Table of contents

RoadTest: Knipex Self Adjusting Crimping Plier

Author: shabaz

Creation date: 1 Sep 2016

Evaluation Type: Independent Products

Did you receive all parts the manufacturer stated would be included in the package?: True

What other parts do you consider comparable to this product?: Considered other Knipex brand products too, which perform the crimp operation to a different cross-section. A square cross-section met my needs more. Some generic (lower cost) crimp tools were also considered but were ultimately eliminated due to no stated compliance to DIN standards

What were the biggest problems encountered?: No problems encountered with the tool

Detailed Review:

Introduction

I’ve often found it difficult to achieve a satisfactory result by directly soldering or screwing stranded wires into a connector. Wire strands can break through wire flex, or might be overly crushed by the screw or pushed out of the way of the screw, leaving few strands in good contact.

Many modern screw terminals protect the wire from being crushed directly by the screw but not all screw terminals have this feature.

When wires are temporarily unscrewed, if they were excessively crushed against the screw then strands will have broken and the wire end will need to be cut and be re-stripped before screwing it back into the connector.

Furthermore wire strands are susceptible to breaking with vibration or repeated flexing at the interface with the terminal/screw/clamp unless some strain relief is possible. It is a regular occurrence for soldered wires to break off circuit boards due to turning the circuit board over a few times during design or test.

One possible solution to these problems was to use ferrules; I finally bit the bullet and purchased a tool to try it out. To see it in action, click here: Make your own Test Leads; Assembling 4mm Banana Plugs

Which tool?

I settled on trying the Knipex range for three reasons. Firstly it was a trusted brand from a company in existence for over 130 years, and I hope the product will live up to the brand’s reputation. I have 20-year old Knipex pliers and they still function well.

Secondly it was actually very affordable for a tool that, if it worked like my pliers, could provide many years of reliable service – I don’t want an unreliable tool.

Thirdly the Knipex tools were designed and tested specifically to the DIN 46228 parts 1+4 standards. These are German standards but are useful worldwide because they dictate precisely what size and thickness the ferrules are, so you know that if you purchase the correct ferrules from any manufacturer that claims compliance with that standard then the tool will function correctly with them. It also defines the tests that the tool must pass; the crimped result must be able to withstand certain tensile strain so that the wire does not come out of the crimped ferrule. I would not want a tool that did not have such compliance. If you’re going to the lengths to crimp a wire then you’ll probably want reassurance that the wire won’t come out, and the ferrule won’t accidentally crack or fail; the standard precisely specifies the ferrule material too. It must be tinned copper.

After spending a long time checking out the extensive catalog I settled on the Knipex 97 53 04Knipex 97 53 04 (it also comes in a kit with box, ferrules and a wire stripperkit with box, ferrules and a wire stripper) which transforms the ferrules into a square cross-section. A square cross-section provides a lot of contact for the flat bottomed screws in terminals. There are other tools that create different cross-sections such as hexagonal which geometry dictates will allow the crimped ferrule to fit inside a smaller hole (a 14% larger diameter circular hole is needed for a square shaped peg compared to a hexagonal one with the same cross-sectional area).

Ergonomics

The tool is reasonably comfortable. There is a two-part moulding where the dark blue is a slightly softer material and the red part is hard plastic. It is shaped to be held in one direction, there is some ergonomic difference if it is held incorrectly. However the tool provides ingress to the ferrules from both sides and therefore it can be held with identical optimum ergonomics in either hand as a result.

The handle/lever which is connected to a ferrule size adjustment ring is the handle which is at the finger end when holding it correctly. The other handle rests in the palm.

Regarding the plastic handles, personally I’d prefer an even softer plastic at the location where it presses against the palm but I’d have to be fitting hundreds of ferrules in a short space of time to feel any impact.

Using it

It is really easy to use. Strip the cable using your normal tools, twist the strands so they lie in their original place and slip on the recommended sized ferrule over it. Then insert into the tool and fully press and release. Not as much force is needed as I thought would be required.

