When installing electrical panels, prefabricated connecting jumpers of various designs are used to combine the line of automatic machines or RCDs. A 3-phase distribution busbar is one of these elements used in equipping 380 Volt power cabinets. Connectors of this type provide a reliable combination of several 3-pole or 4-pole circuit breakers in an electrical panel and can do without the tedious installation of jumpers from copper conductors.
Connection rail design
Unlike single-pole devices, where they are connected via one phase contact, the design of the three-phase connection bus has four insulated combs with fixed pins. With their help, phase contacts are connected on 3 and 4 pole circuit breakers, as well as on residual current circuit breakers rated for 380 volts. The fourth row is used to combine the zero terminals when disconnecting several group or linear RCDs.
When carrying out similar operations in 3-pole machines, where only the phases are brought in, the contact taps of the fourth connecting row simply bend.
When installing instead of two protective devices, a 4-pole differential circuit breaker completely replacing them, comb outlets are connected to all the contacts involved in the circuit.
Known examples of three-phase bus connectors have designs that differ in the pitch between the taps in each of the 4 rows (18 mm and 27 mm). The first of them is in demand when combining automatic machines in a single-module design: the total number of occupied seats is 3 or 4. The second, more rare variety is selected with a case width of 1.5 modules: occupied length - 4.5 or 6 seats. The design of copper busbars allows you to install a package of machines with a total number of pins from 12 to 60 pieces.
To acquire combs if it is necessary to install a small number of 3-phase protective devices does not make sense. Usually they are in demand in the installation of switchboards with a large number of machines, RCDs and other switching devices.
When getting acquainted with the design of a copper rail, it is also important to take into account its working section, which, according to the standards, should be at least 16 square meters. mm Confirmation of the effectiveness of the use of these electrical products is an approximate calculation of the volume of conductors saved when using tires.
Types of bends
Two types of connecting contacts of copper busbars are known, which differ in their design and installation features.
- Connectors made in the form of pins and having the generally accepted designation "Pin". These products are suitable for the vast majority of models of automatic devices.
- Fork type bends marked “Fork”.
The second variety is rarely used in domestic conditions, which is explained by special requirements for its installation. For reliable fixation of such taps, a special clamp is required, which is not provided for in the configuration of most connected AVs. Regardless of the type of outlet pins, their cross section is selected from the calculation so that the copper material does not overheat at operating currents up to 63-100 amperes inclusive.
When choosing three-phase buses that differ in the type of connecting taps, the design features of the machine itself are taken into account. For each set of devices to be combined on a DIN rail, quite specific brands of combs are suitable.If you try to arrange the connection using a ridge, the bends of which do not correspond to these devices, they will not fully enter the locking sockets. In this case, a small part of the plane of the shank will remain open for touch.
According to the PUE, the presence of parts of the comb that are not protected by insulation is a violation of safety requirements.
As an example of the use of tires of various classes, circuit breakers of the ABB brand are considered, which are traditionally produced in two different designs. The first of them are designated as "S200". They are designed to install a PSH type bus. For devices of the second class, marked as "S200L", combs under the designation PS are required.
Experts note that Chinese tire products with typical bends in size and pitch sometimes do not interfere with automatic machines from other foreign and domestic manufacturers. Therefore, professional electricians are advised to purchase them only after consulting with specialists in electrical engineering.
Advantages and disadvantages
The advantages of using a 3-phase bus made of copper connectors are:
- simplicity of design, significantly reducing the installation time of the entire control cabinet;
- reliable electrical contact between the terminals of the individual modules;
- a double reduction in the number of connections, significantly increasing the operational reliability of the entire structure.
The latter is explained by the fact that when installing typical wire jumpers on one phase clamp, two contact ends are cleared of insulation. When using a three-phase comb, only one tap is connected to each of the phases.
The disadvantages of the use of such connectors include:
- inconvenience of updating three-phase machines or RCDs, since in this case you will have to remove the entire comb;
- the impossibility of increasing the total number of devices in the line. For this, a larger dimension tire is required.
- during installation, it will be necessary to select the same type of automatic machines, since the same comb may simply not be suitable for different devices.
Professionals offer a simple solution to the problem of adding new devices to existing samples on a din-rail. To do this, install in advance a couple of redundant devices with the most “running” ratings of 16 and 25 Amperes on the mounting bracket and connect only their upper contacts (the lower terminals will remain in reserve). All this time, the switching mechanisms of the machines remain off.
If you urgently needed to use another device, it is enough to connect a new load to its three lower contacts.
Tire Installation and Maintenance
Mounting a three-phase bus is quite simple, however, when installing it, you will need to take into account some nuances.
During installation, it happens that the non-insulated part of the comb does not fully enter the contact crimps. To avoid this violation, the plastic insulator in its design, slightly protruding outward, will need to be positioned with a ledge in the direction of the screw mount. If this is not done, it will result in a not very neat connection with a partially exposed plane, devoid of smoothness of the bending lines.
When installing 3-phase combs, the location of the insulators is given special attention, since violation of this rule is fraught with dangerous interphase faults.
When installing connecting buses that combine the terminals of the RCD and three-phase machines, it is imperative that the marking specified in the standards is observed. It is available on the instrument housings and indicates the phase order.
The combs come into open sale in the form of rulers, already measured in a standard size with a different number of mounting stud contacts. Immediately before connecting three-phase machines, their total number is calculated and, taking into account the thickness of the module, the excess is cut off from the bus.Situations are possible when devices of a different class (three-phase 3-pole AV and 4-pole RCDs) are combined in one cabinet in the same cabinet. The installation of copper jumpers in this case is somewhat complicated, since in the area of the connection to the machines their spikes will need to be slightly bent to the side.
During the preventive examination of the elements of control cabinets, special attention is paid to the connecting busbars in the place of fixing their taps in the slots of the machines. Over time, from significant current loads in the contact zone, the metal heats up, which manifests itself in the formation of a characteristic darkening. During long-term operation, this place is simply charred and covered with black soot, which often leads to thinning and a sharp decrease in the conductivity of the jumpers.
To avoid the unpleasant consequences of burning, you will need to replace the copper bus, for which you will have to completely dismantle it. Due to the design features of the connecting dies, it is not possible to replace one of the 3 or 4 rails. In this case, you have to change the entire product assembly.
A connecting three-phase comb used to combine circuit breakers and RCDs at the input is a very reliable way to obtain a single structural unit. Rulers of several different types of modules with a reliable connection bus are installed not only in enclosed switchboards. This design can be mounted in any other place inside the house, well protected from the weather and reserved specifically for these purposes.
