Connecting electrical convectors via a contactor

Recommendation points

• Contactor function
• Control method
• Installation site and wiring
• Electrical installation
• Increased system flexibility

Consider the rules and diagrams for connecting electrical convectors and heating devices through contactors. As a rule, this is required for heating control through remote control systems such as CCU or Xital. When used correctly, they make heating operation stable, invisible and very user-friendly..

Contactor function

Heating with electric convectors is characterized by low inertia. To maintain a comfortable temperature, the devices have to work in intermittent mode. With high load and switching frequency, it is impossible to place switching devices in the same housing with thermostats, which are traditionally made in the form of a compact panel. Therefore, this type of heating implies the organization of two networks: load or power, as well as a control one, which controls the operation of the first network..

Compact and modular contactors allow switching fairly high loads – up to 63 A at each pole. At the same time, the current strength in the power supply circuit of the contactor itself is negligible, it rarely turns out to be higher than a few tenths of an ampere. Such a small load is quite within the power of the control circuits of all types of thermostatic devices. Thus, the switching on and off of heating devices is performed in steps, which contributes to an increase in the service life and maintainability of the entire heating system..

Scheme and principle of operation of a three-pole contactor: 1 – fixed power contacts; 2 – movable core with contacts; 3 – load; 4 – electromagnetic coil

It is important to understand that the contactor is able to manage a significant load not only due to more massive live parts and an increased contact area. The mechanism of these devices provides for the possibility of ultra-fast closing and opening of the contact group, plus devices for accelerated extinguishing of the electric arc are located inside the case. It is these differences that allow the contactors to operate several hundred times during the day without experiencing overheating and without the formation of carbon deposits on the contact surfaces. Therefore, the installation of a contactor is strictly recommended even if the switching capacity of the relay group of the thermostat (usually 10 or 16 A) significantly exceeds the consumption currents, for example, when a 500-800 W convector is connected to it..

Control method

Unlike magnetic starters for controlling motors and other types of consumers, the contactor for convectors works on a different principle. In the case of switching electrical heaters, a self-pickup circuit is not required. Thus, the contactor does not have to have additional blocking contacts, their presence only leads to an unjustified increase in the cost of the electrical installation..

Since the power supply to the contactor coil is controlled by an additional device, the assembly scheme is extremely simple. A wire of three or more cores is laid to the installation site of the thermostat. Two of them – phase and zero – supply the thermostat itself. In this case, the phase is also used as a power supply for the midpoint of the relay group. Third and other additional conductors – signal return for connecting one or more contactors.

Wiring diagram for convectors through a contactor: 1 – automatic switches; 2 – cross-module; 3 – contactor; 4 – thermostat; 5 – electric convectors

The location of the thermostat is determined taking into account two circumstances. The first is the requirement for ease of access for control, while the thermostat should not disturb the interior composition. The second aspect is the proximity to the location of the temperature sensor. Typically, a thermosensitive element is placed on the ceiling, with the cut-off temperature selected 3-4 ° C higher than that which must be observed in the habitable area of ​​the room. The response hysteresis is selected within the range of 2-3 ° С, thus, the supply of overheated air in the upper zone provides minimal inertia, which provides the room with residual heat during the downtime of the heating devices.

Looking ahead, we note that such a control scheme is not always the most convenient and therefore is not the only one. The very fact of using contactors allows the use of completely different control systems: remote, timing, as well as combined and even with switching to manual.

Installation site and wiring

Despite the compact dimensions of modular contactors, it is not customary to place them in residential premises. The reason for this is simple: a modular flap, even of a hidden type, violates the appearance of the finish, moreover, during operation, the contactors cannot boast of an absolutely zero noise level. However, the placement of switching devices in habitable rooms is not required, all the same, the power supply of the power lines with electric heating is carried out from the ASU, it is there that it is best to place the control assembly.

Naturally, all convectors in a building do not have to be connected through a single contactor controlled by a single thermostat. As a rule, for each living room, its own circuit is assembled, in which, depending on the number of convectors, either several single-pole contactors or one multi-pole contactor are used. Connecting several lines to one pole of the contactor is highly undesirable, otherwise repair work in one area will require disconnecting the entire group.

