Why the RCD knocks out: reasons for triggering and troubleshooting methods

Protection against current leakage is one of the most important tasks when installing electrical wiring. For this purpose, an RCD is installed.The compact device performs several functions and, most importantly, prevents electric shock to a person.

If everything is in order with the device, it turns off the power supply only in emergency situations. But sometimes the device works too often. Let's figure out why the RCD knocks out and how to solve the problem.

Operating principle of the residual current device

The RCD is designed to automatically disconnect an electrical circuit if the differential current in the protected area exceeds the permissible values.

Uncomplicated and operating principle of the device. Phase and zero are connected to the terminals, and the device compares the conductors by current strength.

The device detects current leakage and reacts to it. Due to the features of its purpose and operation, it is also called a residual current switch (RCB)

Theoretically there should be no difference, but in practice there are errors. If this difference exceeds the permissible values, an automatic shutdown mechanism is triggered.

To avoid false positives, it is important to initially select the right device.

The reasons why an RCD trips can be very different - from a real leak to a false alarm. A high-quality and correctly connected device works without failures. Therefore, as soon as it turns off, you should immediately diagnose and eliminate the source of the problem.

What can an RCD react to?

Before troubleshooting, you need to have a good understanding of why an RCD might trip in the first place. This will help you understand the diagnostic features and correctly identify faults, if any.

Safety devices must function without interruption and are therefore tested before and immediately after installation, and also in cases where there is doubt about the functionality

The devices are triggered for the following reasons:

1. Leakage current. The device is bought specifically to detect it, so it simply has to work. If the device has not been knocked out before, you should check the wiring.The insulation dries out over time, leading to leaks. If the cables have been laid recently, then it is possible that there may be defects at their connections or mechanical damage to the insulation when driving nails.
2. Problems with electrical appliance cables. Several devices can be connected to the RCD. If the cord of at least one of them is damaged, this may cause the protective device to trip. Problems also arise if the internal parts of the devices are faulty: heating elements or motor windings.
3. Touching a bare wire. The purpose of the device is to protect users from electric shock. If it triggered when a person touched an uninsulated section of the cable, everything is fine. The RCD performs its functions perfectly.
4. Inappropriate RCD. There are no trifles when choosing a device. If you make a mistake in calculating the technical parameters, the device will trigger falsely and create a lot of problems. Therefore, before purchasing, it would be a good idea to consult with an experienced electrician, clarify the required characteristics, or read our article on how to properly select RCD.
5. Device connection is incorrect. If errors were made during installation of the device, cases of false alarms cannot be ruled out. This also happens when the location of the RCD in the electrical circuit is chosen incorrectly. Therefore, you should strictly adhere to connection instructions.
6. Device failure. The trigger mechanism may simply break. Then the device will vibrate. Also, sometimes the “Test” button gets stuck or other troubles occur. Even the most reliable equipment needs maintenance and repair.

Problems are possible due to an incorrectly designed system.One of the most common mistakes made by electricians is connecting the ground to the neutral conductor. This is absolutely impossible to do.

The rule is known even to novice electricians, but it is violated not only by self-taught electricians, but also by professionals with extensive experience. They do not adhere to the PUE not out of laziness or a desire to harm, but out of the best intentions.

Electrical safety rules are literally written in blood. Violations can cost the life of the installer himself or those who will use electrical appliances. There are diagrams and rules for arranging grounding. They should be strictly adhered to

“Malicious violators” justify their actions by saying that this way they can more reliably protect the user from electric shock.

In theory, it is possible, but in practice, shorting the ground and neutral only increases risks, provokes the operation of automatic protection devices, and creates unnecessary problems.

The main function of an RCD is to protect people from electric shocks. If the device meets its specifications and is installed correctly in the electrical circuit, it will do the job perfectly.

The location of the RCD directly affects its functionality. If the device is installed outdoors, it may be triggered due to adverse weather conditions.

Problems due to outdoor installation

During the rainy season, dampness persists for a long time. The air contains droplets of moisture. If the device is located outdoors, they get inside the housing and provoke current leaks, due to which the RCD mechanism is triggered.

Problems due to moisture can arise not only with those RCDs that are installed on the street. If the house has poor ventilation and insufficient heating, appliances may become damp

The external location of protective devices is undesirable not only because of precipitation. Sometimes devices are triggered by lightning, which increases current leakage. But frosts, on the contrary, reduce the sensitivity of the RCD, because At sub-zero temperatures, microcircuits suffer.

Temporary difficulties during repairs

High humidity can disrupt the operation of the RCD not only in outdoor conditions.

After laying hidden electrical wiring, builders seal the grooves with wet plaster or putty mortar. Until it dries completely, the cables are continuously exposed to a damp environment. If during this period you check the functionality of the protective devices, some difficulties may arise.

You should not check the protective devices immediately after laying the solution into the routes. You need to wait until the moisture has completely evaporated. Dry putty does not conduct electricity, does not cause leaks, and the mechanism should not be knocked out

There are microscopic holes in the wiring insulation. Through them, tiny particles of water seep into the current-carrying elements. Wet plaster mixtures are excellent conductors of electricity. All this can provoke current leaks, to which the RCD reacts.

