Introduction

Over the years I’ve tried many sorts of wire strippers, ranging from knives!, cheap adjustable wire strippers, combined crimp/strip tools and so on. I was not happy with most of them. They were either just good for a very limited range of wires, or the results were unreliable and required a lot of effort to provide a good strip without damaging wires, or the tool itself didn’t last as long as desired.

Life is too short, and so a while back I figured it was about time to invest in decent wire strippers. I currently have three now which I use regularly. All the others lie unused. This blog post is specifically about one of the three wire strippers which I’m using, the Knipex 12 12 06Knipex 12 12 06, because it strips a very handy range of wires, with great results.

It is very unusual in that it has four blades, instead of the usual single blade, or two blade strippers. It’s got a lot more bite!

Check out the twelve minute video for all the detail:

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Knipex Precision Wire Insulation Strippers Review - Model 12 12 06

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Wire Stripper Requirements

There are tons of low-cost wire strippers, and some (not all!) perform their task adequately provided the application is non-critical and nothing demanding is asked from them.

As needs increase, they are no longer adequate. I can’t trust them to ensure zero strand loss when stripping wires. Some are especially useless with high-performance insulation such as PTFE, which is harder than PVC. The repeatability is a major issue with low-cost wire strippers. When I’m having to strip a dozen wires for a connector, it is really tiresome if some wires get accidently cut or nicked, and then all the wires are no longer the same length unless I trim all other wires.

From my perspective, I’m looking for quite a few things in the resultant stripped wire end.

Stripped to the correct length

Some wire strippers do not help in this respect, and the wire needs to be measured with a ruler.

No nicks or cut strands

This ruins the wire! It is easy to damage wires with the types of wire strippers that have a screw adjustment, because the screw position can be set incorrectly.

Sharp cut to the insulation

Remnants of insulation that extend into the stripped area are not great. The insulation should be cut as neatly and as squarely as possible. Many wire strippers which require manual adjustment cause this issue; the insulation is not stripped adequately, and then the insulation needs trimming with wire-cutters.

Short wire capability

Some wire cutters cannot handle short wires, often removing the insulation off the entire short length of wire!

Short strip capability

Some wire cutters cannot strip just a couple of millimetres of insulation; instead, the insulation just stretches!

Long strip capability

The ability to strip a long length of insulation in one go is handy when the wire end is to be wrapped around a post or fit in a deep screw terminal such as with some banana plugs.

Ability to handle multiple insulation types

Some wires have soft insulation, others have hard insulation. Some wires have fat insulation, others are thin-walled. Ideally the wire stripper should cover as many thicknesses and hardnesses of insulation as possible!

Ability to handle different wire thicknesses

Manually adjusted wire strippers can take a lot of tweaking! Automatically adjusting tools can help here.

Low operating force and ease of use

Some multi-crimp/strip tools are awkward to hold, and require a lot of force to hold the wire, especially if the wire is short and cannot be gripped easily

Consistency, reliability and value for money

The tool must be usable repeatedly with low wire strip failure rate, low wire nick/strand cut rate, and must last a long time, particularly if the tool has a higher cost

Wire Stripper Testing Strategy!

I’ve gradually accumulated an assortment of wires of popular types and thicknesses over the years, and so I thought I’d use these to test the tool. In particular, I primarily tested equipment wire used for constructing projects and internal chassis use, but also some consumer inter-equipment wire like speaker wires. Although the tool is not designed for coax cable, I tried that too! I deliberately did not test non-stranded wire for a couple of reasons; I use a different, lower-cost pair of wire strippers for that, and secondly, internal equipment wire is nearly always stranded except at very small diameters.

In order to test the wire stripper, I used less than two inch (50mm) lengths of wire; this is a very short length, but I wanted to test the wire stripper to see what would happen with such short lengths of wire!

I stripped each wire twice; the first strip was to remove about 3mm off the end. The second strip was to the same wire end, and was an additional 15mm (to total 18mm overall). This way, I could examine for wire nicks easily after the second cut, and also establish if the insulation could be removed in such a small amount of length (3mm) and if it was possible to strip long lengths of insulation too.

