What is grounding and what is it for
Definition of a concept
In short and simple terms, then:
Grounding is a device that protects a person from electric shock if all electrical equipment is connected to earth. In an emergency, a dangerous voltage "flows" to the ground.
Protection is the main purpose of grounding. It consists in connecting an additional, third grounding conductor to the wiring, which is connected to a device such as an earthing switch. He, in turn, has good contact with the ground.
Grounding is working and protective as intended. A worker is needed for the normal functioning of the electrical installation, a protective one is needed to ensure electrical safety (to prevent electric shock).
Usually grounding (grounding) looks like three electric rods driven into the ground, at the same distance from each other, located in the corners of an equilateral triangle. These rods are interconnected by a metal strip. You could see such rods near houses and structures.
You may also notice that on the walls of many buildings, inside or outside, metal strips are fixed, sometimes painted with yellow and green alternating strips - this ground bus, it is also connected to the ground electrode. A grounding bus is needed so as not to pull a grounding wire from each electrical installation.
The third conductor is usually connected to the body of electrical appliances, providing protection against the appearance of dangerous voltage on it. In cables, it usually has a smaller cross-section than neighboring "working" cores and a different color of insulation - yellow-green.
You can find out what types of grounding are in our separate article: https://my.electricianexp.com/en/osnovnye-tipy-sistem-zazemlenija.html
The requirements for a protective ground loop are as follows:
- All electrical installations must be earthed, including the metal doors of the control cabinets and panels.
- The resistance of the grounding device should not exceed 4 ohms in electrical installations with a grounding neutral.
- Nessesary to use potential equalization systems.
We figured out what grounding is, now let's talk about what it is for.
Why does a person shock
Consider two typical situations when you are shocked:
- The washing machine did its job properly, and when you wanted to turn it off, you felt that its body was “pinching” you. Or even worse, when you touched her, you were seriously “jerked”.
- You decided to take a bath, turned on the water, holding the tap, you felt the same effect of electricity - tingling or a strong blow.
Both this and the other situation are solved by connecting grounding to the housings of devices and all metal parts in the bathroom and installing an RCD or differential circuit breaker for power input to a house or a group of consumers.
How does grounding work
To begin with, we will understand why dangerous voltage appeared on the body of a washing machine or other electrical equipment. Everything is quite simple - the insulation of the conductors for some reason deteriorated or was damaged and the damaged area touches the metal case of some of the equipment parts.
If there is no grounding or grounding of electrical equipment, then when a person touches a damaged device, touch voltage (potential difference on the surface between the points of contact). If you are near damaged equipment, it may step voltage (potential difference between the feet in contact with the ground). Touch voltage and step voltage can be dangerous to humans. To reduce their value to a safe value, protective grounding is used.
For a person, even such small values as 50 mA are dangerous - such a current can lead to ventricular fibrillation and death.
So the principle of grounding is as follows: the body of all electrical appliances is connected to the ground electrode, an additional RCD is installed. In the event of a dangerous voltage on the case, grounding always attracts the dangerous potential to the safe potential of the earth and the voltage "flows" to the ground.
What are RCDs and difattomata used for?
Simple grounding of devices is good, but it’s even better to provide additional protection. To come up with residual current device (RCD) and differential automata.
Difavtomat is a device that combines an RCD and a conventional circuit breaker in its housing, so you save space in the electrical panel.
RCD - only responds to leakage currents. The principle of its operation is this: it compares the amount of current through the phase and through the neutral wire, if part of the current has leaked to the ground, then it instantly reacts, disconnecting the circuit. They are distinguished by sensitivity from 10 to 500 mA. The more sensitive the RCD, the more often it will work, even with minor leaks, but do not install too coarse an RCD for the home.
The principle of operation of a protected circuit in simple language:
When a phase enters the chassis of a grounded electrical equipment, current flows from the phase conductor to the chassis. Then the RCD notices that a current has passed through the phase wire, part of the current must be done somewhere and a smaller current has returned through the zero wire, after which this circuit is de-energized. So you are protected from electric shock.
If you install an RCD in a two-wire circuit without a grounding conductor and the possibility of a current leak appears somewhere, it will work only after you touch this place and the current leaks to the ground through you. In this case, you will also be safe.
We also recommend that you watch the video, which describes in more detail why the grounding of electrical appliances is necessary:
That is all we wanted to tell regarding this issue. Now you know what grounding is, when and how it is installed and what it serves. We hope that the information has been set out for you clearly and easily!