What Is an Electrical Connection?

Electrical connection in a broad sense refers to the collection of all electrical circuits in electrical products, including power connection components such as power plugs, power terminals, etc., power cords, internal wires, internal connection components, etc .; in the narrow sense, electrical connections only refer to the interior All ways to connect different conductors.

Electrical connections

Right!

Electrical connection in a broad sense refers to the collection of all electrical circuits in electrical products, including power connection components such as power plugs, power terminals, etc., power cords, internal wires, internal connection components, etc .; in the narrow sense, electrical connections only refer to the interior of the product. All ways to connect different conductors.

Chinese name

Electrical connections

Explanation

A collection of all electrical circuits in an electrical product

Classification

Terminals, PCB connectors, etc.

Application area

Industrial production and infrastructure

Electrical connections include: terminal blocks, PCB connectors, industrial connectors, junction boxes, heavy-duty connectors, cables, cable connectors, safety barriers, contacts, and more. In order to unify the terminology, the electrical connection generally refers to the electrical connection in a narrow sense, and the electrical connection component is used to refer to the electrical connection in a broad sense.

Uses: Electrical connections are widely used in electronics, electrical, industrial production, infrastructure construction, chemicals, ports, machinery, defense, industrial control and other fields.

Generally according to the position of the electrical connection component, the electrical connection component in an electrical product can be divided into two parts: an external electrical connection component and an internal electrical connection component. External electrical connection components refer to all electrical connection components outside the product enclosure (electrical enclosure). Since these electrical connection components are not included in the protection of the product enclosure (electrical enclosure), they must individually meet the corresponding electrical shock protection requirements. Internal electrical connection components refer to all electrical connection components inside the product enclosure (electrical enclosure). Because these electrical connection components are included in the protection of the product enclosure (electrical enclosure), generally only the corresponding functional insulation requirements need to be met. . Take a common rice cooker as an example (see Figure 1). It uses the power line assembly and the power grid connection to provide working power. The power line assembly is connected to the interior of the rice cooker through a coupler, and the coupler is connected to the internal controller through internal wires. (Temperature limiter, thermal fuse) and heating pipe, etc., form an electrical circuit.

General electrical connection components are mainly composed of electrical connection parts (such as terminal blocks, etc.), wires and cables, wire fixing devices and wire protection devices (such as separate wire sheaths, etc.).

The electrical connection component reliably secures different conductor components together by providing an appropriate mechanical force to achieve electrical connection. The key role of electrical connection components is to provide a reliable connection to avoid danger caused by poor contact between different conductors. Electrical connection components usually consist of non-metallic support components and metal connection components. Non-metallic support components are used as the support foundation. In addition to being required to function as insulation during long-term work, they also need to be able to withstand the heat of the conductors supported during use. It will cause dangerous deformation (for thermoplastic materials, it can be verified by ball pressure test), and it has a certain flame resistance rating, and will not become a potential fire source.

Wires and cables as the main current-carrying components, in addition to requiring sufficient current-carrying capacity, also require sufficient mechanical strength and insulation characteristics to meet the requirements of electric shock protection in use.

In order to ensure the long-term validity of the electrical connection, effective measures should generally be taken to avoid excessive mechanical stress on the electrical connection parts of the wires and cables. The usual solution is to use an additional fixing method near the electrical connection to fix the wire and cable, which is commonly known as the "double fixing method" for wire and cable.

The following describes the issues that should be paid attention to when designing external electrical connection components and internal electrical connection components.

Electrical connection external electrical connection components

The common external electrical connection components are mainly the power connection components of the product, and the common power connection components mainly have the following structures.

1. Power plugWire sheathPower cordWire sheathWire fixing deviceInternal power connection structure

This structure is the most commonly used power connection method. When you use it, you only need to plug the product's power plug into a suitable power outlet, and the product can be used normally. In order to ensure safety, the power plug of the product should meet the standards of the corresponding country and region, and match the power outlet of the power grid. In use, you should avoid using power conversion plugs, especially those high-power electrical products. In the market, some conversion plugs even provide only two-pole conversion, and the grounding plug is left floating, which virtually destroys the shock protection system of Class I products and is very dangerous.

