anchoring to PCB
• ESD protection strategy
• strain relief in enclosure

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Common connector mistakes (real-world)
• Choosing by footprint only
• No locking in vibration environment
• Running too close to current rating → heating and failures
• Wrong wire gauge or poor crimp quality
• No strain relief → cable pulls break solder joints
• No ESD strategy for external ports → damage in the field

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Practical connector selection checklist

Before finalizing a connector, confirm:
• Pitch fits current needs and space
• Current rating has margin at your temperature
• Wire gauge and crimp contact support your current
• Locking/retention matches your vibration and user handling
• Mating cycles match expected plug/unplug frequency
• Plating matches environment and signal sensitivity
• Package and mounting style match mechanical strength needs
• Assembly tools and QC process are available