To ensure safety in the house and protect people from electric shock, residual current devices (RCDs) are most often used . They are triggered by current leakage. Buying such devices, people wonder: "How to check the RCD?" just before installation. In this article we will try to answer this question.
What is an RCD?
As we have already said, RCD stands for "residual current device". They, like circuit breakers, are classified as electrical protection devices. But what is the difference? How to check the operation of an RCD?
The fact is that the RCD is triggered by the slightest leakage of current, while the circuit breakers simply ignore small charges. They only respond to overload currents or during short circuits. For example, if a child wants to study the outlet device with a metal object, then it can be shocked by a small discharge. He will go through the body and go into the earth. The circuit breaker will not even respond to such a leakage of current. They begin their action with a leak from 30A.
To provide additional protection for a person from electric shock or from a fire due to damage to the insulation of electrical wiring, household RCDs with a sensitivity of 10 to 300 mA are installed in household electrical networks.
How does it work?
If there are no problems with electricity, the currents in the phase and neutral wires will be equal, but in the opposite direction. This will create magnetic fluxes in the core of the transformer, which will be directed towards each other, and therefore will compensate each other. In this case, the magnetic flux will be zero.
In the case when, for example, a breakdown of insulation occurs, a difference arises in the currents of the wires. A leakage current will appear in the phase conductor, which will be differential for the transformer. That is, the magnetic flux will be different from zero, because different magnetic fluxes will appear in the core.
Then the law of electromagnetic induction enters the work. As a result of this, current will occur in the control winding. If this current reaches a certain value, the electromagnetic relay will trip. It activates the release, and the power contacts of the RCD are open. The final result will be the blackout of the protected UZO electrical elements.
But how to check the health of the RCD? Suddenly it doesn’t work at all? To do this, directly on the device there is a button "Test". It is recommended that you use it from time to time. When this button is pressed, a leakage current is created artificially. If everything is in order with the device and it works properly, then it should work and disconnect the electrical appliances controlled by it.
Tools required to test the RCD
Before you learn how to check an RCD, let's figure out with what tools you can do this at home.
Almost every person can carry out a check using improvised means, and be sure that the protective shutdown device is in good working order. So, to carry out this check, we may need:
- a wire with a plug, in order to apply voltage to the RCD;
- a wire with a cartridge, in order to connect an electric lamp;
- electric lamps of different capacities;
- power tools, such as a knife or screwdriver.
During the RCD test, it is recommended to measure the voltage indicators. Usually it is in the range of 180-240 V. This can be important during the inspection.
What are we checking?
In order to check the RCD at home, as we indicated above, you need a set of simple materials at hand. With their help, we will be able to explore 2 aspects of the operation of RCDs.
To begin with, we will make sure that the purchased RCD is serviceable and can be connected to the network. And also we will evaluate the correctness and speed of the RCD in the event of leaks.
The easiest way to check
To implement this verification method, we do not need the listed tools. We will need only an ordinary battery and a piece of wire. You can immediately take them with you to the store when you are planning to purchase a residual current device.
In qualified stores, you can also request that the RCD be checked by the seller in your presence.
So, how to check the RCD with a battery? Everything is very simple. To do this, you just need to turn on the RCD, that is, put the button in the "On" position, connect the battery between the ground input and the phase output. When the device is working correctly and the battery is charged, the device should work and turn off by itself. You should hear a click, and the button - go to the "Off" position
It may be that the first time you check does not work. Try again by simply turning the battery over.
This method of verification is the simplest, since it can be carried out without connecting an RCD to the electrical network and without leaving the cash register.
We check a single-phase RCD with a sensitivity of 30 mA
Before checking the RCD for operation, it must be assembled. To do this, connect the ends of the wire with a plug to the upper terminals, and the ends of the wire with a cartridge to the lower ones.
To test an RCD with such a sensitivity, a bulb with a power of 20 watts will be enough for us. We screw it into the cartridge and turn on the plug in the socket.
Then turn on the device. To do this, translate the "Off." on the device on If you assembled and connected everything correctly, the light should light up. This procedure is recommended to be repeated 3-4 times. That is, turn on and turn off the device.
Then, leaving the RCD turned on, and the light is on, we press the Test button on the device. If the device works correctly, it should turn off, extinguishing the light bulb. We repeat the procedure 3-4 times, previously turning on the device again.
Now we need to check whether the RCD will shut itself off when a leakage current is generated. Artificially create this leak. We take the free end not fixed in the terminal block from the lamp and disconnect it from the RCD. The lamp turns off, but the device remains on. Then we touch the disconnected wire, for example, the grounded frame from the circular saw. You can also use any other grounded place so that the leak is, but does not harm any appliance, but goes into the ground. Normally, the RCD is turned off.
We check a three-phase RCD with a sensitivity of 300 mA
The main points of how to check the RCD for operability, we described above. Thus, the start of the check will be identical. We assemble the device as described above.
The peculiarity consists only in the fact that the upper terminals are connected by a cable from one network cable, and the second wire is connected to terminal N. The lower terminals are connected as follows: one end of the wire is connected to terminal N, and the other remains free.
Next, we will check each phase pole of the RCD with the same free end of the wire. We plug the plug into the outlet, turn on the RCD and in turn check all phases. If they are all OK, the light will be on.
Also for each phase pole, we check the operability of the "Test" button.
When checking for operation in emergency situations, it is necessary to use bulbs from 40 to 100 watts. An RCD should not work on a 20 W lamp, since the leakage current is not included in the response range of the RCD of such sensitivity. If the device does not work on other lamps, then it is malfunctioning and cannot be used.
So we have learned how to check an RCD before connecting it to the network.
Safety precautions
When conducting RCD checks, we are dealing with electricity. This can be fraught with unpleasant consequences. Therefore, before checking the RCD, you need to familiarize yourself with the precautionary measures and observe them during operation:
1. All operations on connecting and disconnecting the circuits must be done with the voltage off (remove the plug from the outlet).
2. Bare hands should not touch any exposed wires.
3. Protect yourself from electric shock with protective and auxiliary equipment (there should be a dry place for work, it is better to lay a rubber mat or wooden flooring under your feet, work with an insulated installation tool, use rubber gloves if necessary, etc.).
4. If you do not have the slightest idea about electricity, then it is best not to carry out work on the verification and installation of equipment.