Deaf-grounded neutral: principle of operation, diagram, application

A deafly grounded neutral is the basis of the power supply system of consumers, it is aimed at the safe use of networks up to 1000 Volts, which are most often used in everyday life and at work as a source of standard low-voltage voltage. The neutral, in turn, is the common point of connection of the windings with a star at power sources, which are transformers or generators. If you connect this point to the ground, then you get a network with a solidly grounded neutral. At the zero point, potential equalization occurs, which is very convenient for providing electricity to both single-phase and three-phase sources.

The device and principle of operation of networks with a dead-grounded neutral

The principle of operation of power sources, in particular, step-down transformers, is based on the law of mutual induction and energy transfer through the magnetic core. At the same time, the primary winding may not have a neutral wire, unlike the secondary, where its connection to zero through a conductor with low resistance, which can be equated with zero value, will be an effective means of protection against injury to a person dangerous to his life and health tension.

The main feature of networks with a grounded neutral is the appearance of not only linear, but also phase voltage. What it is and how it differs from each other, let us consider using a simple schematic diagram as an example.

Phase voltage is the potential between one of the line wires and a zero point connected to earth, that is, tightly grounded. Line voltage is the potential difference between the two terminals of the lines, that is, L1 and L2, L1-L3, or L2-L3, it is also called phase-to-phase. Such sources of electrical energy in domestic conditions have a common voltage value in the form of 380 V - linear, and 220 - phase. The line voltage is greater than the phase voltage by √3, that is, by 1.72.

But the main task of such a system is not only the transportation to the consumer of two power supply systems with different ratings and different the number of phases, but also the protection of a person in case of insulation breakdown and the appearance of voltage at points that in a normal state do not have a dangerous potential. In residential buildings, these are:

• housings of all household appliances that conduct electric current, that is, made of steel or other conductive metal;
• metal structures of switchboards and switchgears;
• protective sheath of cables.

Also, to ensure safety, all of the above elements must be grounded, in this case the danger from the use of voltage and the use of household appliances in networks with a solidly grounded neutral will is minimal. Moreover, for such circuits, the uniformity of the distribution of single-phase loads is mandatory.

Explanation for dummies

The step-down substation in which the transformer is installed has its own ground loop. It is interconnected by steel busbars and rods, into one earthing loop. A cable is laid to consumers in the electrical panel from the substation, which contains four cores. If the consumer needs power from a 380 Volt three-phase circuit, then it is necessary to connect to all cores. In a single-phase 220 V network, power will be provided from the neutral wire and from one of the phases. Protection of people in single-phase and three-phase circuits, if there is no grounding system, should be carried out by means of special residual current devices (RCD), which operate with a small leakage to zero, while reliably disconnecting the consumer from the network.

Classification of networks with grounded neutral

The modern power supply system has a standard marking where, in addition to the working neutral conductor, there is also a protective one, which determines the degree of security.

• L - phase conductor;
• N - working zero;
• PE - protective neutral conductor;
• PEN - working and neutral conductors are made with one wire.

There are several subsystems in circuits with an energy source that has a solidly grounded neutral:

• TN-C. With this system, the neutral and protective conductors from the substation are organized by one conductor, near the receiver it the case (or other elements to be grounded) are connected to this combined conductor - this is called grounding. This is an outdated system that was used in old houses in the USSR, now it is not used for household consumers, as it is unsafe. Such a system has a significant drawback, since in the event of a break in the PEN conductor on the way from the supply transformer to the electricity receiver, a dangerous potential. Used only to protect industrial consumers (discussed below in the next section).
• TN-S. Has a greater percentage of safety during emergencies. This is achieved by separating the protective and working conductors along the entire length of the supply line, from the transformer to the switchboard (to the end user). However, due to the fact that it is necessary to use cable products with five cores, which greatly increases the cost of laying and the budget for organizing power supply to the consumer, this system is not applied always.
• TN-C-S. This grounding system is the most common in our time. With this system, the neutral and protective conductors are combined along the entire length of the line into one combined PEN conductor. At the entrance to the building, this conductor is divided into protective PE and zero N, which are further distributed among consumers (apartments). With this system, if the PEN conductor burns out to the separation point, a dangerous potential will appear on the grounded enclosures of electrical appliances. To prevent this, the PEN conductor is re-grounded along the entire length of the line and at the entrance to the building, and increased requirements are imposed on the mechanical protection of this conductor.
• TT. This grounding system is practiced when the TN-C-S system line is in unsatisfactory technical condition and insufficient safety provided for in it protective grounding. This grounding system provides for the installation of an individual ground loop at the consumer, while the PEN conductor of the electrical network is used only as a neutral conductor N.

It's important to know

For power supply of single-phase and three-phase consumers in industry and in domestic conditions, the so-called vanishing, which "supposedly" is an effective method that provides automatic shutdown of an electrical installation or part of it, in which a short circuit has occurred. When grounding in circuits with a dead-grounded neutral, all metal parts and housings of electrical equipment are connected to the neutral wire. How does this protection work? The fact is that with any short circuit to the case, the circuit goes into short circuit mode, the current in the circuit breaker circuit increases greatly and the emergency section is disconnected from the network.

The advantage of such a system is the savings in the cost of wiring protective grounding, as well as a decrease in the cost of cable products, since both single-phase and three-phase can be connected to the same circuit electrical receivers.

However, the disadvantage of a deafly grounded neutral, organized according to the principle of protective grounding, is the lack of ensuring protection of a person in case of breakdown of insulation on the body of an electrical appliance during a break in the neutral wire, which is and protective. And this is very important point - grounding is a dangerous measure of protection, so it should not be organized at home in any case!

Modern power supply is still aimed more at safety, therefore, it requires the installation of an RCD and a separate protective grounding loop, through which even the smallest leakage currents will go into the ground, while not endangering a person.

Now you know what a solid-grounded neutral is, what its principle of operation is and in which networks it is used. If you have any questions, you can ask them in the comments below the article!

Related materials:

• Separation of the PEN conductor into PE and N
• Why is a zero break in a three-phase network dangerous?
• How to choose an RCD for power and leakage current