Terminal boxesEach of us at least once paid attention to the boxes or "hatches" under the ceiling and knows that the wires are located there. If you repaired house wiring or just looked into these hatches, then you know a little more - there are wires twisted between them.


  • 1 What are junction boxes for?
  • 2 Reliability junction box
  • 3 What devices are
  • 4 Wire Connection Types
  • 5 What type of connection is better to use
    • 5.1 Junction box selection criteria

What are junction boxes for?

What are the boxes for?The junction box (it’s also a junction box, a terminal box, and even a terminal box with terminals) really serves for wire connections, but not to simply splice them, making them longer, and to assemble an electrical wiring diagram on limited area. For example, the room has an outlet, a chandelier and a switch for it. All this electrical equipment must be connected to the switchboard located at the entrance. The actions are obvious: one wire is pulled to the socket, the second to the light bulb, and a switch hits in the middle of the last. But you can do this:

An example of wiring diagram apartment wiring

From the meter, hanging in the stairwell, laid power wire in the corridor. There is installed the main junction box (1). From it is done wiring to each of the rooms, including our with a chandelier. One more box (2) is installed in the room and individual wires from each of the consumers - lamps and sockets - as well as from the switch are brought to it.

What does such a scheme give? First, the wires for assembling the electrical circuit will go significantly less, especially if you have four sockets, a three-hinged chandelier, three wall sconces and four switches. After all, all the lamps and sockets of the same room will be fed through one lead wire laid to the room distribution box.

Box reliabilitySecondly, a similar design is much easier to defect in case of a malfunction. If, say, your chandelier has gone out, all you have to do is get into the room junction box and in one way or another. (for example, by dialing a de-energized line or by indicating the voltage when the line is connected), calculate the damaged plot. Everything is in order (more precisely, the disorder is not here) - you move through the boxes towards the electric meter.

And, thirdly, this is the main thing - to repair such a scheme is much easier. You do not need to spread almost the entire apartment, tearing off the wallpaper and tearing out the burnt wire with plaster. Then make a new strobe, lay a new wire, gloss over, paint, glue. Restoring power to even the furthest outlet will be limited to a light one-room pogrom to the nearest junction box.

The use of switchgears not only facilitates installation, but also makes it vivid and maintainable.

Reliability junction box

Assembly boxes.When considering such a scheme, the question immediately arises: how will the use of boxes affect the reliability of the whole structure? So many connections, and even so on one wire so many consumers... That is why there is a perception that the distribution box is evil.

It is worth a little to disappoint the skeptics. With properly selected junction boxes and types of connection of wires of the corresponding cross section, reliability will hardly suffer. It will somewhat decrease with, say, a flood from above (the boxes will flood with water), but, first, this situation is abnormal, and second, the right connection will not survive. Well, if you specifically floods regularly, you can use special waterproof junction boxes with terminals. And in general, even if the reliability of electrical wiring decreases by a few percent, it’s worth it, because you don’t will have to carry the whole house to find the slightest malfunction, and then finally demolish that malfunction eliminate.

What devices are

Modern devices are of two types:

  1. Internal or hidden.
  2. External or overhead.

Terminal boxes for concealed wiring (right) and surface type

Types of wiring boxesThe former are used, as a rule, for the installation of concealed wiring, the latter - for outdoor. The material for their manufacture uses the most diverse - from ordinary or non-combustible plastic to metal. The latter are recommended to be grounded, although this is often not done out of laziness or negligence. Both those and others can have both usual execution, and waterproof or even tight. The latter two are used in high-risk premises - damp and explosive (basements, warehouses, ships, etc.). Differences between internal and external boxes are not only aesthetics, but also ease of installation. For example, it is much easier to use internal distributors for concealed wiring.

Wire Connection Types

This is perhaps the main point that affects the reliability of the entire circuit. Usually for connecting the wires are used:

  • Junction boxesTwist.
  • Spike
  • Welding.
  • Swage.
  • Terminal blocks under the screw.
  • Clamping and self-clamping terminals.

Coupling with self-locking blockTwisting is considered the most unreliable method of joining, but, nevertheless, if twisting is performed quality, and the material of the wires is homogeneous, then such a connection is quite acceptable and will stand decades. Of course, over time, the wires oxidize, and due to poor contact of the site, twists begin to warm up. They get hotter - oxidize faster. Stronger oxidation - even more heated. The result of such a process is understandable - burning out the compound at best. At worst - a fire. If the wires are made of dissimilar metals (say, aluminum and copper), then they can not be twisted at all. They are a galvanic couple and oxidize very quickly when current flows.

