When arranging underground power lines that require difficult operating conditions, armored cables of the AVBBSHV type, common in electrical engineering, are traditionally used. Their distinguishing feature is the presence of a protective shell consisting of lead, which is called armor. A prerequisite for their safe operation is the grounding of the armored cable, organized according to standard rules. For these purposes, both station and repeated grounding devices are used, which are equipped on the consumer side.
What to ground
When wiring armored cable lines, the following structural parts and braid elements are subject to mandatory grounding:
- armor and shield of power and control cables;
- special couplings;
- elements of metal products used for laying: trays, boxes and similar structures;
- metal pipes used for the same purpose;
- special suspension cables for aerial installation of power lines.
According to the requirements of the PUE, each of the ends of the cable line, spaced at significant distances, is supposed to be grounded. The regulations specifically note that sections of electric lines longer than 200 meters are subject to repeated grounding.
Basic grounding rules
The PUE pays special attention to grounding the cable armor on both sides, since only in this case can one be sure of its absolute reliability. When organizing such work, the following details are taken into account:
- for grounding the armor of cable products, flexible conductors based on copper, without insulation, are used;
- throughout the laying, continuous coating breaks are not allowed, it should be solid;
- when restoring the damaged line of the sheath of individual sections and the coupling must be connected by flexible conductors.
But first, these parts should be carefully prepared for installation work.
Grounding instruction
When grounding an armored cable, PUEs are recommended to act in compliance with the following rules:
- The ground conductor is attached to the cable armor by soldering.
- First, this place is thoroughly crowded, after which a grounding conductor with the mandatory use of solder grease is soldered to it using a wire brace.
- To connect the copper outlet without soldering, special clamps are used.
For these purposes, it is also allowed to use spring-loaded connectors that guarantee reliable contact with the protective layer.
In the case of tape armor, the ground wire is attached directly to its branches, and with wire braiding, it is circumferentially connected to all its conductors. When connecting cable lengths of standard length, hermetic couplings of a special design are used. Connector kit includes:
- local elements of waterproofing;
- tips with special bolts;
- ground wire fixed to the armor of the connected sections;
- clamps for attaching wires with armor made of wire or steel strips.
When cutting the cable before arranging the contact, the upper insulating layer is removed to a length slightly larger than the braid located under it. In some types of couplings, the manufacturer provides a special template that guarantees high-quality cutting of the entire product.
Grounding inside a private house
According to the PUE, the following rules must be observed when grounding the cable armor in a domestic environment:
- 0.4 kV armored cable is allowed to be laid in metal structures, reliably grounded and available for repair and maintenance;
- laying on concrete floors and wooden flooring is performed with a gap of at least 5 cm, for this metal boxes and special supports are used;
- Entrance to the house is allowed to be done both through the floors, and through a specially designated area of the wall.
In order to prevent damage at the entrance to the building in places of wiring through walls or a foundation foundation, the cable is laid in a pipe made of metal or plastic.
The diameter of the pipe segment is selected 2 times larger than the cross section of the cable product itself.
When the line is entered into the house, the armor is grounded in the switchboard, as well as from the side of the outlet support. According to the PUE, no other connections on this section of the route are allowed. At the input, the cable is divided into several cores connected to switching devices; while its armor is necessarily connected to the grounded point of the shield body - directly to the ground.
Ground cable underground cable
To obtain high-quality grounding of the cable screen, PUE recommend that you adhere to the following rules:
- Cable armor and protective structures (structures) used for their laying should be connected with elements of grounding conductors of any type.
- The connection is formed due to reliable contact with the exposed parts of metal pipes, reinforcing bars and other elements of natural grounding conductors.
- When organizing a power supply network in a private house, the armor of the introduced VbBShv underground cable is connected to the re-grounding device.
When wiring control and optical cables, grounding of at least one of their ends is considered mandatory.
For signal lines, grounding is done to reduce the influence of electromagnetic fields on the streams of transmitted data or to completely eliminate it. For particularly important areas of information exchange, a two-way earth fault is arranged. The screen of such cables is connected to the GZSH of the junction boxes by means of copper conductors with a cross section of at least 4 square meters. millimeters.
Conductor Requirements
With a grounding device, as well as protective grounding, the steel sheaths of cables of any class or armor is connected to the memory by means of standard sized copper conductors. This requirement also applies to cases of couplings or terminations. On lines designed to transmit high-voltage power (6 kV and above) and having an aluminum sheath, clutch groundings are made by separate conductors.
For this, copper conductors with conductivity greater than the corresponding value for cable sheaths are prohibited.
The general requirements of current standards provide for the use of bare copper conductors with a cross section of at least 6 mm square. The same parameters for control cables are specially stipulated in the PUE (see items 1.7.76-1.7.78).
If end couplings containing surge arresters in their kit are provided on the air supply support for the electrical installation, their housings are connected directly to the memory of protective devices. The use of cable sheaths alone in this quality is not allowed in this situation. Special flyovers and galleries used for placing cables in explosive execution are necessarily equipped with protection against lightning discharges and lightning.
When switching from an underground laying line to a section of its aerial wiring and if the reinforced concrete support does not have its own memory coupling, it is allowed to ground to the cable armor.Such an approach is permissible only provided that the repair or extension sleeve at its other end is connected to the station grounding loop, or if the resistance value of the sheath of the grounding cable is sufficiently small.
When laying underground communications on the basis of armored cable products, the efficiency of their operation largely depends on the quality of grounding of the protective sheath. When conducting electrical work of any complexity, this issue is given increased attention.
