Poor contact at the connection point of a multi-core wire often causes local overheating of the insulation and melting of the battery terminals. If you notice that the wire KG or PV-3 at the place of entry into the clamp sleeve blackened or emits a characteristic smell of burning, this is a direct signal that the used tip is selected incorrectly or mounted with a violation of technology. Ignoring this symptom leads to an increase in transient resistance, which in the conditions of the on-board network of the car with currents up to hundreds of amperes is fraught with fire.
The problem lies in the structure of the conductor itself: individual thin veins without mechanical sealing cannot provide a tight press to the walls of the contact platform of the bolt connection. A standard screw, even tightened with effort, is not able to evenly squeeze a loose bundle of copper, leaving air gaps between the veins. It is to eliminate this physical incompatibility that it is intended to multi-coreIt turns a flexible beam into a monolithic cylinder.
In an automotive electrician where there is constant vibration, temperature changes and exposure to aggressive environments, the quality of the contact connection is a critical safety parameter. Incorrectly selected or installed contact details can cause a failure of the starter, generator or loss of control of the electronics of the engine. In this article we will analyze the technical nuances of choice, marking and installation technology, which will exclude such risks.
Design features and types of tips
The main element of the design is a tailing, or sleeve, where the cleaned part of the cable is inserted. For multi-core wires, the inner surface of the sleeve is often done with notches or roughnesses, which improves copper grip and prevents the wire from turning inside after pressing. The material of manufacture is usually electrical copper grades M1 or M22It provides minimal resistance to current.
Depending on the operating conditions in the car, the tips are divided into several key types in shape and protection:
- 🔌 Copper lawn (TML) - covered with a layer of tin or tin-bismuth alloy to protect against corrosion, which is critical for the under-hood space with high humidity.
- ⚡ Copper squats (TM) - are intended for dry rooms or interior parts of the cabin, where moisture and aggressive reagents are excluded.
- 🛡️ Isolated. have a plastic cuff (often colored), which not only protects against accidental short circuit, but also serves as a visual indicator of the cross section.
Special attention should be paid to the power tips under the bolt, which have a different configuration of the hole. For automotive wiring, round holes are most relevant, but there are also oval and fork options used in specific mass mounting units or terminal pads. The choice of shape depends on the type of bolt connection used and the available space for installation.
⚠️ Attention: The use of unleaded copper tips in a moist environment leads to rapid oxidation of the contact. The oxide film significantly increases resistance, causing heating of the compound even at standard currents.
Marking and decoding of abbreviations
Understanding the labeling is the first step to a competent selection of components. On the tailings of each quality product by the method of kernation or laser engraving, a code is applied containing information about the material, structure and cross-section. For example, marking TML 50-8-10 It is clearly readable by professionals and does not require additional tables for initial identification.
The first part of the abbreviation indicates the type: TTM means "pipe copper", and the added letter LL It signals the presence of tinder. The numbers in the code are not random, they strictly regulate the geometric parameters of the product. The first digit always indicates the section of the cable in square millimeters for which the tip is intended.
The second numerical value indicates the diameter of the mounting hole under the bolt. This allows you to immediately understand whether the part will fit the existing threaded contact without the need to measure with a rod. The third number, if present, may indicate the diameter of the hole for the pressing or a specific modification of the series.
Table of correspondence of insulation colors and cross-sections
Plastic cuffs on insulated tips often have color-coded cuffs. Red color usually corresponds to sections 0.5-1.5 mm2, blue - 1.5-2.5 mm2, yellow - 4.0-6.0 mm2. However, you should not rely on color alone, as the standards of different manufacturers may differ. Always check the digital marking on the metal part.
Table of size selection by cable cross-section
Correct selection of the size of the sleeve relative to the cross-section of the vein is the key to reliable contact. If the sleeve is too large, even double pressing will not provide the desired density, and the wire will "walk" inside. Too small a diameter will require pruning of the part of the veins, which is unacceptable, as it will lead to overloading of the remaining section and its burnout.
Below is a reference table for the most common in the automotive electric sizes:
| Marking | Cable cross-section (mm2) | Hole diameter (mm) | Application |
|---|---|---|---|
| TML 16-6-8 | 16 | 6.5 | Power circuits, generator |
| TML 25-8-10 | 25 | 8.5 | Starter, AKB. |
| TML 35-10-12 | 35 | 10.5 | Power supply to amplifiers |
| TML 50-12-14 | 50 | 13.0 | Backbone cables |
It is also important to consider the flexibility class of the cable. Conducting classes KG (flexible cable) have more rods of smaller diameter at the same general cross-section than rigid cables. Therefore, the diameter of the inlet sleeve should be calculated taking into account the filling ratio, so that all the veins enter freely, without crevices.