The Knipex website has a product video, but using the tool was straightforward and therefore although the video is not mandatory viewing to learn how to use the tool, it is worth watching anyway.

The tool provides reassuring ratcheting noises as it is used. It won’t open until it has fully crimped the ferrule but the tool can be opened using a tiny abort lever if things were to go wrong. There were no squeaks or rubbing noises; it works well and there is very little visible oil. The tool is dry and I see a very tiny amount of oil (around 0.5cm² of area) when the levers are fully opened, close to the moving parts of course; I would store it in the semi-ratcheted state to reduce the space the levers will occupy anyway, and the oil will not touch or get rubbed off. The tool is exceptionally clean and non-greasy. My hands are in great state after using this tool.

There is a ferrule size adjustment ring which has two settings (it is pulled out and then turned and then pushed into place); the default setting is for all ferrules up-to and including 10mm² area. The other setting is for the largest 16mm² area ferrule. I will not encounter 16mm² often so for me it will almost never be moved from the default setting. A good tool will have such a selection ring for the larger size because the tensioning needs to change; the largest ferrules are of slightly thicker material.

I really like that the tool has no visible tensioning adjustment ‘tweaks’ like some tools have. It is pre-set at the factory and no such adjustments are ever needed by the user. I also liked that it can be used with a very large ferrule range, for wires from 28 AWG to 5 AWG.

Which ferrules?

It is good to buy lots of different sizes! It is possible to get away with just a few sizes but you do want to try to match the wire diameter to the ferrule diameter if possible. Worst case one could fold up the wire and insert it double-thickness into a larger ferrule if the correct sized one was not to hand. The colours of the ferrules are just a convenience, as an indicator of the size. However there are several color standards! Including a French standard and a German one so it could be preferable to pick a side and stick with it.

There is a nice Multicomp set of popular size ferrules in a handy rotary container but it is small, so is really only ideal for putting into a tool box when you’re mobile. At home or in the office it may be best to get a larger container to house more ferrules, and a wider range if you’ll encounter different wire thicknesses in your line of work. In the UK the ‘Wham’ boxes are quite good and they are available from stores locally (WHSmith and Staples).

A question I had was; how does one decide which ferrule suits which wire? Some spools of cable are labelled with the wire gauge (American or Standard) and others are labelled with the wire diameter or number of strands and each strand diameter, and some are labelled by cross-sectional conductor area. Also, how to decide which diameter hole will allow the crimped ferrule to fit? I could not find any guidelines/summary so the one in the image below was created and I’ll refine it over time if people find errors or have suggestions. It does not cover all ferrule sizes, only the popular sizes that I had at hand. If you’re purchasing popular sizes then you could print the diagram and stick it on the box. It lists the closest wire gauges that suit the ferrule as well as the ferrule inner diameter and recommended copper cross-sectional area and a suggested hole size that would allow the final crimped ferrule to be inserted inside a terminal; for this I have allowed about 0.5mm tolerance because in certain cases the crimped result may be slightly rhombus (diamond) shaped instead of square if the wire was too thin for the ferrule. (Note: the information is provided with no liability; it is up to you to verify the detail before use). The tolerance value was selected through some experimentation with the ferrules and measuring the result with a micrometer. If the wire diameter is excessively thin for the ferrule then the ferrule does not take a square cross-section because it is impossible to maintain a crimped result without distorting the shape and it can naturally take a crushed or diamond shape in this case. It is not a fault of the tool, it is doing its best in this case to crimp to a wire that is of the incorrect diameter.

If an unknown diameter wire is to be used then it makes sense to test the crimped result on a test wire by at least pulling at it forcefully. With the wires I tested, it was not possible to separate the ferrule from the wire by hand no matter how hard I tried.

Example applications

I tried the ferrules with mains plug wiring. It is possible to get bare ferrules without the plastic sleeve and this suits the cramped space within a plug. For such 13A rated mains cable 0.75mm² ferrules are used.

It was really easy to get the mains plug wired. Ordinarily I might try to fold the wire to try to get as much of it screwed down as possible. With the ferrules it was possible to get the screws nicely centred for maximum contact and no damage to the wire either. Here is what it looks like after the plug is subsequently unscrewed:

The wire is completely intact and could be re-attached to the plug.

