The use of DR in electrical installations avoids serious consequences due to electric shock, but unfortunately due to the lack of knowledge and doubts of electricians, it is not very common to see the use of DR in installations. The main factor that aggravates the lack of DR in the facilities is the mistrust of DR performance. In this article, we will show in practice the performance of the DR when identifying a current leak.
What is DR?
The residual differential (DR) which is also known as the residual differential switch (IDR) is a mandatory protection device in all electrical installations according to NBR 5410.
The DR is a protection device used in electrical installations and basically works as an automatic switch, allowing the electrical circuit to be de-energized whenever there is a current leakage higher than the minimum current value that the DR is able to detect.
The main objective of the DR is to protect users from electric shocks, as the DR disarms immediately after detecting a certain leakage of electric current going to the individual’s body because in this way the DR significantly minimizes the serious consequences of electric shocks. By identifying this leakage of electrical current, the device also contributes to preventing current leakage in the installations, such as a broken neutral.
What is Electric Shock?
Electric shock is a disturbance of different nature and effects that is felt by the human body, when an electric current circulates through the body. The consequences and changes caused by electric shock in the human body depend mainly on the duration and intensity of the electric shock.
The damage and sequelae caused by electric shock are directly related to the intensity of the electric current and not necessarily to the electric voltage. So the greater the intensity of the current that travels through the body, the greater the effects. Another factor that determines the severity of the electric shock is the path taken by the electrical current in the human body, the path in which the electrical current passes through the heart is more serious.
DR performance in practice!
To put an end to the doubts that many people have about DR, we decided to build a model to show the performance of DR in practice. For this model we use the lamp head to simulate a person suffering electric shock when the person touches a circuit without DR and a circuit with DR. The lamp head is a doll that when there is electric current passing through its body, the lamp in its head lights up, thus indicating that there was an electric shock.
In the image below we have the model that represents a circuit where the phase is protected only by the circuit breaker. The completely bare copper conductor is our ground and the black cable with the bare end is the phase cable.
Now we are going to position the lamp head on the grounding point, and then we place his hand on the phase cable. When the lamp head touches the phase cable we can see which lamp in its head lights up, this is because the lamp head is being electrocuted.
The lamp came on because there is a potential difference between the phase cable and the earth cable. This circuit was enough to circulate an electric current that lights a lamp.
In this situation the lamp head is like a barefoot person stepping on the floor and touching an energized point, causing a potential difference. Under these conditions, a current will circulate through this person’s body, that is, it is an electric shock.
Now we are going to do the same test, but with a DR protecting the circuit and we will see what happens when we repeat the simulation again. We are going to position the lamp head on the grounding point and place its hand on the phase cable, just as we did in the previous test.
Instantly the DR disarms, but that does not mean that the electric shock did not happen, as the electric current circulated through the lamp head body, but as the protection system acted quickly, the lamp did not even go up.
The DR disarms, because when identifying an electrical current leak, which in this example is the current passing through the lamp head and going to the ground, the DR disarms, thus shutting down the circuit as soon as possible, preventing the person from receiving a shock greater intensity and has serious consequences.
A good professional should always cherish the safety of people and their customers so it is important to use DR in electrical installations. Below is a video from the World of Electrical with a complete DR, IDR and DDR class.