With 24 different wires to test, I kept notes about each wire, and also collected up the wires and stripped insulation photographs so I could explore further.

The wires were split up into seven categories:

Using the Knipex Precision Insulation Stripper

See the video earlier for more detail, but in a nutshell all that needs to be done is a single adjustment – the wire strip length! After that, the wire is inserted into the appropriate hole  - usually this is very easy to do, there are only six holes to choose from, and mostly it is very clear which one will cut the insulation without touching the wire - but there are engravings on the blade with the wire cross section values marked too.

Next, the handle is squeezed and everything is over within a second! In slow motion, you’ll see that the blades dig into the insulation first:

Then, as the handles are continued to be squeezed, the blades automatically pull apart the insulation, and then the jaws open, releasing the wire.

Anyone can use this tool. There is no trimming/adjustment for different wires, and the force required on the handles is way less than the force for wire strippers where the operator needs to pull on the wire! This tool is used single-handed.

Onto the test results! The tests below record which hole was used to strip which wire. This is the numbering I used:

1: PVC Insulated Equipment Wire (Rated Wire)

Four different wires were tested.

At a 3mm stripping length, there was no issue stripping these wires at all. Everything looked good! If you examine the photo closely, it I possible to see that the blades sliced and tore off the insulation fairly cleanly! There are places where there seems a step in the insulation where a blade on one side of the too or the other side tore off the wire first, but this step is small, about just under half a millimetre. This distance corresponds to the distance between the blade pairs on the tool as far as I can tell.

Stripping an additional 15mm (to total 18mm overall) also provided really great results. Note that for all these photos, I did not try to twist the wire strands; the photos are of the wires as they were left by the stripper.

I loves that it was possible to accurately cut wires, since the blades do not slip. Once they bite into the wire, that is precisely where the wire will get stripped. This is very useful for multi-wire connectors where all the cores of a cable must be stripped with accuracy.

2: PTFE and MPPE Equipment Wire

A far more challenging test than PVC wire could be that with harder insulation! So I wanted to try PTFE wire with the wire strippers. Also, some PTFE wire has very thin walled insulation in comparison with PVC insulation. This too may have an effect, and so I grabbed all the different wire types I had. There were two PTFE insulated wires, and one that had Modified Polyphenylene Ether (MPPE) insulation. MPPE is stronger and lighter than PVC, so a thinner wall is adequate, and some typical wires can be around 65% lighter as a result. It is recyclable and has flame resistance rating, and is far lighter than PTFE too.

PTFE insulated wire has excellent stability in humid and liquid exposed conditions, and is resistant to bending and stresses over time, and is suitable for high temperature environments.

At 3mm stripping length, everything was fine.

When stripping off the additional 15mm (18mm total), for the blue insulated wire, the stripping action caused the wire to come out from the remainder 32mm. With a longer 100mm length of wire, there was no issue. This was a challenging test, having a very short 50mm wire length with PTFE insulation. I think it is very minor, and for scenarios where such a short wire is needed, it is sometimes possible to grip the wire by hand, to apply a bit of compression on it.

I did not count this as a failure; I feel PTFE+50mm wire length in such a gauge of wire is very extreme! Furthermore, the conductor was not damaged in this test (or any other test, apart from when the incorrect hole is used, as shown later).

3: PVC Wire, unrated (hobby wire)

This was basic, low-cost wire consists of PVC insulation and often tinned copper wire. I tested four different wires. The wires in rows 3 and 4 are the ones you'd use with a breadboard:

Again at 3mm there was no issue:

Stripping an additional 15mm cause no issue. All was good!

4: Extra Flexible (High Strand Count) Test Lead Wire

Test lead wire can be a challenge for some wire strippers, because the strands are very thin so there could be a risk of nicking them while stripping. The insulation is sometimes softer than normal too (for example silicone can be used).

