Installation of a boiler operating on electricity must be performed using protective disconnecting power. The presence of such devices allows you to avoid human shock and ignition of the wiring.
But there are quite a few RCD models for a water heater with different characteristics. It is necessary to choose the device of protection competently, without confusing it with other automatic machines and switches.
We will show you how UZO works, what are the differences between the protective device and the difacfomat, explain and also explain which parameters must be taken into account when choosing a differential switch. In addition, we have prepared a detailed diagram of the connection of the RCD to the boiler and identified the likely installation errors.
The content of the article:
- Why does a water heater need a RCD?
- Difference of the device of protective shutdown
- Types of differential switches
- How to choose a security device
- Connection diagrams for electric boilers
- Possible installation errors
- Conclusions and useful video on the topic
Why does a water heater need a RCD?
An electric boiler combines water and electricity, and at the slightest malfunction in the hot water heaters, this is a direct path to fire and electrical injuries. The safety of the water heater should be given special attention.
With proper operation, this appliance completely fulfills its service life, but if errors are made during its installation, problems may arise that lead to repairs.
A person is affected not by electrical voltage, but by current - and the higher it is in amperes, the more damage is caused to the human body, which is in contact with a broken water heater (+)
The main purpose UZO - break of the power supply circuit of the electrical installation (its protective disconnection from the network) in case of leakage current. On the one hand, this protective switch prevents the person from being electrocuted, and on the other hand, it prevents the wires from overheating.
If the heating element or the cable coming to it is suddenly damaged, the condensate outside and the water inside the boiler turn into natural conductive element, and when in contact with them or the body of the water heater man beats leakage.
As a result, unpleasant sensations, arrhythmia of the heart and possible death. It all depends on the strength of the impacting current in amperes.
UZO breaks the circuit in case of breakage of the neutral protective wire, reduction of the insulation level and a small value of the circuit current - moreover, unlike other protective automata, the operation occurs much faster (within several milliseconds)
When a leakage current appears in the circuit of a powerful current, they begin to operate in exorbitant modes. But the cross section lived simply not designed for such loads. As a result, the wire starts to heat up very much, burning the insulation. And this inevitably leads to an increased risk of fire in the house.
Thus, without a RCD, it is not recommended to connect the water heater to the mains.
Most common RCD trip situations are:
- damage to the wire and the closure of the exposed wires on the boiler body;
- damage to the insulation layer in the tubular electric heating element;
- incorrect selection of the parameters of the protective device;
- Incorrect connection of the water heater to the power supply;
- malfunction of the leakage current device itself.
In all these cases, in the absence of the RCD, the contact of a person with the body of the water heater or the water heated in it is fraught with serious injury.
Difference of the device of protective shutdown
It is necessary to clearly separate the RCD (differential switch) and difavtomat (differential machine, automatic switch of differential current, AVDT). They have several different purposes, they work in fundamentally different ways and their internal structure also differs.
RCD reacts exclusively to leakage current. A difactomat is a more complex apparatus, of which the protective shutdown device is a part. The differential automaton works not only from the current leakages described above, but also during short circuits and overloads in the electrical network.
In addition to RCD, an additional thermal and electromagnetic trip is present, reacting to those very high currents and short circuits.
Despite the great potential of the difavtomat, you do not need to install it in a circuit with a water heater, the electrical panel already has an ordinary circuit breaker, which, together with the RCD, will perform the same functions. Duplicate protective devices is not recommended.
The main node of the RCD is a differential transformer with three windings (supply, outlet and control). The electric current passing through the protective device excites magnetic fluxes on them with opposite poles. In the absence of leaks, when the water heater is healthy, the sum of the currents is zero.
But in case of breakdowns of the heating element or breakdown of insulation, if a person takes up the bare wire (or a metal case boiler), then through its body the electric current will begin to flow into the ground - as a result, the sum of the currents from zero will become positive.
Then the balance in the transformer is disturbed and the EMF acting on the internal relay instantly opens the circuit, the RCD triggers.
Additional information on the differences between RCD and diphavtomat, as well as the choice of switching device disconnecting load is set out in this article.
Types of differential switches
Installed with water heaters and other electrical appliances UZO are divided by the nature of the leakage current, current to the worker, the number of phases, as well as the presence / absence of delay and the response technology of the device protection.
If the water heater is powerful and three-phase, then a safety device for it should be selected also designed for three phases (with four poles-terminals), for a conventional single-phase device there are only one input and output (+)
All models of the RCD by the type of leakage current are divided into three types:
- "BUT" - designed to operate from an alternating and pulsating current;
- "AU" - low-cost household appliances, triggered by AC only;
- "AT" - industrial options, designed to work in networks with alternating, direct and rectified electric current.
If the RCD marking on the body is present "S", then it is a device with an exposed selective response delay. He breaks the chain only after a strictly fixed time, and not immediately. Such devices are used in cascade protection systems with multiple circuits. In everyday life, they are almost never used.
By the principle of breaking the circuit, the RCDs are:
Electromechanical models do not need a separate external power supply and are more reliable. However, they are more expensive than the latter. But, despite the high price, it is recommended to install electromechanical devices.
Electronic analogues when power surges decrease the efficiency of the device - in such situations, their response time increases. Plus, in the event of accidental damage to the zero conductor, a similar RCD will simply cease to operate without power.
How to choose a security device
The operating current of the RCD determines the maximum permissible load in the circuit that will pass through it. It must correspond to the capacity of the water heater.
