RCD connection without grounding: from theory to practice, electrician's advice

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RCD connection without grounding

There is a bias that requires a three-wire electrical network to operate the RCD correctly, i.e.phase, zero and ground. Note, however, that the role of RCD - to disconnect the electrical equipment in the event of a leakage current to the housing, and, therefore, to prevent a person from being electrocuted.

The circuit of connection RCD.Single-phase network.

RCD connection diagram. Single-phase network - Photo 1

The purpose of the earthing is the same: in the event of an electric current on the non-conductive grounded parts of the equipment, create a short-circuit mode from which the maximum current protection of the circuit breaker will operate and the equipment will be de-energized. It turns out that one and the same goal can be achieved by applying two different methods:

  • Connecting the RCD without ground, the circuit of which will be discussed further, or
  • Protective grounding.

These two protection methods can complement each other, but can be used separately. How is the RCD connected in a single-phase circuit? This will be discussed later.

Can I install an RCD in the network without ground?

From all of the above, it can be concluded that the installation of an RCD can be carried out even in a two-wire electrical circuit in which there is no regular grounding. This conclusion is confirmed by the design of this protective device, in which there are phase and zero terminals, but there is no terminal for connecting the ground conductor. This is important, because the grounding conductor is used only in new buildings.

Block diagram of electrical wiring in the room

Block diagram of electrical wiring in the room - Photo 2

In homes built in the Soviet Union, a two-wire system is used, without a grounding conductor. Especially in this case, it is necessary to install an RCD in the apartment. The difference between the operation of an RCD in a network with a ground conductor and a RCD without grounding is only at the moment of operation.

In a circuit with grounding, the device will operate immediately when a leakage current appears, and the RCD circuit without grounding will ensure the protection is activated only when it touches the body of an electrical appliance that is accidentally energized. However, in both cases the RCD provides reliable protection against electric shock due to instantaneous operation.

Principle of operation of RCD( what is RCD)

In order to understand the features of connection of RCDs in a private house or apartment, it is necessary to consider its operating principle. It is based on a simple physical law, which states: the current in the circuit with the consecutive connection of consumers, regardless of their power, does not change in all sections of this circuit.

In other words, the current that passes through the phase and neutral conductors of the same branch of the circuit remains the same. A phase and zero conductor is connected to the RCD, and this apparatus compares the value of the current passing through each of these conductors. If the current is the same - the electrical circuit is operating in normal mode. If the current strength is different, it means that a leakage current has appeared, then the RCD instantly triggers and disconnects the emergency section from the circuit.

The scheme of connection of the RCD for the example of an apartment flap

Connection diagram of the RCD for the example of a housing flap - Photo 3

This is a theory. Now consider its application in a practical example. Let's assume that a circuit is connected to the switchboard, which supplies the electric water heater in the bathroom. From the protection devices in this circuit, only a circuit-breaker is installed, which protects the circuit from overcurrent and short-circuit currents.

Suppose that an insulation fault has occurred inside the heater and the conductor is touching the metal casing. If there is no ground, the circuit breaker will not react in any way to this emergency operation. But this is dangerous, because the case is under tension and if you touch it, you can be hit by an electric shock.

The situation will change, established by the RCD in a private house, apartment or office. After all, the current flowing to the body of the water heater is a leakage current, when it appears, in case of touching the housing, the RCD trips, de-energizing the emergency controlled area. If the circuit includes an RCD without grounding, the circuit becomes much safer from the standpoint of the possibility of electric shock.

How to connect an RCD without grounding

Let's move on to the most important issue of our article: what is the circuit of the RCD without grounding?

As for the very connection of the RCD, it can be produced in two ways.

The first connection scheme for single-phase RCD is to install a single high-power protection device for all electrical equipment in the house or apartment. This method has the advantage of being the simplest. After the electricity meter, the phase conductor goes to the incoming terminals of the RCD, then the conductor goes to the circuit breakers from the output terminals. From the machines, the wire goes to the electrical equipment: sockets and lighting.

This circuit does not take up much space in the switchboard. The disadvantage of this method of installing the RCD is that all electrical equipment of the house or apartment is disconnected when it is triggered. It is also difficult to quickly determine the reason for the shutdown.

The second way to connect an RCD without grounding is to install a separate unit for each hazardous area. In this case, the protection device will cost more, and in the switchboard will take up more space. On the other hand, if one section of the chain is disconnected, the others will remain connected to electricity, and will not have to face the situation when the whole house is de-energized. In this case, the connection scheme for single-phase RCD is as follows: from the meter, the phase wire is connected to each circuit-breaker, and from it to each RCD.

When connecting the RCD to the network, the following rule should be adhered to: you can not combine the null conductors into a node after the RCD.This will result in false positives. In addition, after installing the protective circuit, you should check that the RCD circuit is correctly assembled without grounding. This can be done as follows: connect the electrical equipment to an outlet that is in the circuit of the RCD.If after switching on the device the RCD does not turn off - the circuit is connected correctly. Also it is necessary to check the RCD for triggering as a result of a leakage current, by pressing the "TEST" button on the RCD itself.

Errors that should not be tolerated by

It is very important to avoid the following errors. Some in order to increase the safety of the circuit, connect the grounding conductors of the sockets to the zero conductor or to the self-made ground. This is dangerous, because only a working, properly executed, grounding can ensure human security. Homemade circuits can cause electric shock. For the same reason, it is not possible to connect the grounding conductors of the sockets to the water main and other current-carrying engineering structures of the structure.

It is strictly not recommended to connect a neutral wire to ground, in order to purport to improve the reliability of the system. And the last: with a non-working grounding it is recommended to disconnect and isolate the grounding conductor coming into the electrical shield from the electrical appliances. If this is not done, then in an emergency situation, all the housings of the devices will be under life-threatening strain.

It is best to install the grounding, as well as the installation of an RCD in an apartment or a private house, to qualified specialists. Remember that life and health of people can depend on the quality of the electrical network installation.

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