The main rule of selection: the diameter of the inner sleeve of the tip should be as close as possible to the outer diameter of the cleaned beam of the cable, ensuring a tight fit before the start of pressing.
Tools for high-quality installation
To create a non-removable connection, it is not enough just to squeeze the metal with pliers. The quality of the contact directly depends on the effort developed by the tool and the geometry of the profile created. The use of hammer and chisel or ordinary passages is strictly prohibited, since these methods do not guarantee uniform crimping on all sides and can damage the structure of the metal.
Professional installation is performed using hydraulic or mechanical press mites. For automotive tasks, where the sections rarely exceed 70 mm2, manual matrix mites are sufficient. They provide the several tons of force required to plastically deform copper and aluminum, creating cold welding between the veins and the sleeve walls.
- 🛠️ Matrix ticks have replaceable matrices for different sections, form a hexagonal or square profile of the crimping.
- 🔋 Battery tool It allows you to perform large volumes of work with one hand, automatically controlling the pressure force.
- 📏 Instrumentation and measurement - a bar for checking the diameter after crimping and a microohmmeter for measuring the resistance of contact.
It is important that the tool corresponds to the type of tip. For copper products, hexagonal crimping is often used, which provides uniform pressure around the perimeter. Aluminum tips require a more complex profile and the mandatory use of quartz-vaseline lubricant to remove the oxide film during the deformation process.
Technology of pressing of multicore wire
The installation process begins with the preparation of the cable. The insulation shall be removed to a length equal to that of the tubular part of the tip. Excessive removal of insulation will lead to the fact that part of the bare wire will remain outside, creating a risk of short circuit, and insufficient - to the insulation inside the sleeve, which will sharply worsen the contact.
After cleaning the veins, it is recommended to twist your fingers to give them a cylindrical shape, although for high-flexibility multi-core cables this is not always necessary when using a quality tool. Then the wire is inserted into the tip to the point. Visually control that all veins enter the sleeve and none remain stuck outside or fall under the insulating cuff.
☑️ The algorithm of correct repressing
The number of pressures depends on the length of the tail. For short car tips, usually one or two presses are enough. If two pressings are required, the first is performed closer to the bolt hole, and the second is performed at the edge of the cable input. This prevents the wire from being squeezed out when vibrating.
⚠️ Attention: After pressing, be sure to check the connection for break by pulling the wire and tip in different hands. If there is backlash or twisting, the connection is defective and must be remade.
Typical errors and their consequences
One of the most common mistakes is to use a tip of smaller cross-section than a cable, with the pre-removal of the veins. This action reduces the cross-sectional area of the conductor, which leads to its overheating on the site before entering the sleeve. The current passing through the narrowing meets increased resistance, releasing thermal energy.
Another frequent mistake is pressing without removing the insulating cuff at the insulated tips or, conversely, leaving a gap between the insulation of the cable and the edge of the sleeve. In the first case, the plastic enters the deformation zone, disrupting contact. In the second case, bare copper is exposed to moisture and oxidized, especially in the conditions of a winter road with reagents.
Errors include the use of the wrong tool. Cracking the round tip into a trihedral matrix or using a chisel creates stress concentration points where the metal can crack when vibrating. The crack develops over time, the contact weakens, and sparkling occurs.
Useful advice: To protect the entry point of the cable into the tip in conditions of high humidity, use a heat-restrictable tube with a glue layer. It seals the joint and prevents electrolyte or water from entering the sleeve.
Frequently Asked Questions (FAQ)
Can a copper tip be pressed onto an aluminum cable?
Absolutely not. Copper and aluminum have different electrochemical potentials. At the place of their contact in the presence of moisture, a galvanic pair occurs, leading to rapid destruction of aluminum and an increase in resistance. For aluminum cables, there are special aluminium tips or pure aluminum models.
Do I need to squirt a wire before the squirt?
No, you can't lick the wire before installing it in the tip under the pressing. The solder is an alloy that under load "floats" (flows), the contact weakens. In addition, when vibrating, the soldering place inside the sleeve can fracture. Pressure creates a more reliable and vibrating connection due to cold welding.
What to do if there are no press cards at hand?
In an emergency, narrow pliers are allowed, but this is a temporary solution. It is necessary to make several dents around the perimeter of the sleeve, trying to flatten it as much as possible. However, such a connection will not withstand prolonged vibration and high currents, so at the first opportunity it should be replaced with properly pressurized.
How do you know if the tip is overheating?
The main signs are a change in the color of the insulation at the entrance to the sleeve (yellowing, blackening), the appearance of the smell of burning, as well as heating the metal tailings themselves when the consumer works. In advanced cases, copper can oxidize to a greenish or black color.