Twist Connection

Spike Very good method, but requires an electrician ability to work with a soldering iron. In addition, some materials (the same aluminum) are soldered very reluctantly and require special fluxes. Well, the last "against" - not always on the object there is at least one outlet under voltage.

Conventional soldering

How to connect the wiresWelding. Exceptionally reliable method. The wires are twisted, and then the end of the twist is fused using a special torch or an electric arc. There are two drawbacks to this method - you need special equipment + skills, and when using arc welding, there is also a plug socket under voltage. In addition, to weld between each other dissimilar metals is very problematic, and often impossible due to the difference in melting temperatures (the same copper and aluminum).

Connection by welding

Swage. The essence of the method is as follows. Two wires are connected by twisting, a cylindrical sleeve is put on top, which with the help of a special tools or improvised means (the same hammer with an improvised anvil) is crimped, reliably fixing compound. The material of the sleeve is usually taken the same as for wires. If you need to connect dissimilar metals, the iron sleeve is taken, and the wires do not twist, but are located in the sleeve one opposite the other. Crimp the wires with one sleeve, but separately each.

Crimping connection

Block under the screw. Some boxes are composed of pads in which the connection of wires can be made with a screwdriver, tightening them under the screw (as in a socket or switch). Such a connection is quite reliable and will last for a year, if you, of course, tighten the terminal screws properly. By “properly” is meant not “as much as possible”, but “strongly within reasonable limits.” Otherwise, you simply pass the wire with a screw or break the thread.

Screw terminal connection

Clamp block Clamp pad. Here, instead of the screw, a springy “toothed” contact is used, equipped with a pressure bar. Click on the bar, insert the wire into a special hole, release the bar. The teeth of the terminal literally dig into the wire, ensuring reliable contact. This connection is convenient for installation, can be used to connect stranded wires, but does not hold current load. If you are not going to mount high-current circuits, then, in principle, such a connection is suitable.

Clamping block

Self-tightening pads. These pads do not require any effort on your part. They work on the principle of "stuck-not-poke out." Strip the wire and insert it into the hole in the pad. A special spring ensures reliable contact, and the “toothed” part of the clamp prevents spontaneous disconnection. The disadvantages of this type of clips are their one-timeness (it is often impossible to pull the wire out of such a pad without damaging the terminal itself) and the relatively low load current. Such devices are very convenient for the quick installation of low-power equipment - chandeliers, fans, etc. - especially if the installation is made with stranded wire. For the distribution box, it can be considered not entirely successful, as the previous one.

Self-locking connector

What type of connection is better to use

It all depends on your skills, capabilities and the required reliability and durability of the connection. Practically all of them, except for the last two, with properly performed work, meet these requirements. The most reliable connection, of course, is welding. Then go soldering, crimping, tightening under the screw, twisting and, finally, clamping and self-tightening terminals.

Junction box selection criteria

When choosing a junction box, consider the following criteria:

  1. Box mounting featuresType of device. First of all, decide which boxes you need - hidden or overhead. If the wiring is hidden, and the recesses in the wall under the distributor are real, then, of course, hidden boxes are preferable. They practically do not spoil the interior, and it is easy to get the wires recessed into the grooves in them. If the wiring is external, then the boxes must be overhead.
  2. Dimensions. Just think in advance how many connections will be in the distributor, what type they will be. Based on this and be guided by the size and shape (round, square). If everything fits into a small box, then installation, and later repair, will be difficult. An excessively large box - extra work on the destruction of the walls (hidden construction) and terrible aesthetics (surface construction).
  3. Material. If you do not put the box at the level of a kick (shoulder, elbow, bucket in hand, etc.) that you can accidentally break it with, then there is not much difference. It all depends on your personal preferences, tastes and financial capabilities.
  4. The method of connecting wires. This is the most important point, but it was considered above. The only thing is, if you do not find a device with a block for the desired number of wires, you can buy a regular empty box of a suitable size, and just buy the terminal blocks of the desired type separately.

Junction boxes are large and small, round and square, plastic and metal, with or without terminals. How to choose - you decide, based on specific conditions, skills and capabilities.