When wiring an introductory electric switchboard, home masters often do not know the necessary sequence of protective automation elements to connect without the necessary experience. Such knowledge gaps can lead to sad consequences in the process of exploitation. This is especially true for the inclusion of residual current circuit breakers in the circuit. If with AVDT everything is simpler, then the question of where to install the RCD (before or after the machine) requires a detailed review. In today's article, we will consider how to perform such an installation, as well as the sequence of arrangement of the protection elements of the home electrical network.
The principle of operation of RCDs and its difference from a differential automaton
The need to install a residual current device has not been disputed by professional electricians for a long time, but even some of them have errors in its connection. This device serves to protect a person from electric shock in case of leakage as a result of breakdown of insulation or excessive dampness and requires a properly mounted grounding. When connecting an RCD, 2 wires (at 220 V) or 4 (at 380 V) are used. The resulting current leakage creates a potential difference on the coils of the device, which leads to a cutoff.
However, such a device has one significant minus - it is not able to detect network overload or short circuit, which can lead to its failure without removing voltage. That is why the RCD requires additional protection, in contrast to a differential current circuit breaker (AEDT).
The essence of the work of protective elements in the complex
In order to understand where to put the RCD (before or after the machine), a novice home master needs to learn how his work will be done. For example, it is worth taking the simplest assembly, in which there is a metering device, a residual current device, circuit breakers with only one power line output. In this case, the voltage that came from the transformer substation, passing through the meter and RCD, should go to the outlet. However, in the absence of protection and the occurrence of a short circuit, the residual current circuit breaker burns out.
But in front of the counter, a trip is also necessary, which means that installing an RCD after the introductory machine will be the right decision. It turns out that protection is necessary on both sides. However, such a bipolar machine is installed before the meter. Directly in front of the protective shutdown device, it is not necessary to install it, but on the segment from the RCD to the consumer they are necessary. However, such ABs will differ from the introductory ones in various parameters, which should be considered separately.
What machines to put after an RCD
Quite often, beginner home masters have a question, how do the introductory AVs differ from those that are installed after the protective shutdown device. The following criteria can be distinguished here:
- maximum current load (at the input automatic machine it is higher);
- number of poles (2 or 1);
- main purpose.
The introductory machine (with the correct switching of the rest of the protection) is very rarely used for its intended purpose. Most often, the rest of the equipment of the electrical panel works earlier. It is mainly used for general disconnection of the home network during the repair work. Its rated current load is higher than that of the other elements. As input, bipolar ABs are used, through which both phase and neutral wires pass.
The rating of the machines after the RCD is lower. This parameter is calculated depending on the planned load on a particular line. However, it should be understood that it should not exceed the same indicator of the residual current device. The main task of a linear single-pole circuit breaker is to cut off the group when an overload or short circuit occurs on it before the RCD breaks down.
Sample switching scheme using a single residual current device
The location of the automation in the opening electrical panel may vary. Typically, a single residual current device for all outgoing groups is sufficient. But even if several similar elements are used, the question of "putting an RCD before or after the machine" is incorrect - installation on both sides is necessary. It is worth considering in what order the elements will be arranged.
- Introductory bipolar circuit breaker or feeder circuit breaker.
- Electricity metering device.
- Residual Current Device
- One or more machines, depending on the number of lines.
Quite often, home masters are reinsured and install an additional AB between the meter and the RCD, however, if all the calculations are done correctly, this element is completely useless.
Assembly on multiple residual current circuit breakers
A similar option is applicable if you need separate protection for household appliances installed in wet rooms (washing machine, boiler). In this case, an RCD mounted on a separate line should have lower indicators than the main one. Often, additional residual current circuit breakers are installed directly near the protected equipment, outside the distribution cabinet. But here, one should take into account the experience of switching an input shield. The answer to the question of where to put the RCD (before the machine or after) will be the same.
The most rational for such protection of individual equipment would be the acquisition of a compact AVDT. Such devices are plugged into a conventional outlet and can withstand currents up to 16A, which is enough for a dishwasher or washing machine. In addition, they do not require any skills in the field of electrical installation.