Four wires were tested:

I was very impressed to see that the wires were stripped perfectly at 3mm length, with no accidentally cut strands. The twin wire was a bit unusual; it had a thin outer black insulation, but then it had a red or blue insulation underneath that. I originally tied tool hole #3, but it succeeded in only stripping the outer black insulation layer. Hole #4 worked very well for it however, allowing the outer and inner insulation to be stripped.

The story was different when an additional 15mm was stripped. Here, using tool hole #4 did not work well for that particular wire as can be seen in the photo below, but hole #3 gave a perfect result. The conclusion was, for some test lead wires, using the correct hole doesn’t work for extremely short 3mm wire strips. This makes sense, because the insulation is soft and presumably it is difficult for the tool to get a good grip of both of the insulation layers at such a short distance from the wire end. The solution is to strip a longer length such as 10 or 15mm for such unusual double-insulation silicone wires.

At 15mm the results were tremendous. I was really impressed. The lay of the wire was good, it was not disturbed, and the insulation was stripped cleanly. It is really annoying when the lay of the wire is disturbed, especially if it needs to be then inserted into a close-fitting connector or ferrule.

5: Speaker Wire

I tested four fairly bottom-range speaker wires. Low-end speaker wire sometimes has very small diameter conductor, but very thick insulation to make it look like it is worth more – a bit like some cheap car battery jump-start cables.

I tested four wires:

There was no issue stripping the wires by 3mm:

And there was no issue stripping the wires by an additional 15mm either!

6: Coaxial Cable

I was curious if the wire strippers could be used to strip the outer insulation on coax cables. For this test, I tried just two different cable types, but I might revisit this and test more types in future.

The first wire has a very thin outer insulation, and it was too easy for everything to come of the remaining insulation when trying to strip it. With a longer 100mm length it was possible to strip off 3mm.

The second wire was a very tough test I thought. It has a very tough but thin outer insulation, and the braid has many strands and is very thin. I didn’t expect the were strippers to succeed here, but they surprised me. The wire was stripped by 3mm successfully.

Stripping an additional 15mm proved difficult for both wires, unless the wire length was 100mm or so. At 50mm, the remaining insulation would slide out. However, I was highly impressed that the results did not damage the wire, and the lay of the braid was left intact too.

7: Mains Cable

I’m unlikely to use these strippers for mains cable often, but I thought I’d try it anyway. These are the usual UK two or three core mains flex cables, which I don’t use that much, given that most things use mains connectors and pre-assembled cables these days.

There was absolutely no issue stripping these wires.

The additional 15mm stripping had no issue either:

Summary

The Knipex tool has performed exceptionally well. It is easy to use (just six holes to choose from, and it becomes very easy to eyeball which hole to use for which wire), doesn’t require much skill to use (no adjustments apart from stripping length) and in normal use, in my tests over the 24 different wire types I did not lose a single wire strand (strands were lost when I used the incorrect hole for the unusual double-insulated test lead wire), and it worked pretty well with short wires (50mm long) that were stripped by a large amount (more than 15mm) which is effectively 30% of the entire insulation! Some of the wires did require a longer length of 100mm however, to prevent the rest of the wire from coming out of the insulation.

The range of wires that the tool can handle is very good too; it is impossible to find a single tool that will meet all wire stripping needs, but this covers a large proportion, so that too makes the tool worthwhile.

I love that this tool lives up to its name and is very precise. Once its teeth grip the wire, then that wire is accurately stripped, and to date I’ve not seen the tool fail during a single strip, apart from operator error (selecting the wrong hole, or missing the hole).

When I’m working with microelectronics I do need to be able to also strip 30AWG wire (this is a popular gauge for Kynar and Tefzel single cored wire) so that would need a different tool since the Knipex tool does not go down to 30AWG. For that I use a different tool, so I’ll review that later.

In summary I think the tool performs extremely well. It appears very well constructed, it has lasted me a year so far (and spare blades are available although I have not needed them so far), and I think it will continue to provide many years of good service. The very unusual design provides a very reassuringly precise result, and I can see that a lot of engineering must have gone into designing a tool that can repeatably position so many blades accurately. This is my favourite pair of wire strippers by far!