Crimping 101: Making the Connection

Crimping compresses a terminal’s metal barrel around a wire conductor to create a solderless electrical connection. Done correctly, it provides a secure mechanical bond and low electrical resistance. 

A properly formed crimp helps protect the contact interface from wear and corrosion; using sealed terminals or applying adhesive-lined heat shrink tubing can help make the connection waterproof as well.  

Crimping may seem simple: strip the wire, slide on a terminal, and squeeze. But one poor crimp can cause intermittent faults, overheating, or equipment failures that lead to time-consuming troubleshooting and costly repairs.

Reliable crimps start with three steps: prep, crimp, and inspect.

How to Crimp Terminals in 3 Steps

Step 1: Prep

Select a terminal rated for the application and compatible with the wire’s conductor size, material, stranding, and insulation diameter (for related information see Waytek’s wire ratings and sizing charts).

Use a proper wire stripper, such as the Pressmaster stripper/cutter shown below. Check the terminal manufacturer’s recommended strip length, set the tool accordingly, and remove the insulation without cutting or nicking the strands.

Inspect the stripped end for damaged or missing strands and leftover insulation. If damaged, cut off that section and strip again. Keep all strands together; do not trim strands to fit an undersized terminal.

Step 2: Crimp

Crimping eliminates the soldering step and can speed installation. For vehicles and mobile equipment, a properly made crimp with suitable strain relief (such as heat shrink) will also help the connection withstand vibration.

Use the terminal manufacturer’s specified or recommended crimping tool and die. Select the correct cavity for the terminal and wire size. General-purpose pliers or an incompatible die can produce a connection that looks secure but fails to meet specifications.

Many professionals use ratcheting crimp tools because the ratchet normally prevents the jaws from opening until the crimping stroke is complete. Some tools have color-coded cavities to help match compatible terminals and wire sizes. Neither feature verifies crimp quality: correct tooling, setup, and inspection are still essential.

Position the terminal in the die as directed by the tool manufacturer. Insert the stripped wire fully so all strands enter the conductor barrel and the insulation stays outside the conductor crimp. Where provided, the insulation support should grip the insulation, not the bare strands.

Keep the wire in position and complete the full crimping cycle. For terminals requiring multiple crimps, follow the specified number, locations, and sequence. Remove the terminal carefully and inspect it before use.

Step 3: Inspect

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A reliable connection needs more than a quick glance. Inspect each crimp visually, using magnification when needed, and follow the manufacturer’s acceptance criteria for the terminal design. Make sure that:

• The crimp is in the specified location, with no cracks or distortion that could affect function.
• All conductor strands are captured in the barrel, with no loose strands or insulation trapped in the conductor crimp.
• The conductor end is positioned as specified. Where a slight strand protrusion is required, it must not interfere with the terminal’s mating or mounting area.
• The insulation support, where present, holds the insulation without cutting through it.

Right: For more examples of acceptable and unacceptable open- and closed-barrel crimps, see Molex’s comprehensive Visual Crimp Inspection Chart.

Where specified, use a crimp micrometer to measure conductor crimp height at the prescribed location and compare it with the manufacturer’s limits. Check crimp width and insulation crimp dimensions where applicable specifications call for them.

For sample crimps, use a pull tester to verify that the connection meets the manufacturer’s minimum pull-force requirement. Follow the specified test method, including how to handle the insulation support. Pull testing is destructive; do not install samples that you have pull tested.

If a crimp fails inspection, cut it off and start again with a new terminal. Consistent preparation, correct tooling, and inspection help prevent weak connections and costly failures.

For related topics see How to Choose the Right Crimping Tools and Wire Crimping Tools & Techniques by Molex.

See a wide selection of crimp tools from Molex and other leading manufacturers at WaytekWire.com.