Crimping wires with a wire crimper is a key skill for anyone involved in auto electrical, wiring repair, or electronic circuit assembly. Improper crimping can result in poor contact, overheated connections, and even short circuits. This article will help you figure out how to choose the right tool, prepare the wires, and perform the crimp so that the connection will last for years without problems.
We will consider not only the basic technique of working with a crimper, but also nuances that are often silent about in standard instructions. For example, why some terminals require double crimping, how to avoid deformation of the core and what to do if you don’t have a tool of the required size at hand. You will also learn what mistakes beginners most often make and how to prevent them.
What is a crimper and why is it needed?
Crimper (from English. crimp - “crimp”) is a manual or hydraulic tool designed to creating permanent connections between wires and connectors. Unlike soldering, crimping does not require heat, making it a faster and safer method, especially in confined spaces (such as under the hood of a car).
The main areas of application of the crimper:
- 🔧 Auto electrics: wiring repairs, installation of additional equipment (radio tape recorders, cameras, alarms).
- 💡 Household appliances: replacement of power cords, repair of plugs and sockets.
- 🖥️ Network equipment: crimping twisted pair (RJ-45), connectors for telephone lines.
- 🚗 Tuning and retrofitting: connecting LED strips, relays, fuses.
Modern crimpers are equipped replaceable matrices for different types of terminals (insulated, non-insulated, coaxial) and often have crimp force adjustment, which allows you to work with wires of different sections. For example, for automotive wiring, terminals with a section of 0.5–6 mm², and for power circuits - up to 10–16 mm².
Types of crimpers: which tool to choose
There are several types of crimpers on the market, differing in design, purpose and price. The choice depends on the tasks you plan to work with. Here are the main varieties:
| Crimper type | Purpose | Benefits | Disadvantages |
|---|---|---|---|
| Universal | Crimping of insulated and non-insulated terminals | Suitable for most tasks, replaceable dies | Less accurate compared to specialized models |
| For twisted pair (RJ-45/RJ-11) | Network cable crimping | Precise crimp geometry, often with stripping knife | Not suitable for automotive terminals |
| Hydraulic | Crimping of power cables (cross-section > 10 mm²) | High compression force, uniform crimping | Expensive, bulky, requires setup |
| Automatic (with ratchet) | Semi-automatic terminal crimping | Provides uniform force, convenient for serial work | High price, limited selection of matrices |
For auto electricians, the optimal choice will be universal crimper with a set of dies for terminal types OT (open end) ZT (closed end) and DIN. Popular models among professionals - Knipex 97 53 03, Weidmüller 9753100000 and budget options from Jonard or IEK.
Selection advice: if you work with wires with a cross-section up to 2.5 mm², pay attention to the crimpers with color-coded sockets - this simplifies the selection of the correct matrix. For power circuits (such as starter wires), you will need hydraulic tool or crimper with leverage booster.
Preparing wires for crimping: step-by-step process
The quality of crimping depends 50% on proper wire preparation. Even the most expensive crimper will not save you if the wires are damaged or the insulation is removed carelessly. Follow this algorithm:
Strip the insulation to the length of the terminal sleeve (usually 5-7 mm)|Check the integrity of the wires - there should be no breaks or darkening|Twist the wires tightly, but without twisting|Cut off any protruding hairs of the copper wire|Place the terminal onto the wire before crimping (if it is not pre-fitted)-->
1. Stripping the insulation. Use stripper (insulation stripper) or a sharp knife, but do not damage the wires. For thin wires (0.5–1.5 mm²) the optimal length of the bare part is 5–6 mm, for fat people (4–6 mm²) — 7–10 mm. If too much is exposed, the unprotected area may short out to the body.
2. Stranding. The copper strands should be tightly twisted, but not twisted - this weakens the wire. For multi-core wires (for example, PVS) use straight twist, for monocore (for example, PV-1) - just straighten the end.
3. Terminal check. Make sure the terminal you select matches the wire size. Most terminals are marked with a range of cross-sections, e.g. 0.5–1.5 mm². If the terminal is too large, the crimp will be unreliable; if it is small, it will damage the veins.
⚠️ Attention: Never use terminals that show signs of corrosion or deformation. Oxidized copper increases the resistance of the connection, causing heat and a risk of fire.
Crimping technique: how to work with a crimper
Now let's move on to the crimping process itself. Not only effort is important here, but also terminal position in the matrix. Let's consider the process using the example of insulated terminals like DIN 46228:
Step 1: Terminal Positioning. Insert the terminal into the corresponding socket of the crimper so that isolated part was in the wide part of the matrix, and bare vein - in a narrow one. Most crimpers are color coded:
- 🔴 Red - for terminals
0.5–1.5 mm². - 🔵 Blue - for
1.5–2.5 mm². - 🟡 Yellow - for
4–6 mm².
Step 2: Crimping. Smoothly squeeze the crimper handles until they stop. The ratchet mechanism (if equipped) will ensure a complete compression cycle. Do not release the handles until you hear a click. - this ensures that the crimping is performed with the required force. For terminals with double crimp (for example, DIN 46237) repeat the operation for the isolated part.
Step 3: Quality Check. After crimping, pull the wire along the axis of the terminal. If the connection is secure, the wire will not slip out. Also inspect the terminal for cracks or incomplete crimping. Signs of a bad crimp:
- 🚫 The terminal is deformed asymmetrically.