The practice of connecting powerful electrical appliances with separate lines fully fits into the specifics of modern electrical installation. Unlike general-purpose socket groups, it is not customary to use junction boxes in the heating network. A separate 3×2.5 mm cable is laid from the control panel to each convector², to which only one heating device is connected.

Depending on the building plan, the layout of the electrical distribution network may differ. For example, if in a large building it is possible to place intermediate shields in an uninhabited area, one main line, protected by separate machines, will follow from the ASU to them. In each panel, an assembly of contactors is installed, connected by a signal wire to the local control device, and then a branched power supply network of consumers is laid with separate lines.

Electrical installation

A typical assembly diagram of an electrical panel begins with an input device, which in this case is optimal for a differential machine. Its output terminals are bridged to the cross-module, from which further wiring is performed. Since contactors are not designed to protect against short-circuit currents, it is better to use double-row shields for optimal layout of electrical devices. In the top row, the required number of circuit breakers is set to protect each line. Directly under each of the machines, a corresponding contactor is installed, to which the phase conductor of the line that it controls is connected is connected. When connecting the convector power cables, the protective and working neutral conductors are not combined at any point in the circuit, they are separated into different blocks of the cross-module.

Connection diagram for electric convectors: 1 – input automatic machine; 2 – counter; 3 – RCD / difavtomat; 4 – cross-module; 5 – automatic switch; 6 – thermostat; 7 – air temperature sensor; 8 – contactor; 9 – electric convector

The situation becomes more complicated when the control devices are also mounted in the modular panel. These can be both programmable thermostats with a remote sensor, and remote control devices (Xital) or logical controllers (CCU). In such cases, the shield should be three-row: in the upper row, an input device is installed together with control and automation devices, the lower two are diverted to accommodate circuit breakers with contactors.

Since the supply lines of the convectors are fixed-type wiring, they should be carried out with a cable with single-wire veins in vinyl insulation. Such conductors do not require crimping to connect to the terminals; it is enough to simply strip them and roll them into a ring. When the number of controlled lines is more than two, it is highly desirable to carry out marking: at the point of cable entry into the shield, a belt tag clings, while the phase conductor is crimped with a corresponding cable mark at the end.

Control wiring, as mentioned, is a cable with three or more conductors. Neutral (blue) is connected to the corresponding block of the cross-module, phase – to the output of the low-current circuit breaker. The remaining cores, according to the marking, are connected to the terminals of the contactor coils, marked with the letter A with index 1 or 2. The second terminal is connected with a jumper to the neutral block of the cross-module.

Note:such a connection is correct only if the supply voltage of the contactor coils is mains, if 24 or 36 V devices are used, the circuit is supplemented with a step-down transformer. In this case, an additional conductor must be provided in the signal cable going to the thermostat, through which the reduced voltage is supplied to the middle point of the contacts of the relay group of the thermostat.

Increased system flexibility

In conclusion, we note that the operation of electric convectors in automatic mode is not always convenient. This happens if one of a group of heating devices connected to one thermostat is located near the workplace and the temperature in this zone significantly exceeds the comfortable one.

The way out of this situation is to install the switch on the panel for manual operation, which can be done even after the complete installation of the electrical network. The bottom line is to embed an ordinary two-position toggle switch with two groups of contacts of the necessarily opposite type of inclusion into the body of the shield. For the same purpose, you can use the double modular push buttons with fixation. The first contact is set in the gap between the coil power supply phase, the second is used to force the power supply and, accordingly, turn on the line on a permanent basis. When operating in manual mode, the convector is controlled either by a built-in temperature controller or by a through-type socket thermostat.

Convector connection via socket thermostat

The exact same principle can be used to transfer the system from remote control to local automation or to switch to timing operation, which is often used in buildings that are not intended for permanent residence. The difference in the circuit design is small: instead of switching the supply phase of the coil of one contactor, there is a counter-switching of the supply phase of the thermostat and the second, alternative source of the control signal. To exclude counter-switching, it is enough not to use one phase wire to connect the contact group and power the device itself.