Diagnostics of functionality and troubleshooting

Solving the problem is possible only after adequate diagnosis. It is necessary to check the correctness of the connection diagram of the protective device. This work should be done especially carefully, because... Installation errors most often provoke false triggering of the mechanism.

Often the RCD trips even after all electrical appliances have been disconnected from the network. This indicates an initially wrong choice. If a 32 A device is installed, it is better to replace it with a 64 A model

Only an experienced specialist can find a breakdown without testing the entire system.

It is much easier to check it step by step:

• The power supply to the entire room must be turned off. The central switch is located in the panel. If the problem occurs in the apartment, then the switch is located in the switchboard on the staircase. After this, the RCD is turned on. Normally the machine should reset it. If not, the device mechanism is broken and will have to be replaced.
• It's worth checking the "Test" button. The central switch must remain turned off. The wires are disconnected from the output terminals of the machine and the switch is turned on. An indicator of normal operation of the button is the “On” position of the device. If the flag is reset without load, then the device is faulty.
• Next, you need to determine how well the device matches the current consumption. First of all, all consumer devices are turned off, and the machine lever is turned on. After this, you need to turn on the equipment one by one.
• One of the devices may knock out the RCD. If this happens, you will need to repair it or buy a protective device designed for high permissible currents.

You can read about other ways to check RCD functionality in this material.

If the RCD trips when electrical appliances are turned off, then the problem is in the wiring. You will have to test it to determine the damaged area.

How to troubleshoot problems yourself?

The easiest way to find a fault is in the internal structure of electrical appliances. By disconnecting them and then connecting them one by one, you can accurately determine which equipment causes the automatic protection to operate. After this, all that remains is to check the device itself.It is possible that it is in perfect order, but it is necessary to install an RCD designed for high currents.

Leakage may be due to malfunctions of powerful electrical appliances or wiring. If the RCD is knocked out due to technology, it is easy to determine

Most often, problems with RCDs arise from devices that have powerful heating elements installed: electric ovens, water heaters, washing machines.

When the “culprit” is found, it makes sense to take it to a service center. Professional technicians will be able to accurately identify and correct the breakdown.

Old electrical wiring can cause a lot of trouble. Ideally, it should be replaced immediately with a new one. But in reality this cannot always be done quickly

An RCD can trip even with new electrical wiring. The reason could be any: moisture getting into an open section of the cable or disconnection of the neutral conductor. To accurately determine the location of the leak, you will have to conduct a complete inspection of the electrical points.

First of all, check the operation of the light sources. This is the easiest way. You need to pay attention to whether the device knocks out when you turn on one of the lamps. If everything is in order with them, the electrical cable route is inspected. It is easier to do this in wooden houses where an open system is installed. But with hidden wiring there are more problems, because... You will need to find a special device and learn how to use it.

To avoid problems in the form of faulty wiring in the future, we recommend reading the article about which electrical cable to use for wiring in the apartment. More details - go to link.

The exact locations of the cables can only be determined using special instruments.Some craftsmen are able to independently make devices that respond to conductors located under a 10-centimeter layer of plaster

Professional electricians often use the Woodpecker detector (E-121). This is an almost flawless device that can accurately determine not only cables in the wall, but also break locations. The operating depth of the alarm is 7 cm. Thanks to it, damaged wiring can be found even under drywall.

A worthy analogue of the “Woodpecker” is the MS signaling device (China). Problems sometimes arise with its use, because... you need to get used to the peculiarities of functioning. MS detects any metal in the walls, so it is triggered not only by wiring, but also by nails. But he “does not see” cables shielded with foil coatings, which creates a number of inconveniences.

To search for wiring and break locations, use models GVD-504A, VP-440, Bosch DMF, GVT-92, POSP-1. You can use thermal imagers, which have also proven themselves to be excellent.

A thermal imager is the ideal tool for an electrician. With its help, you can determine the location of the wiring, find out its quality, and find a break. The only caveat: such diagnostics will be expensive if you buy the device

There are other ways to find hidden wiring. Its approximate location is obvious: the cables are laid strictly vertically or horizontally, so it is enough to imagine the straight lines from the electrical points to understand the diagram. You can pass a switched-on radio or microphone over these places: a characteristic noise of interference appears.

Read more about the rules for wiring and designing electrical wiring in the house Further.

When the location of the leak has been determined, you should find out the nature of the breakdown and fix it yourself or with the help of a specialist.

Conclusions and useful video on the topic

Difficulties often arise with protective devices, but it is impossible to do without them. To prevent problems, you should carefully consider the selection, installation and operation of the RCD. If the device knocks out, use the expert advice given in the videos below.

Video tutorial on choosing an RCD:

Common installation errors:

Reasons why the protective device is knocked out:

To ensure normal operation of the residual current device, it is not necessary to be a professional electrician, but basic skills are required. If you are confident in your abilities, carry out independent diagnostics of the device and correct the problems.

If not, then don't risk your life to save money. Calling a specialist and paying for his work is more profitable than getting an electric shock and not achieving results.

Perhaps you know other reasons why the RCD trips and you know how to deal with them? Please share your experience with other site visitors - leave comments and ask questions in the block below.