Another use-case I wanted to try was very thin wires. I tend to use 10/0.1mm wires (ten strands 0.1mm  diameter each) often for electronics circuits but they break after a while if directly soldered to a PCB with no strain relief, or screwed into a PCB terminal. The overall strand bundle thickness is 0.3mm which is about 28 AWG. The smallest ferrule I had was for 26 AWG. The solution was to fold the wire to double it up before inserting it into the ferrule. The result was stronger than the wire (when pulled, the wire snapped but the wire did not slide out of the ferrule).

Although the result worked, it may be better to find thinner ferrules for such thin wires, to save the effort of folding the wire strands.

Another use-case is direct to PCB wiring; I needed to test this for a TO-220 device that was initially designed to fit a PCB but was later decided to be attached to the chassis for better heat-sinking.

The 24 AWG rated ferrules (turquoise) were perfect for using with the wire from a LAN cable (Cat. 5 cables are a cheap source of wire!).

Note that for such PCB use the ferrule should not be trimmed by more than a couple of millimetres. Also, it is strongly advised to trim before soldering (prevent shock to the PCB).

The result was great. The plastic sleeves prevent excessive flexing close to the join and therefore the PCB can be moved many times with far reduced risk of the wires breaking. For further strain relief a heat shrink sleeve could be placed over the plastic insulator portion of the ferrule but it is probably unnecessary for most use-cases.

The smallest ferrules I had (the light blue and turquoise ones, i.e. 24 and 24 AWG respectively) once crimped will comfortably fit a 1.6mm diameter PCB hole (this can be seen from the reference diagram earlier) although this is with a tolerance; a 1.3mm hole could be sufficient in many cases.

Ferrules are also ideal for industrial wiring or point-to-point wiring inside a chassis using screw terminal blocks. The risk of wire strands breaking or shorting against adjacent terminals is greatly reduced.

Manufacturers like Phoenix Contact have terminal block ranges which can be speedily wired up if cables are single-cored or if ferrules are used (photos from Phoenix Contact website):

The wires are removed by inserting a plastic tool in an adjacent hole per terminal contact.

The 0.75mm² ferrule perfectly fits the popular Wago terminal blocksWago terminal blocks. This is really good news.

Another great use is for speaker cable, or for car audio, where wires may need to be screwed or clamped down. Ferrules are offered in longer lengths too.

Twin entry ferrules are also available. These are excellent for creating a loom/cable assembly and where junctions of wires are needed that are not intended to be disassembled. One example of this would be the wiring between a fuse and transformer, where a mains neon lamp needs to be wired in parallel inside the chassis.

Summary

Many tasks that require stranded wire termination can benefit from ferrules. The Knipex tool has worked well, with no complaints at all.  It is easy to use, no trimming/adjustments needed and the resultant crimps are impossible (for me) to pull out from the wire and the construction to the DIN standard provides confidence that when used with correct ferrules that a reliable permanent crimp is made. The square cross-section crimping action does provide some flexibility if the incorrect wire diameter is used by mistake, because the tool will continue to crimp the wire and the crimp will gracefully deform into a diamond or other crushed shape.

The tool is competent for large wires (16mm²) as well as the thin 10/0.1mm wires I tried. The small ferrules are great for direct point-to-point wire connections on PCBs.

The tool has solved a lot of problems; I’m very happy that my wire terminations are now unlikely to fray or break off and that I can get neater wiring results with a lot more ease than before.

I would have liked to see a sheet of information or ferrule guidelines with the tool (it comes in a box with no paperwork) but the website makes up for this with a nice product-specific video. The tool functions reliably as expected, a slightly more cushioned handle would have been a nice-to-have but its subjective and perhaps that would have worn out quicker. The build quality looks good enough for me to believe it will certainly provide many years of good service, making the tool extremely cost effective. Now that I am familiar with the tool, my first real application will be to complete an AC power supply that requires internal mains wiring.

Ferrule Guide