Zero bus - a terminal block designed for electrical and mechanical connection of zero protective "PE", working "N" and phase network elements. Used for the correct organization of wiring in distribution boards or junction boxes. Installation of the protective system is carried out on a DIN rail, electrical panel, corner insulators.
Why are different grounding systems used?
What is the zero bus for?
The terminal block solves a number of tasks:
- Fast and reliable connection of single-core, multi-core cables supplying loads. The bus allows a maximum of 40 lines with a cross section of 3 mm to be connected.
- Formation of an unbreakable electrical circuit on the "ground - load" segment.
- Separation of wires into protective and working ground.
- Improving the efficiency of switchboards.
Special attention should be paid to the possibility of organizing a visible terminal when installing a device with a transparent cover, which makes it possible to ground and neutralize the conductors on the corresponding buses.
What are zero tires
Zero bars for mounting on a metal DIN rail, G-rail or panel board are insulated and without additional protection. The terminal is insulated with a flat PVC base or a strip equipped with two polymer "legs" (for example, ШНИ-6х9-6-У2-Ж from IEK). The bar is attached to the insulator in the center or along the edges.
In areas requiring additional protection or the connection of several conductors: N "zero", PE "earth", PEN "earth-zero", we can use a polymer housing offered in various colors: blue for neutral, yellow or green for grounding.
Design features
The construction of the zero bus is represented by a metal bar with holes and clamping contacts (bolts), which increase the safety of wiring. The functions of the conductors are performed by copper, bronze, brass elements, the insulator is polyamide, which does not support combustion. The monolithic design of the product simplifies maintenance, increases the reliability of fixation.
Zero Bus Characteristics
Non-insulated zero bus with sides 6 * 9mm and 8 * 12mm, lengths 0.5 and 1 m differ in two ways of connecting conductors: in the center or at the edges of the product.
The zero bus is insulated with two polymer "paws" for attachment to the panel; it feeds the wires through the upper, side holes. Sizes of bars (width / height): 6 * 9 and 8 * 12 mm.
The zero bus HCD has universal fastenings: on the Din-rail and on the surface of the shield at the same time. The basic dimensions of a metal bar are 6 * 9 mm and 8 * 12 mm.
Zero rail with CD insulator is mounted on a Din-rail in the center of the product. Terminal dimensions 6 * 9mm, 1 m.
The cross-module is represented by a zero rail in a housing for mounting in a panel or 2-4 conductors in a polymer box, fixed on a DIN rail or flat surface through the holes on the rear panel. The device contains holes of various diameters, allowing you to connect wires of appropriate cross-sections.
The permissible current for the use of the cross-module in the mains is 100-125 A, the rated voltage is 500V.
Installation rules
Installation of the simplest terminal to the panel is performed in a closed and open way. The first option prevents malicious damage to the bus of powerful or important devices, the second method is applicable when there is no risk of damage to the device. Zero blocks with screw connections are fixed to a distribution board on a DIN rail, no additional insulation for grounding is provided.
The cross-section of neutral and phase conductors is the same. A similar requirement applies to the parameters of the tire: the size of the thinnest sections is considered the actual cross-section. When combining a group of ground and zero conductors, the end consumers, after separating the "PEN" input, are connected to different buses: PE and N.
The permissible range of external temperature for mounting conductors is -40 ... + 50 ° С, relative humidity - 90%. The rated voltage on the line is more than 400V.
What to do if the required zero tires are not available
Often imported distribution cabinets (ABB Mistral) are equipped with one bus "N" and "P", and if an electrician plans to ground three RCDs, he will need 3 small blocks instead of one big one. Since the dimensions of the branded shields, insulated boxes exclude the placement of conventional tires, installers have to saw the existing plank or buy according to an individual order. Having immersed the resulting products in a plastic case, it remains to check the stability of the fastening of the brass pieces.
The grounding bus on the Din-rail is attached separately from the zero block; the use of a common terminal is prohibited.
How to connect several machines
The choice of the scheme is determined by the characteristics of a particular electrical network. The easiest way is to install one RCD immediately after the meter. A safer option is to connect protective devices on individual lines. If one device fails, the rest will remain operational. The implementation of the second scheme requires the use of a side panel.
Simple circuit
Using an example, it is convenient to consider a single-phase circuit used for most apartments in multi-storey buildings. A two-pole automatic switch is installed at the entrance, which connects the RCD. Bus "0" in the electrical panel is marked with "N". The two-pole residual current device is connected to two single-pole circuit breakers. The output of individual machines allows loads to be connected in parallel.
The phase connected to the automatic switching device enters the RCD input with output to the circuit breakers. The zero output from the machine is directed to the corresponding bus, then to the input of the connected device. The neutral wire leaving the consumer equipment is directed to the second zero terminal. The presence of an additional bus "0" allows the RCD to control the input and output voltage.
If two RCDs are connected, three brass blocks are required: the main zero bus with marking N1 and bars N2, N3 for residual current devices. The RCD is grounded to an additional element of the electrical panel - the "P" bus.
Three-phase network
Special networks include a three-phase RCD for 8 contacts or three single-phase. The principle of connection is the same, but phases A, B and C supply loads at 380 V.
Single-phase RCDs with two poles are connected on the outgoing branches. To cover the leakage current in the range of 10-30 mA, separate machines are inserted in front of the RCD. However, in the circuit after the RCD, it is not allowed to connect the working zero and ground.
Which manufacturer to choose
If the RCD, wiring, switches are made by IEK, ABB, Legrand or Schneider Elerctric - it makes sense to buy zero and earthing strips of the same brand. Extremely cheap "N" (zero) tires increase the likelihood of breakdowns that cause problems for expensive electrical appliances.
Bus "0" and grounding are present in new houses connected to a three-phase network. Old buildings have a phase and zero, ground the load with a third conductor to the sockets, and then to the ceiling to the point where the chandelier is connected. Switches are not supplied with ground.
Installation of protection systems for single-phase and three-phase networks requires taking into account many parameters; the right decision would be to entrust the calculation and installation of zero and grounding buses to qualified specialists.