Important! Connecting an RCD after the machine without its additional protection is possible, however, it should be understood that in this case the AB rating must be one step higher than the same indicator of the residual current device. In this case, even if a short circuit occurs, nothing extraordinary will happen. The time-current characteristic of the machine (about 0.02 sec.) Will allow to cut off before the RCD will fail. However, such a scheme is applicable for only one group.
Video example of connecting protective equipment
In order for a respected reader to understand more clearly how to connect an RCD (before or after the machine). Below is a short, but quite informative video.
Grounding and its role in the operation of the residual current device
When installing such equipment, you need a circuit that correctly performs its work. Regardless of whether an RCD is installed before or after the machine, without properly installed grounding, it will not be able to provide adequate protection. Of course, it will save you from a fatal outcome, but you will have to experience a sensitive unpleasant discharge. It is worthwhile to understand why this happens.
Everyone knows from the school physics course that current flows along the path of least resistance. When the breakdown of insulation and the contact of the phase wire with the housing of the household appliance, its metal parts are under voltage. If the grounding functions as expected, the current will "flow" just along the path of least resistance, which will create a potential difference in the coils of the residual current device, which will lead to a cutoff.
And what happens in the absence of a normal circuit? In this case, the device will be constantly energized. If a person touches him, then not a fatal, but a very sensitive discharge is provided. In this case, the current will also rush to the earth, but through the body. Of course, the RCD will shut off pretty quickly, but such a blow is also unpleasant.
Connecting residual current circuit breakers: basic rules
When switching an RCD (in front of the machine or after - it does not matter), many make mistakes leading to its incorrect operation. The most common of these is the connection of grounding and zero. Such an action will lead to unreasonable operation when turning on household appliances. The same can be said about the jumpers inside the outlets connecting the ground and ground contacts. Often this happens when the owner moves to a new apartment and installs an RCD, which was not there before. If the device turns off for no reason, the algorithm of actions should be as follows:
- When RCD is turned on, the TEST button is pressed. A cut-off should occur.
- The absence of contact between ground and zero in the control cabinet is checked.
- Sockets in turn are opened. The connection inside must be made correctly, without jumpers.
- If the cause is not found, it is necessary to check the wiring in the junction boxes.
However, it often happens that there is a breakdown and a short to the case. Therefore, before performing the above actions, you must turn off all household appliances from the network, and then turn them on in turn. When an RCD trips on one of them, it is necessary to try at the same point another device equipped with a plug with a grounding contact.
Testing the residual current device
This is one of the most important actions for periodically servicing the equipment of electrical cabinets. Provided that all the wiring in the apartment or private house is done correctly and regardless of whether an RCD is installed before or after the machine, it can be checked in several ways. A common option used by the bulk of electricians is a multimeter, but you should not dwell on it. It is much more interesting to consider two other ways:
- Incandescent lamp - an option for checking the functionality of an RCD in place.
- Finger-type battery - tests upon purchase, without connecting to the network.
It is worth considering both methods in more detail.
Using an incandescent lamp
If the home master is sure that the grounding is functioning correctly, the algorithm of actions is as follows. First you need to determine the phase contact in the outlet. After that, one of the wires connecting to the lamp holder is connected to it. The second wire should touch the ground terminal. If the residual current device is operational, it will trip by disconnecting the voltage.
Very important! If zero is connected to the ground terminal, a short circuit will occur. That is why you should perform such actions if the home master is 100% sure that the wiring is done correctly. Otherwise, it is better to use the second method.
Functional test with a finger battery
This method can be applied upon purchase. If the RCD is already installed, you must turn off the input circuit breaker and dismantle it. To work, you need two pieces of wire and a galvanic cell. The wires are connected to a pair of phase or zero contacts (input / output). A battery is connected to the other ends of the wires, which creates a field on one of the coils. The resulting potential difference forces the residual current device to cut off. If this does not happen, then the RCD is inoperative.
To summarize the above
To install an RCD before or after the machine is up to everyone to decide, depending on the number of groups leaving for the apartment. However, experts advise against additional protection. So, installing the machine after the RCD is more acceptable.