A correctly assembled non-switchable group in the panel after the voltage relay guarantees the safety of expensive household appliances during network surges and at the same time ensuring the operation of critical consumers, such as refrigerator or gas boiler, even when the main circuit breaker is turned off. An error in the connection sequence, when the input circuit breaker breaks the power circuit of the relay itself, will lead to the fact that the voltage protection will cease to function, leaving the equipment without monitoring the network parameters. To create a safe power supply system, it is necessary to strictly adhere to the switching order, where the input switch controls only the load, and the voltage sensor is powered directly from the meter or through a separate maintenance-free circuit breaker.
Many electricians make the fatal mistake of running the phase wire through the input machine before feeding it to voltage control relay (RKN). In such a scheme, when the protection is triggered or the “switch” is scheduled to be turned off, the relay is de-energized and physically cannot supply voltage to the network again after the parameters are normalized, which actually turns the smart device into a simple circuit breaker. The correct configuration requires that power supply of the relay itself and the circuit of the non-switchable group were located before the switching device that controls the main consumers, providing constant monitoring of the network status 24/7.
The implementation of a scheme with a non-switchable group requires the allocation of a separate line for vital consumers, which bypasses the main switch of the apartment or house, but passes through the relay protection. This allows the owner to turn off power to the entire apartment to replace an outlet or go on vacation, while maintaining work security systems, server or freezer with food. Below we will analyze in detail the technical implementation of such a circuit, the necessary components and typical errors that can cost you burnt electronics.
Operating principle and purpose of a non-switchable group
The main task of the organization non-disabled group consists of dividing electricity consumers into two categories: those that can be de-energized with one movement of the input machine lever, and those that must remain energized constantly. The first group includes lighting, sockets for household appliances, air conditioners and heated floors. The second group includes refrigeration equipment, video surveillance systems, server racks, heating boilers and water supply pumps that depend on electricity.
The key element in this chain is voltage relay, which acts as a guard. It continuously measures the incoming voltage and, if the values are outside the specified limits (for example, below 170V or above 260V), it opens its internal contact. It is important to understand that voltage relays do not protect against short circuits or overcurrent - they are used for this purpose. circuit breakers. The function of the relay is to save the electronics from “poor-quality” voltage, and the non-switchable group ensures the continuity of this protection even when the input is disconnected.
The circuit is constructed in such a way that the input circuit breaker (switch) breaks the phase going to the main groups of consumers, but does not affect the line supplying the protection itself and the critical load. This creates the effect of “double protection”: the equipment is protected from relay voltage surges, and the ability to completely turn off the apartment is preserved for safety when servicing the wiring. Without such an organization, owners often face a situation where, after a thunderstorm or accident at a substation, expensive equipment burns out while the owners were away.
- 🔌 Continuous monitoring: The relay controls the network even when the input circuit breaker is turned off, if it is powered correctly.
- ❄️ Product safety: The refrigerator continues to work even if you forget to turn off the lights or go to the country.
- 🔥 Boiler safety: The electronics of a gas boiler will not burn out during a power surge in the absence of the owners.
Selection of equipment for shield assembly
To implement a high-quality circuit with a non-switchable group, it is not enough to simply buy the first relay you come across. The market offers many devices, but for long-lasting performance, you should choose trusted brands such as ABB, Legrand, IEK or specialized brands like ZUBR and Novatek-Electro. It is critical that the rated current of the relay exceeds the total current of the protected group, or it must be paired with contactor (starter) if the load is large.
The input circuit breaker or circuit breaker must be of high quality, since it will bear the main load when turning on/off the entire apartment. For a non-switchable group, a separate machine with the characteristic is often used C, which protects the cable going to the refrigerator and boiler from overloads. Don't skimp on tires N (zero), since incorrect connection of zeros is the most common cause of equipment failure.
When choosing a relay, pay attention to the presence of a switch-on delay function. For compressor refrigerators, the minimum delay should be at least 300 seconds (5 minutes) to allow the freon circuit to stabilize after a power surge. Modern models allow you to configure this parameter through the menu or have fixed factory settings, which eliminates the need to buy a separate time relay.
⚠️ Attention: Never use a voltage relay with a rated current “buttock” to an input circuit breaker. If there is a 40A circuit breaker at the input, the relay must be at least 63A, or the circuit must include a contactor. Operating the relay at its maximum capacity will lead to burning of the contacts and a fire.
Typical connection diagram in a distribution board
Assembling the visor begins with understanding the flow of energy. The input cable from the meter goes to the input circuit breaker (or switch), but to organize a non-switchable group, we make a branch to this circuit breaker. Phase wire L from the meter it goes to the input of the voltage relay, and also through a separate circuit breaker (protection of a non-switchable group) to critical consumers. The relay output (a contact that opens in case of an emergency) supplies a phase to the contactor coil or directly to a group of circuit breakers of the main consumers.
Neutral wire N in most schemes it goes directly from the zero bus to consumers, bypassing the relay (if it is a single-phase relay that breaks only a phase). However, the zero input terminal on the relay itself must be connected, otherwise the device will not work and will not be able to measure voltage. An error in connecting the zero often leads to the relay indicating voltage but not switching the load, or the internal electronics burning out.
To implement a circuit with a contactor (which is recommended for currents above 40A), the phase from the relay output is supplied to the contactor control terminal (usually A1). The power contacts of the contactor (1-2, 3-4) are connected to the phase break of the main groups. Thus, the relay controls only the small coil of the contactor, and powerful currents are switched by the power contacts of the starter. This significantly extends the life of the entire system.