2. Power cord assembly (including power plug-wire sheath-power cord-wire sheath-coupler)-coupler-internal power connection structure.

The most significant feature of this structure is that the power cord assembly can be removed easily and freely without affecting the safety characteristics of the product. For example, for some products sold in different countries and regions, especially a large number of IT products, they can often be used in different countries and regions by simply replacing the power cord components, which greatly reduces the product manufacturing process. Inventory pressure. In addition, the power cord assembly can be removed from the product, which can also reduce the volume of the product and improve the comfort of the product.

In order to improve the applicability of the product, most of the couplers adopt a standardized structure (implementation standards IEC 60320, IEC 60309 or equivalent national and regional standards), in order to achieve the interchangeability of the couplers. When selecting a coupler, in addition to considering the specifications and parameters of the coupler, you must also pay attention to the working environment limitations of the coupler. Ordinary couplers are used in cold environments, that is, when the temperature of the pin of the coupler does not exceed 70 ° C. If you need to use the coupler at a higher temperature, you must choose a coupler used in a hot environment or a hot environment.

In addition, many products use non-standard couplers to improve product comfort. Regardless of whether a standard coupler or a non-standard coupler is used, the structure must ensure that the connector of the coupler does not play a supporting role in use. At the same time, the structure of the coupler can ensure that the phase poles are connected at the same time during the connection process, and the ground electrode (if any) is connected before the phase pole; and the structure of the coupler can ensure that the phase poles are disconnected at the same time during the disconnection process. , And the ground electrode (if any) is disconnected after the phase electrode.

3 Power connection terminal block

This type of external electrical connection assembly is generally only used in electrical products using a fixed wiring connection. The characteristic of this connection method is to directly connect the external power cord to the power connection terminal block of the product. The power connection terminal block must clearly and clearly identify the correct wiring method. At the same time, in order to avoid affecting the internal wiring when connecting the external power cord, the external power cord must not share the same port with the internal conductor.

When using products with this connection method, users cannot completely cut off the power of the product by unplugging the power plug. Therefore, the product is generally required to be equipped with an all-pole disconnection device (that is, a switch that can disconnect all power connections at the same time) , And the switch contacts can at least meet the basic insulation requirements), or the installation instructions emphasize that the all-pole disconnection device must be equipped in the fixed wiring.

It should be noted that in the past, many products used for fixed wiring installation did not provide power terminal blocks, but only provided power leads. However, according to the relevant technical safety regulations of many countries and regions, products of this structure are generally not allowed to be sold directly on the market unless a reliable fixed and clearly marked power terminal block is provided.

4 In-line structure

In the case of a product with a direct plug-in structure, the power plug is directly cast on the product's housing, and the entire product is plugged into a power outlet when in use. The products using this structure are characterized by small size and compact structure, but they have high requirements on the production process of the product, especially the tolerance requirements of the power plug part, and must pay attention when designing when inserting the power outlet. There must be sufficient distance between the hand and the socket electrode.

In order to avoid excessive mechanical stress on the socket during use (the additional torque generated on the socket is generally required to be less than 0.25Nm), the mass of the product's direct insertion part is generally within 500g. Common in-line products include small power adapters and chargers. In addition, in-line products require no vibration during use. Therefore, products of this structure cannot usually be used directly to heat liquids or have electrical parts.

Electrical connection internal electrical connection components

Internal electrical connection components include power supply terminals, various internal electrical connection components, internal wires and their sheaths, etc. As for windings, they are generally not considered to be included in the scope of internal electrical connection components, but printed circuit boards can be considered as one A special internal electrical connection component.

There are many types of internal electrical connection components, which can be various threaded or non-threaded terminal blocks, various connectors, and even connection components such as crimp connection, winding, and welding.

The power terminal is a terminal for connecting an external power cord. If the product allows the power cord to be replaced as required, then the power cord terminal is usually in the form of a terminal block (either threaded or unthreaded), and the correct wiring should be clearly and clearly marked next to the terminal block; At the same time, in order to avoid affecting the internal wiring when connecting the external power line, the external power line is not allowed to share the same port with the internal wires. In addition, in order to avoid the danger of electric shock when the power line fixing device fails, for Class I electrical products, once the power line is pulled out by external force, the phase line should be tightened and detached before the ground line.