For example, if a boiler consumes up to 2.3 kW, then the safety device should be rated at 10 A. For heaters of 5.5–7 kW, a 32 A device is needed. But for boilers of 7–8 kW, an RCD of 40 A is required.
The two main parameters of the protective shutdown device are the rated current “working” (in amperes, “A”) and “leakage” (in milliamperes, “mA”). In household models, they are directly related, but there are special devices that do not have this correlation
The leakage current is indicated in mA (milliamperes). According to the electrical rules, it should be calculated on the basis of 0.4 mA for each Ampere of the working electric current. Plus, another 10 µA per meter of wire to the water heater is added.
It is not for nothing that RCDs are recommended to be installed directly next to the boiler in order to exclude in the calculations the influence of the second parameter.
Considered a protective device in shape and size can be mounted on a DIN-rail in a shield and in the form of a unit with a plug into an ordinary outlet.
There are models of water heaters on sale, which initially come with RCDs built into the cable. All parameters of such protective devices are already pre-calculated for a specific boiler, they only need to be plugged into an outlet.
If the skills of installing electrical wires are not, then you can use the RCD in the form of an adapter in the socket - with connection of the water heater will not be exactly the problem, you only need to choose the parameters of the protective block
One more thing RCD selection - This is the presence of almost every electric appliance natural leakage current. If they are, they are indicated in the technical passport of the water heater.
The rated parameters of the protection device must be at least three times higher than these passport data, otherwise false alarms will constantly occur.
Among the best manufacturers of differential switches are:
- swedish swiss ABB;
- french Legrand and Schneider electric;
- German Siemens and AEG;
- Russian KEAZ, Iek and DEKraft.
European manufacturers have slightly higher prices. At the same time, the products of Russian companies are often not inferior to them in quality.
Connection diagrams for electric boilers
For a water heater, a leakage protection device can be installed directly in the apartment (cottage) switchboard or directly on the wall near the heater.
The principle of the connection sequence in both cases is the same - a boiler, a RCD, a circuit breaker, a meter, and a general circuit breaker. At the same time, the RCD and the automat of a specific line with a socket for a water heater can be swapped, both schemes are correct.
The classic version of the connection of the RCD for the boiler is to install it on the line dedicated to the heating boiler after the machine (+)
Household water heater should be connected to a separate branch from the electrical panel. And ideally, it should not be sockets and other electrical appliances.
The boiler is rather dangerous device. Best of all, if the protective device will work only on him. This will increase the safety of operation of the heater, and simplify the identification of problem areas throughout the wiring around the house.
If the RCD is installed next to the water heater, then the wire from the protective device to the machine in the panel will be without "supervision". If the insulation on it is damaged, the boiler protection device simply will not work. It will not even notice the flowing electric current.
However, boilers are often mounted in bathrooms where there is high humidity. It is also good if an additional total RCD for the whole house is installed in the electrical panel, although it will turn off the network. Otherwise, such a breakdown will inevitably lead to a shock of the person who decided to take a shower.
Possible installation errors
Error number 1. In order for the RCD to operate correctly, contacts between “working zero” and “ground” are unacceptable in the protected circuit. For each of these wires must use its own tire. At the same time, the grounding protection device is not present at all in connection with the device. This conductor is not connected to it anywhere.
The power wire from the electrical panel is connected to the upper terminals of the RCD, from the lower line goes to the water heater - on the contrary it is impossible to sum the wires (+)
Error number 2. The operating current of the RCD is selected the same or with a slight excess of the operating current of the machine in the circuit. The only way circuit breaker will be able to protect the protective device from overloads.
Error number 3. Inexperienced electricians often install outlets and RCDs directly under the water heater. So do not strongly recommended.
Leakage from water-heating titanium cannot be completely excluded, and with such a scheme for the placement of sockets and other electrical appliances with bare wires under the potential “waterfall” before the tragedy is not so long away.
Error number 4. It is impossible to connect the water heater only through the RCD or one automatic device. These devices complement, but do not duplicate. They protect the boiler from fundamentally different problem situations in the electrical network.
Error number 5. If the RCD is selected too sensitive (with low leakage current), it will unnecessarily often trigger a blockage of the circuit. The water heater will always turn off. As a result, the water does not normally heat up and the boiler from continuous on / off can fail.
After completion of the wiring is necessary test the operation of the RCD. For this, most water heaters have a “TEST” function that simulates a leakage current. If everything is connected correctly and the protection is working, then the latter will be triggered with the boiler de-energized.
Otherwise, you need to look where and what is not working as expected. In this case, such checks are recommended once a month and thereafter.
Conclusions and useful video on the topic
There are few nuances in the installation of a safety device, but they are there. To make it easier for you to understand these issues and choose the right device itself, we made a selection of relevant video materials. They describe in detail the principles of operation and circuits for connecting a RCD in a network with a water heater.
Connection of protective devices in networks without grounding:
What is RCD, why is it necessary in everyday life (for example, connecting a washing machine):
It is not recommended to connect the water heater to the network without an RCD. Only a leakage current protection device can save users. There is no difficulty in installing such a device, it can be included in the power supply circuit independently, selecting parameters for electric current.
Do you have personal experience of choosing and connecting the RCD to the water heater? Want to share your knowledge or ask questions about a topic? Please leave comments and participate in discussions - the form for reviews is below.