One of the main conditions for the arrangement of electrical installations in premises of various types and purposes is the grounding system. Together with automatic shutdown equipment, the grounding system can significantly reduce the risk of fire in the event of short circuits. Grounding also significantly reduces the risk of injury. During the installation of any types of installations and electrical equipment, the main grounding bus GZSh according to the PUE must be equipped. What it is? See the answer to this question in our article today.
Design Features
By design, the grounding system is a metal element - one or more. These parts allow you to reliably connect the body of electrical equipment to the ground.
Among the basic parts of this system, it is possible to distinguish the main grounding bus GZSh, the ground wire in the wiring, the tap from the housing, the general circuit. In fact, the circuit is quite simple, but the system should provide the ability to individually connect / disconnect protective conductors in the presence of a special tool. The number of compounds is five or more. It all depends on the selected connection scheme. According to the requirements of GOSTs and PUE (Electrical Installation Rules), every detail of the system must be made of steel (or its alloys) and copper. These requirements apply to any element, regardless of the type of construction of the ground loop and the electrical installation itself.
The main grounding bus GZSh-copper 100x10 is most preferred. This is due to high rates of electrical conductivity, slow oxidative processes when exposed to high voltages, as well as the resistance of copper to corrosion. Steel elements are used only for the purpose of economy. Copper bus is often used in private housekeeping.
The effectiveness of protective circuits is particularly affected by the level of electrical resistance. Among the classic options for connecting to the main grounding bus GZSH, one can distinguish grounding circuits, sewer and water mains.
Installation can be performed by open or closed method. The installation location should be easy to access and maintain. The open type is popular at facilities where access to unauthorized persons is limited. But it is often possible to meet open installation in panel boxes of houses. The closed method is used in panel cabinets - in the boxes of the main grounding bus GZSh.
The effect of resistance on the circuit
The total resistance of the grounding elements is the indicator of each element, conductors, or the entire circuit that is in the ground separately. Often this value is neglected. Metal parts (subject to a high-quality connection), are distinguished by good characteristics of electrical conductivity and low resistance.
Of greatest importance is soil resistance. The smaller this indicator, the more efficient the system. Clause 7.1.101 of the Electrical Installation Rules states that in buildings with 220 or 380 V electrical networks, the resistance should be no higher than 30 Ohms. For generators, as well as for
transformer substation , the resistance level does not exceed 4 Ohms.
In systems that are assembled on the basis of TN-S or TN-C circuits, it is necessary to equalize the potentials in each section of the circuit. For these purposes GZSh is intended.
TN-C
The TN-C circuit has been developed and is still in use since 1913. For the first time, grounding circuits were started to be assembled in Germany in Germany. This type is used in old buildings throughout Europe, as well as in post-Soviet countries. This circuit differs in the way of connecting the neutral conductor. It is connected directly to the ground bus.
If the neutral wire breaks, voltages exceeding phase by 1.7 times can occur on the unit casing. This significantly increases the risk of personal injury.
TN-S
TN-S has been in use since the 1930s. It took into account and eliminated all the disadvantages of the previous connection option. The scheme provides for a separate wire that runs from the grounding system in the substation to the circuit of the grounding system in the building through the GZSH. In the case of a combined connection in separate areas, it is permissible to connect the neutral neutral conductor to the ground line using PE conductors. The electrical circuits of wires from any electrical installations subject to grounding are connected to the GZSH. On it, you can ground the elements of other communications.
PUE requirements
In the rules for the arrangement of electrical installations, in paragraph 1.7.119, all basic requirements regarding the arrangement of the main grounding bus GZSh in networks up to 1 kW are defined. The system is located in the control cabinet of a specific device. In the case of a large number of grounding conductors, installation in a separate additional cabinet is allowed.
For systems implemented on the basis of TN-C, use the PE bus as GZSh. But it should be borne in mind that the PE section should be larger than the wires themselves. It is recommended to use copper to equip the GZSH. Steel is less commonly installed. But aluminum is the grossest mistake. This material is strictly prohibited for use under these conditions.
All connections must be collapsible. Usually they are bolted. The wires are crimped to the lugs and then screwed onto the bus. On the wall next to the last one is sure to put a symbol pointing to the grounding bus.
Clause 1.7.120 defines that for rooms with two or more entries, a separate bus must be equipped. It must be connected with conductors on various switchgears. To connect tires from various devices, metal structures can be used. But only on condition that they are non-separable and have constant electrical contact. At the same time, it is forbidden to use oil / gas / water pipelines, heating systems, cable sheaths, cables and supporting structures of cables as grounding conductors. It is worth paying attention to an important nuance.
This is a common mistake in the arrangement of the main grounding bus GZSh - the rules for the installation of electrical installations (paragraph 1.7.20) allows you to ground these structures to the main bus. However, it is strictly forbidden to connect them directly from different cabinets using these designs. This is indicated in paragraph 1.7.123 of the electrical installation rules.
Specifications
The main grounding bus is necessarily mounted in the electrical panel. Then it connects to the ground loop. Inside the input equipment, tires of the PE type are used. In this case, the conductors must have a certain cross section:
- For copper - 1.1 centimeters and above.
- For aluminum - from 1.7 centimeters or more.
- For steel - from 7.5 centimeters.
The cross-sectional values of the grounding bus should strictly correspond to the type and characteristics of the wire.
Design Features
What is GZSH? This is a copper alloy plate with holes for attaching ferrules. The size of the bus and the number of holes depends on the type and size of the cabinet, as well as on the number of elements and wires that will be grounded. The photo of the GZSH reader can see in this article.
Manufacturers make products in a variety of sizes. For example, the main grounding bus GZSh-21 has a size of 395x310x120 millimeters. It is capable of withstanding currents from 340 to 1525 amperes.
GZSh installation in a case
How it's done? For connection, a PE-type conductor and a box of the main grounding bus GZSh-10 or another are used. The tire should be positioned so that in case of repair there is reliable and safe access to it. Its cross section should not be less than the grounding wire. If necessary, several tires can be connected using standard fasteners.
Cabinets with a bus may be placed on the facade of buildings or in special switchboards. For outdoor or street lighting systems, you can choose a housing with an IP index. Installation includes fixing the bus with a bolted connection in the cabinet, connecting protective elements to the "zero" rail.
Installation outside the cabinet: technology, nuances
External mounting of the strips of the main grounding bus GZSh-10 can be performed in places where there is good protection against unauthorized persons. Fix the element to durable insulators. Among the most convenient options are DIN rails. This is a metal profile that is used in the electrical industry. This rail can be aluminum or galvanized. But now the use of welding is popular. It meets all state standards.
So, we found out what is the main grounding bus GZSh, what requirements it must meet.