RCD for a water heater: how to check why it works, knocks out the power cord when turned on, options for a boiler

Electricity is a versatile energy source that can be used to heat water. This principle is very often applied in modern water heaters. However, water is a universal conductor, therefore, contact with conductive elements with it should be limited.

Basic concepts

Electric water heaters are devices in which current energy is converted into heat and then transferred to water. Conventionally, such devices can be divided into 2 groups:

  • Flowing. Water heats up in them, passing through special systems with warm plates or pipes that instantly give it away heat. Flow type heaters are very powerful.
  • Accumulative. These include a conventional boiler with heating elements, which consistently heats the water inside the tank.

An RCD for a water heater is a special device designed to protect against current leaks.

The principle of its operation can be described as follows:

  • The device is installed directly in front of the heater itself. All the current passes through it, which feeds the mechanism.
  • If there is a current leak inside the heater, then the RCD catches it, after which the entire system is turned off. Its operation is provided using special sensors and switches.

It should be noted that the RCD, according to the principle of operation, resembles an automatic machine, but technically it is not. It picks up even small fluctuations in current that machines are not able to analyze.

Today, such mechanisms do not always provide an optimal level of safety, therefore, the water heater must also be additionally equipped with grounding. RCDs should not be confused with difavtomat, as these are two different designs. The first mechanism is capable of capturing only current leaks, and the second is more universal: the difavtomat also reacts to short circuits, overloads and other similar problems, while “knocking out” electricity.

Reasons for triggering

Technically, protective systems need not be used. However, for water heaters, they are mandatory attributes. This is due to the fact that the structures are made of metal, and the water itself conducts current well. The use of water heaters without protective systems is unacceptable, as it can become a threat to human life.

The RCD turns off for several main reasons:

  • Damage to the heating element insulation. It is she who protects the entire system from the passage of current. Any user can easily wash their hands without fear of electric shock. However, in old or low-quality water heaters, this element may be damaged. Such phenomena can be checked only with the help of special devices.
  • Leakage current. Very often the RCD knocks out if the cable inside the boiler or the power cord itself is damaged. It should be noted that this can happen in almost any wire. Very often, the cable is directly damaged from the inside, after which the current is supplied to the metal case. To find the cause, very often it is required to disassemble the heater and analyze the situation.
  • The shutdown mechanism does not work. This very often happens with cheap products from unknown companies. They may simply not turn on after several operations.
  • Incorrect location of the RCD. If the device is connected in the wrong place, then it will analyze the wrong currents. In the event of a heater breakdown, the system will not protect a person from current leakage.

How to choose?

RCDs are versatile mechanisms that can be used to turn on and off various household appliances. You can choose such a mechanism for an electric water heater, focusing on some simple rules, which will be discussed below:

  • The power of the RCD is selected on the basis of a similar indicator of the household appliance that is planned to be used. For boilers with a capacity of no more than 2.3 kW, experts recommend installing mechanisms designed for 10 A. If this indicator varies in the range of 5.5-8 kW, you should buy an RCD for 32-40 A. That is why it is so important to pay attention not only on the switch itself, but also on the connected device.
  • Leakage current. This characteristic is calculated based on the operating current indicators. Often 0.4 mA is taken into account per 1 A. If the RCD is installed at a remote distance, it is advisable to add another 10 μA for each meter of cable. It is easy to minimize this value if you install the device directly in front of the water heater itself.
  • Installation method. There are several options for protective devices on the market. The most common are RCDs that can be mounted on a DIN rail. An alternative option is separate blocks that allow you to connect them directly to the outlet.

It should be noted that many modern manufacturers of water heaters build such devices into their appliances.

Elements can be located in an inconspicuous place - under the body or inside the network cable, so it is advisable to clarify this feature before buying a boiler. The advantage of this system is that the manufacturer accurately calculates all the characteristics of the RCD for a heater of a certain power.


RCDs are not complex, but they can be classified according to several criteria. Devices are divided into the following types (depending on the type of leakage current):

  • Class A. They are used for alternating or pulsating electric currents.
  • AC class. These devices are designed for AC operation only. They are one of the cheapest and simplest models used in many apartments.
  • Class B. General purpose industrial devices. They can be used not only for alternating current, but also for direct or rectified current.
  • Sometimes manufacturers add the letter S to the product labeling , which indicates that the device turns off only after a certain period of time. In everyday life, there is no need to use such systems together with water heaters, so they are very rare here.
  • Class G. These RCDs are similar to S, but their holding time is much shorter.

Depending on the method of breaking the circuit, the RCD can be divided into the following groups:

  • Electronic. They are relatively inexpensive devices that are used in simple systems. Experts do not recommend installing them, as they are powered from the electrical network. If the user accidentally damages the neutral wire, the device will simply fail. Another disadvantage is the relatively long response time.
  • Electromechanical. Switches of this type are not powered from external electrical sources, so they are more reliable and of better quality. The only drawback of such devices can be considered only their overpriced.


You can get reliable protection against leaks using an RCD. However, this requires the device to be properly connected to the main network. When carrying out such operations, you should adhere to a few simple rules:

  • The RCD should be connected directly in front of the boiler itself. A separate line machine is installed in front of it, and then a counter and a common input machine for the whole house. If the electric line is used only for a specific water heater, then it is allowed to change the order of the RCD and the machine. However, it is advisable to stick to the first scheme.
  • It is undesirable to place a few additional outlets between the switch and the boiler or connect other household appliances. Experts recommend using separate lines for heaters. The RCD here should only control the boiler.
  • Be sure to supplement the house with a general RCD that will control the entire network. In the event of a device malfunction, the system will be shut down by another device.

Technically, connecting an RCD is not difficult. There are input and output terminals on the case of each device. Neutral and phase wires are connected to them (using special clamps). At the outlet, wires are also used, which already go directly to the boiler or other heater.

One of the errors is the use of only one machine or RCD. It should be understood that these devices complement each other, as they are responsible for different threats. They must be used in pairs.

An RCD for a water heater ensures an optimal level of safety for its operation. If it is necessary to obtain a high-quality and reliable system, then the design of electrical circuits and the installation of all protective devices should be trusted only by professionals.

You will learn even more useful information about RCDs for a water heater in the next video.