What is a grounded neutral – simple definition

Device and principle of operation of networks with an earthed neutral

The principle of operation of electrical energy sources, in particular, step-down transformers, is based on the law of mutual induction and energy transfer through a magnetic core. In this case, the primary coil may not have a neutral wire, unlike the secondary wire, connecting it to zero through a low-resistance conductor, which can equate to a zero value, will be an effective way to protect people from voltage damage that threatens their life and health.

The main feature of networks with a grounded neutral is the appearance not only of linearity, but also of phase voltage. What it is and how they differ from each other, let us consider an example of a simple pie chart.

Phase voltage is the voltage between one of the line wires and the zero point connected to ground, i.e. tightly grounded. Line voltage is the potential difference between the two results of the line, i.e. L1 and L2 or L1-L3 or L2-L3, and is also called interphase. These sources of electrical energy in everyday 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, i.e. by 1.72.

But the main task of such a system is not only to transmit voltages of two values ​​​​to consumers with a different number of phases in one power supply system, but also to protect a person during insulation breakdown and the appearance of voltage at points that would not have dangerous potentials in the normal state. In residential buildings:

• Cases of all household appliances that conduct electrical current, i.e. made of steel or other conductive metals;
• Metal structures for keyboards and switches;
• Cable sheath.

Also, to ensure safety, all of the above items must be grounded, in this case the risk from applying voltage and using household appliances in networks with a grounded neutral will be minimal. Moreover, uniformity of single-phase load distribution is mandatory for these circuits.

Explanation for dummies

The step-down substation in which the transformer is installed has its own ground loop. They are connected to steel frames and bars, in a single ground loop. A cable to consumers is laid in the electrical panel of the substation, which has four cores. If the consumer needs power from a three-phase 380 V circuit, it is necessary to connect to all cores. In a single-phase network with a voltage of 220 V, power will be supplied from the neutral wire and from one of the phases.

People should be protected in single-phase and three-phase circuits, if there is no grounding system, which is operated by a small to zero leakage, while reliably disconnecting the consumer from the network.

Classification of networks with neutral grounding

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

• L is the phase conductor;
• N is zero action;
• RE – protective neutral conductor;
• PEN – working and neutral conductor made with a single wire.

There are several subsystems in circuits with a power supply that has a grounded neutral:

• TN-C. With this system, the neutral and protective conductor of the substation are regulated by a single conductor, near the receiver whose case (or other elements to be grounded) is connected to this combined conductor – this is called grounding. This is an old system that was used in old houses under the USSR; Now it is not used for home consumers, because it is unsafe. Such a system has a significant drawback, because if the PEN connector breaks down on the way from the supply transformer to the power receiver, dangerous potentials appear in cases of canceled equipment. It is used only to protect industrial consumers (this will be described later in the next section).
• TN-S. It has a higher rate of safety during emergency situations. This is achieved by disconnecting the protective conductors and running along the entire supply line, from the transformer to the distribution board (to the final consumer). However, due to the fact that it is necessary to use cable products with five cores, which significantly increases the cost of laying and the budget for organizing power supply to the consumer, this system is not always used.
• TN-CS. This grounding system is the most common in our time. With this system, the neutral and protective conductors along the entire line are combined into one compact PEN conductor. Entering the building, this conductor is divided into PE and N zero protection, which are also distributed to consumers (apartments). With this system, if the PEN conductor is burned to the point of disconnection, dangerous potentials will appear on the grounded housings of electrical appliances. To prevent this, repeated grounding of the PEN conductor is performed along the entire line and at the entrance to the building and increased requirements are placed on the mechanical protection of this conductor.
• TT. This grounding system is applied if the TN-CS system line is in unsatisfactory technical condition and the integrity of the protective grounding provided for is not ensured. This grounding system provides for the installation of an individual grounding loop at the consumer, while the PEN conductor of the electrical network is used only as a neutral wire N.

It’s important to know

For single-phase and three-phase power supply to consumers in industry and domestic conditions, the so-called grounding, which is supposed to be an effective method of automatically shutting down an electrical installation or a part of it in which a short circuit has occurred. When grounding in circuits with a grounded neutral, all metal parts and cases of electrical equipment are connected With zero wire. How does this protection work? The fact is that with any short circuit of the case, the circuit goes into short circuit mode, the current in the circuit breaker circuit increases significantly and the emergency section is disconnected from the network.

The advantage of such a system is to save expenses on protective grounding wires, as well as reduce the cost of cable products, since single-phase and three-phase power receivers can be connected to the same circuit.

However, the lack of a grounded neutral, regulated by the principle of protective grounding, can be called a lack of human protection in case of breakdown of the insulation on the device body while cutting the zero wire, which is also protective. And this is a very important point – grounding is a serious measure of protection, so it should not be organized at home!

However, a modern power supply is aimed at greater safety, so it requires the installation of an RCD and a separate protective grounding circuit, through which even the smallest leakage currents will go to the ground, without exposing a person to danger.

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