Connection diagram for three-phase network
In a three-phase network (380V), three single-phase relays (one per phase) or one three-phase are used. When using three single-phase relays, each protects its own phase. If one phase "loses" or goes out of bounds, all three relays must disconnect the load. To do this, the relay outputs are connected in series or through a logic block to break the power supply circuit to the coils of three contactors at once.
Step-by-step installation instructions
Installation begins with installing the DIN rail and placing all modular devices: input circuit breaker, voltage relay, group circuit breakers, RCD and contactor. First, connect the zero bus: the incoming zero from the meter and the zeros of the outgoing lines. Then connect the phase from the meter output to the input of the input machine and in parallel (with a comb or twist through a pressed tip) to the phase input of the voltage relay.
Next, we form a control chain. From the output of the voltage relay (a contact that closes when normal), we lead a wire to the terminal A1 contactor. The second end of the coil (A2) set to zero. Now, if the relay sees the norm, it supplies a phase to the coil, the contactor clicks and releases current to the main groups. For a non-switchable group, we transfer the phase from a separate circuit breaker (which is powered up to the input switch) directly to the consumers, bypassing the contactor, but passing through its circuit breaker.
☑️ Assembly verification checklist
After assembly, it is necessary to conduct a visual inspection for protruding wires and the correctness of the circuit. Then, with the input disconnected, we check the insulation resistance (if you have a megohmmeter) or simply recheck the circuit according to the drawing. It is better to carry out the first start without a connected load, simply observing the relay indication and the operation of the contactor when the input circuit breaker is turned on.
Common mistakes when assembling a shield
One of the most serious mistakes is connecting the consumer zero to the bus, and the relay zero to another, unconnected terminal, which leads to phase imbalance or inoperability of the device. In a single-phase network, all zeros must converge to one point. It is also often forgotten protection of the relay itself: in front of the phase input on the relay there should be an automatic circuit breaker (usually 1A-6A), which will protect the insides of the device in the event of an internal short circuit.
The second mistake is ignoring the current load. Installing a 32A relay in a panel where the input circuit breaker is 50A will lead to the fact that when you turn on powerful appliances (washer + kettle), the relay will burn out, even if it is located before the contactor (if you mistakenly power the load directly through it). A voltage relay is an automation device, not a power switch for constant operation under full load.
- 🔥 Overheating of contacts: Poor tightening of screws leads to heating, melting of the housing and fire.
- 🔌 Lack of selectivity: Setting the upper threshold of the relay is higher than the operating voltage of the input circuit breaker (meaningless protection).
- ⚡ Confusion of inputs and outputs: Supplying the network to the relay output is guaranteed to disable the device.
Setting thresholds and testing the system
After installation, it is necessary to adjust the response thresholds. For a 220V household network, the following values are considered optimal: lower threshold 170V - 190V, upper 250V - 260V. A range that is too narrow (for example, 210-230V) will lead to constant false shutdowns, and a range that is too wide will not protect the equipment. The switch-on delay for refrigerators must be set to at least 300 sec, enough for the rest of the equipment 30-60 sec.
It is better to test the system using a laboratory autotransformer (LATR), if possible, or by simulating an accident (carefully!). Check that when the voltage drops below the set minimum, the relay turns off the contactor, and when it returns to normal, it pauses and turns on again. Make sure that the non-switchable group does not turn off if it is wired correctly (bypassing the contactor, but passing through the relay, if the relay is single-phase and is at the input of the entire apartment).
Tip: If you have a three-phase input, do not use one three-phase relay to protect all equipment. If one phase fails, it will turn off the entire house, including the refrigerator. It is better to install three single-phase relays for each phase separately.
It is important to periodically, at least once every six months, check the performance of the system. Visually inspect the shield for dust and heat. If the relay has an event log feature, check to see if there were any power surges while you were away. This will help you replace the device or adjust the settings in time.
| Parameter | Recommended value | Consequences of an error |
|---|---|---|
| Lower threshold (Umin) | 170-190 V | Frequent shutdowns or operation of equipment at low voltage |
| Upper threshold (Umax) | 250-260 V | Risk of equipment burning out or constant blackouts |
| On delay | 300 sec (cold) / 30 sec (other) | Refrigerator compressor failure when turned on again |
| Relay rated current | One step above the introductory machine | Burnout of relay contacts, fire |
Frequently asked questions (FAQ)
Is it possible to do without a contactor and connect the load directly through a relay?
Only if the total load current is significantly less than the relay rating. For example, if the relay is 40A, and you only protect the refrigerator and boiler (up to 5A in total), then you can. But if the whole apartment goes through the relay, a contactor is required, otherwise the relay will burn out.
What to do if the relay clicks constantly?
This means that the voltage in the network “floats” on the border of the threshold values. Try expanding the response range (for example, make it 160-270V) or increasing the restart delay time so that the system stabilizes.
Is it necessary to install a separate circuit breaker for the non-switchable group itself?
Yes, definitely. The cable going to the refrigerator and boiler must be protected from overload and short circuit by its circuit breaker, even if it bypasses the apartment's input switch.
How to understand that the voltage relay has failed?
If there is an indication on the relay, but there is no voltage at the output (with normal input values), or if the relay does not turn off the load during an obvious surge (checked with a voltmeter), the device is faulty and requires replacement.
Main conclusion: A non-switchable group after the voltage relay is not a luxury, but a necessity for modern housing. It provides a balance between safety (the ability to turn off power to the apartment) and comfort (the operation of vital systems). The correct connection diagram prolongs the life of the equipment and the nerves of the owners.