- 🚫 The veins are visible from the outside after crimping.
- 🚫 The wire insulation is damaged by the matrix.
If you don't have the right size crimper on hand, you can use hammer and flat screwdriver, but this is a temporary solution. Carefully crimp the terminal on both sides, avoiding distortions.
Common mistakes and how to avoid them
Even experienced craftsmen sometimes make mistakes when crimping, which lead to unreliable connections. Here are the most common ones and ways to prevent them:
1. Incorrect terminal selection. Using a terminal that is not sized for the wire is the most common mistake. For example, if the wire 0.75 mm² put the terminal under 2.5 mm², the contact will be weak, and the wires may dangle inside. Solution: Always check the markings on the terminal and use cross-section correspondence tables.
2. Incomplete crimping. If you do not press the crimper handles all the way, the terminal will not deform enough to make reliable contact. This is especially critical for insulated terminals, where the underexposure is visible to the naked eye. Solution: Use a crimper with a ratcheting mechanism that locks the release until the cycle is complete.
3. Damage to cores. When crimping stranded wires, individual hairs can be cut by the sharp edges of the terminal, which reduces the cross-section and increases resistance. Solution: Before crimping, twist the strands and trim any stray hairs.
⚠️ Attention: Crimping aluminum wires requires special terminals and tools! Aluminum flows under pressure, so the connection weakens over time. For auto electricians use only copper wires.
What happens if you crimp the terminal twice?
Repeated crimping of the same terminal may result in microcracks in metal, which will weaken the connection. If the first crimp turns out to be of poor quality, it is better to cut off the terminal and put on a new one. The exception is terminals with double crimp (for example, for coaxial cables), where the second crimp is provided by design.
Crimping without a crimper: temporary solutions
Situations when a crimper is not at hand, but the wire needs to be crimped urgently, happen often. In such cases, you can use improvised means, but remember: this temporary solution, and the connection should be redone as soon as possible.
Method 1: Pliers + Hammer
- 🔨 Place the terminal with the wire attached on an anvil or hard metal surface.
- 🔨 Gently crimp the terminal with a hammer through pliers, evenly distributing the blows.
- 🔨 Check the connection for strength - pull the wire.
Method 2: Vise
- 🔧 Clamp the terminal with the wire in a vice, first placing soft metal (for example, an aluminum plate) to distribute the pressure evenly.
- 🔧 Tighten the vice smoothly, avoiding distortions.
Method 3: Screwdriver and nail (for small terminals)
- 🔩 Insert a nail into the hole of the terminal and crimp it on both sides with a screwdriver, simulating the action of a crimper.
These methods are suitable for emergency repairs, but do not guarantee durability. For example, crimping with a hammer may deform the terminal unevenly, resulting in increase in resistance and heating the connection.
Checking crimp quality: how to ensure reliability
Even if the crimp looks good visually, it does not guarantee reliable contact. Here's how to test the connection before installation:
1. Visual inspection:
- 👁️ The terminal must be deformed evenly, without cracks.
- 👁️ The wire insulation should not be damaged.
- 👁️ The cores should not protrude from the terminal.
2. Mechanical test:
- 💪 Pull the wire along the axis of the terminal with force
5–10 kg. If the wire does not slip out, the crimp is secure. - 🔄 Twist the terminal around the wire - it should not scroll.
3. Electrical test (optional):
- 🔌 Use the multimeter in mode
callsto check the connection resistance. It should be close to zero (<0.1 Ohm). - 🔥 If the terminal heats up when current flows, this is a sign of poor contact.
For critical connections (e.g. starter wires or power wiring) it is recommended to use heat shrink tube over the terminal. It not only insulates the connection, but also prevents moisture from entering, which is especially important in the engine compartment.
A high-quality crimp must withstand mechanical loads and not heat up at the rated current. If the connection gets hot, it needs to be redone, even if visually everything looks fine.
FAQ: Frequently asked questions about wire crimping
Is it possible to crimp aluminum wires with a regular crimper?
No, aluminum requires special terminals and tools. Regular copper terminals are not suitable as aluminum oxidizes and “leaks” under pressure, causing the connection to become loose. For aluminum, use terminals with anti-oxidation paste (for example, Alu-Crimp) and a crimper with adjustable force.
How to crimp a wire without stripping the insulation (for example, for “pierced” terminals)?
For this purpose they are used insulated push-in terminals (for example, Wago 222 or 3M Scotchlok). They do not need a crimper - the terminal is latched manually, and the knives inside cut through the insulation, ensuring contact. However, such connections are less reliable than crimping and are not suitable for high currents.
What is the difference between DIN and JIS terminals?
Terminals DIN (German standard) and JIS (Japanese standard) have different crimp shapes. DIN provides tighter contact due to U-shaped deformation, and JIS - due to B-shaped. Most often used for auto electricians JIS, as they work better with thin-walled terminals.
Is it possible to solder crimped terminals for greater reliability?
Technically it's possible, but it's not recommended. Solder makes the connection brittle, and when heated, the terminal can become deformed. The crimping itself ensures reliable contact if done correctly. Soldering should only be used for stranded wires without terminals (for example, when repairing printed circuit boards).
Which crimper is best for beginners?
Suitable for beginners universal crimper with ratchet mechanism and a set of matrices for terminals 0.5–6 mm². Good budget options: IEK KW PC16 or Jonard CR-100. They are easy to use and cover 90% of auto electrical tasks.