As for the inner conductor, it is also necessary to select a conductor with an appropriate cross-sectional area according to the magnitude of the working current. The internal cross-sectional area can be selected according to the actual working current and does not necessarily need to be the same as the cross-sectional area of the power cord. In the actual production and assembly process, in order to avoid confusing wires with different cross-sections, some factories usually use different colors to distinguish the wires with different cross-sections. At this time, it is necessary to pay attention to the two-color identification wires with a yellow-green combination. Ground lead. When selecting internal wires, you should also pay attention that aluminum wires should generally not be used.

Because the inner wires are under the protection of the shell, the requirements on mechanical strength and insulation are lower than those of the external power wires. Basically insulated wires and even bare wires are allowed in certain circumstances. It should be noted that due to wiring and other reasons (such as the wires connecting different parts of the product), the wires that are exposed and can be touched during use, although they are called internal wires (as opposed to power wires) in many cases, but In the field of product safety, these wires are also part of the external electrical connection components because they are not protected by the housing, and should be referred to the power cord unless they are safety extra-low voltage (SELV) circuits.

In the structural arrangement of internal wiring, the following points should be noted.

The internal wires should be effectively fixed. It is common to fix multiple internal wires together with a cable tie, but the heat resistance and aging of the cable tie must be paid attention to.

The exposed internal wiring must be rigid and securely fixed by mechanical means. It is impossible to shift in normal use to prevent the short-circuit or electric shock caused by the creepage distance and too small electrical clearance.

Prevent the wires from coming into contact with the moving parts, and avoid the moving parts from scratching and wiping the wires and damaging the insulation of the wires. For wires that may come into contact with sharp edges and edges, an extra sheath should be provided to avoid damage to the insulation of the wires due to movement, vibration, etc. during normal use.

The internal wires should be kept away from the heat source, and the temperature of the environment around the wires should not exceed the allowed temperature range of the wires. For the wires near the heat source, appropriate high temperature resistant wires should be selected or appropriate insulation measures should be taken, such as using heat-resistant sleeves.

The printed circuit board can be considered as a special type of internal electrical connection component, but because the printed circuit board relies on copper foil for electrical connection, the current carrying capacity of the printed circuit board is not strong, which is in the design Full attention must be paid when doing so.

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There are two common issues in internal electrical connections that require special attention.

One problem is the problem of welding reliability. In addition to paying attention to traditional process issues such as false welding, attention must be paid to the effect of welding on multiple strands of flexible wires. After welding of multi-stranded flexible wires, the solidified part of the solder cannot remain as flexible as before. Therefore, the flexible wires will gradually break at the welding junction due to mechanical stress and vibration. Therefore, the fixation of multi-stranded flexible wires is generally Do not rely on welding. At the same time, in order to avoid the free movement of the disconnected wires and affect the internal clearances and creepage distances, additional fixing devices should be provided near the welded parts of the multiple-stranded flexible wires. For example, heat shrink tubing can be used to secure both wire insulation and solder joints. In short, minimize the stress on the welding junction. For some cases where there are perforations at the soldering end, as long as the perforations through which the wire passes are not too large, in addition to foil wires, hooking into the perforations before welding is also a suitable method. As for welding after winding, the welded part should be at the top so that the wound part can play an additional fixing role.

In addition, attention should be paid to the restrictions on lead content in solder in many countries and regions in recent years. More and more soldering has adopted the lead-free soldering process, but the process requirements are relatively high, and the possible "tin whiskers" will affect the electrical clearance, creepage distance, etc. This is a key issue that needs attention in the field of electrical product safety in the future.

Another problem is the problem of pressure transmission in electrical connections. Generally, in order to maintain the reliability of the contact and ensure the current carrying capacity of the circuit, especially for situations where the current passed exceeds 0.5A, the contact pressure of electrical connections (including connections that provide protective ground continuity) should not rely on easy contraction or deformation Insulation material to retain and transfer, unless it is a ceramic material. Using springy metal parts for pressure compensation is an effective method in practice.