This engineering brief presents common errors associated with wire ferrule installation. It begins with wire stripping and concludes with the quality assessment shown in Figure 1.
Let’s be blunt. Incorrectly crimped wire ferrules are a liability.
Set high standards and immediately reject questionable installations. It’s a painful experience, but not nearly as painful as plant downtime and the cost of troubleshooting latent failures over the lifetime of the equipment.
Figure 1: Standard for wire-ferrule crimps.
This article is part of the DigiKey Field Guide for Industrial Automation
Location: Integrate It → Panel Construction.
Learning Pathway: Industrial Automation Technician → Fundamentals
Difficulty: 
Student — difficulty levels explained
Author: Aaron Dahlen | MSEE | Senior Applications Engineer, DigiKey
Last update: 04 Aug 2026
Strip
The crimp is wholly dependent on properly stripped wire. This demands proper setup of the wire-stripping tool. Figure 2 shows the results of a properly adjusted wire-stripping tool. Observe that insulation is still attached to the wire.
In my experience, this condition indicates that the tool is set for the minimum amount of bite force required to strip the wire. By contrast, consider Figure 3. In this image, a similar stripper was used but the insulation-cutting depth was increased. The insulation ends are wholly removed by the tool. At least one failure is observed as several broken wire strands are visible in the circled area.
Strip length is covered in the inspection section.
Tech Tip: Leaving the stripped wire partially attached (Figure 2) has an advantage during assembly. It protects the conductor’s strand lay and shape during handling. Removing the insulation piece at the last moment, just before adding the ferrule, can save time as there is no need to manually twist the wire or otherwise fight with wire insertion.
Figure 2: Properly stripped wire.
Figure 3: Wire strip failure as broken strands appear in the removed insulation.
Crimp
Figure 4 shows the proper placement of the wire ferrule into the crimping die of a crimp tool.
- Only the ferrule’s metal body is held by the tool’s jaws.
- The plastic insulating collar is touching the jaws but does not enter the jaws.
- An axial force is applied to the wire in the direction of the red arrow.
Figure 4: Placement of the wire and crimp into the tool’s crimping die.
Crimp Inspection
The proof is in Figure 1. From left to right:
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Pass: The termination on the left is the standard. We see that the ferrule’s metal barrel is fully crimped. There are no marks on the plastic. Finally, the end of the wire extends slightly from the tip of the ferrule.
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Fail: The ferrule barrel is not fully crimped. There are only two compression surfaces as compared to the four on the metal barrel of the standard. This increases the wire-to-ferrule resistance. This may cause problems many years down the road as resistance may causes localized heating which further accelerating the oxidation and potentially harms the insulation. It looks bad when terminal blocks and insulation show signs of overheating.
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Fail: This is the worst failure in the bunch as there is no wire crimp whatsoever to the metal barrel. Instead, the crimping force has been applied to the plastic insulating collar. The danger is that it may be good enough to pass the initial tug test. Reject it immediately or you will be dealing with intermittent electrical faults. As a rule of thumb, it’s easy to fix things early but very expensive once the panel is assembled and operational.
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Fail: The final crimp example initially looks correct. However, careful inspection reveals that there is no wire protruding from the end. This could be caused by insufficient wire strip length or a wire that was not fully pushed into the barrel. Either way, it’s difficult to inspect the crimp quality if the wire end is hidden inside the ferrule.
Next Steps
This article provides a student-focused overview of wire crimp quality. It’s a good place to start, but it is only the beginning.
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Consult the regulations applicable to your panel shop. The code(s) may require every crimp to be completed using only the manufacturer-recommended ferrules, conductors, and crimping tools.
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Look outward from the ferrule to what it is connected to. This extends the selection process to the physical shape of the crimp as described in this article. These are system-level requirements that encompass everything the crimp touches.
Parting Thoughts
Establish the standard and reject all workmanship that does not meet that standard.
About This Author
Aaron Dahlen, LCDR USCG (Ret.), is a Senior Applications Engineer at DigiKey in Thief River Falls. His background in electronics and industrial automation was shaped by a 27-year military career as both technician and engineer, followed by over a decade of teaching.
Dahlen holds an MSEE from Minnesota State University, Mankato. He has taught in an ABET-accredited electrical engineering program, served as coordinator of an electronic engineering technology program, and instructed military technicians in component-level repair.
Today, he has returned to his home in northern Minnesota, completing a decades-long journey that began with a search for capacitors. Read his story here.