Entrance machine to an apartment: how to choose, connect and avoid mistakes

The input machine is the first and most important element of protecting the electrical wiring in the apartment. Not only the stability of the operation of all electrical appliances, but also the safety of residents depends on its correct selection and installation. Many people mistakenly believe that it is enough to install any machine at 25-32A, but in practice this approach often leads to overheating of the wiring, short circuits or false alarms.

In this article we will look at how to choose input circuit breaker taking into account the cable cross-section, total load and PUE requirements. Let's look at connection diagrams (single-phase and three-phase), typical installation errors and the nuances of coordination with the management company. We’ll also answer the question why ABB S200 or Schneider Electric Acti9 often recommended by professionals - and is it worth overpaying for the brand.

Why do we need an input machine and how does it differ from group machines?

Input machine (aka input circuit breaker) is installed on the border between the external electrical network and the internal wiring of the apartment. Its main tasks:

• 🔌 Short circuit protection - instant shutdown when there is a current surge that can melt the wiring.
• ⚡ Overload Prevention — if the total power of the devices exceeds the permissible limit, the machine will operate before the cable heats up.
• 🔧 Sharing of Responsibility - the border between the service area of the electricity supply organization and your apartment.

The main difference from group machines (which stand on separate lines - sockets, lights, stove) - rated current. The input machine is designed for total load of the apartment, while group ones only protect their own branch. For example, if you have a 40A circuit breaker in your panel at the input and 16A for each group, then if one line is overloaded, only that line will shut down, and not the entire apartment.

⚠️ Attention: In apartment buildings of old buildings (before the 2000s), there is often no input circuit breaker - its role is played by a plug fuse on the landing. In this case installation of a separate machine in the apartment panel is mandatory, since plugs do not provide sufficient protection against overloads.

How to calculate the nominal value of an input machine: 3 key parameters

Choosing a machine based on current is not guessing on coffee grounds. The denomination depends on three factors:

1. Input cable cross-section - if the cable can withstand 25A, then a 32A circuit breaker will lead to overheating.
2. Total power of devices — add up the power of all devices and add 20% reserve.
3. Type of machine (B, C, D) - optimal for an apartment type C (triggered when the current is 5-10 times higher).

The calculation formula is simple: I_nom = P_sum / (U * cosφ), where:

• P_sum — total power of devices (in watts),
• U — voltage (220V for single-phase network, 380V for three-phase),
• cosφ — power factor (for household appliances ≈ 0.95).

Example: if a refrigerator (300 W), a washing machine (2000 W), a microwave oven (1500 W) and an air conditioner (1800 W) operate simultaneously in an apartment, then the total power is 5600 W. For a single-phase network: 5600 / (220 * 0.95) ≈ 26.7 A. This means you need an automatic 32A (nearest standard denomination up).

Cable cross-section, mm²	Max. current, A (copper cable)	Recommended automatic, A
2,5	27	16–20
4	38	25–32
6	46	32–40
10	70	50–63

Important: if the input cable is aluminum (in old houses), its throughput is 30% lower than that of copper. For example, a 4 mm² aluminum cable can only withstand ~25A, so a 32A circuit breaker is unacceptable for it.

Single-phase or three-phase: what to choose for an apartment

Most apartments are connected to single-phase network 220V, but in new houses or in the presence of powerful appliances (electric stove, boiler, machine) it may be necessary three-phase network 380V. How to determine what you need?

• ⚡ Single-phase input (1 automatic machine for 220V):
  • Suitable for 90% of apartments with a total power of up to 10–15 kW.
  • Easier to install and cheaper (no need for a three-phase meter).
  • Restriction: Asynchronous motors or powerful heaters cannot be connected.
• ⚡⚡⚡ Three-phase input (3 220V machines or 1 three-pole):
  • Required for power above 15 kW or devices with three-phase power supply.
  • Requires approval from the energy supply organization (often paid).
  • It is necessary to distribute the load evenly among the phases, otherwise there will be “distortion”.

Warning: if you already have a three-phase meter in your panel, this does not mean that you can arbitrarily connect three-phase machines. Any change to the input scheme requires permission from the network company - otherwise, during inspection, they may be fined or forced to redo it.

Top 5 mistakes when installing an input machine

Even experienced electricians sometimes make mistakes that later lead to accidents. Here are the most common:

1. The machine is larger than the cable allows

   Example: a 32A machine is installed on a 2.5 mm² cable, although it can only withstand 25A. Consequences: insulation melting and fire.

2. Connecting the lower terminals

   According to the PUE, power must be supplied to fixed contacts (usually the top ones). If you connect it from below, the machine will heat up and wear out faster.

3. Ignoring Selectivity

   If the rating of the input circuit breaker is equal to or less than the group value, if there is an overload, the entire apartment will turn off, not just one line. Rule: I_introductory ≥ I_group + 20%.

4. Lack of RCD/difavtomat

   The input circuit breaker only protects against short circuit and overload, but not against current leakage. For safety you need to set RCD or differential machine (with leakage current 30 mA).

5. Poor contact at terminals

   If the wire is not tightened or is not exposed enough, the connection area will heat up. Particularly dangerous for aluminum cables.

Step-by-step instructions: how to connect an input machine

For installation you will need: an automatic machine, a DIN rail, a screwdriver with an insulated handle, a cable stripper, a voltage indicator and a crimper (if you use lugs).

Step 1: Turn off the power

Check the absence of voltage using the indicator on the input cable. In apartment buildings, sometimes it is necessary to turn off the riser - coordinate this with the electrician of the management company.

Step 2. Install the machine on the DIN rail

Secure the machine to the rail by pressing the latch at the bottom of the case. For three-phase input, use a three-pole circuit breaker or three single-pole ones connected by a special strip.

Step 3: Connect the cables

• Strip the input cable 10–12 mm (for stranded wires, use ferrules NSHVI).
• Connect the phase wire (usually brown or red) to the top terminal of the circuit breaker.
• Connect the neutral wire (blue) to the neutral bus, and the ground wire (yellow-green) to the ground bus.

Step 4: Connect Output Cables

From the lower terminals of the machine, run the phase to the group circuit breakers, the zero to the zero bus (if an RCD is used, the zero also passes through it).

Step 5: Check your work

Turn on the power and check for any sparking or heating. Test the machine with the "Test" button (if available) or with a short-term load.

What to do if the machine is overheating?

If the body of the machine gets hot (more than 50°C), this is a sign of poor contact or incorrect rating. Turn off the power, check:

1. Are the terminals tightened (do not overtighten - you can break the threads).

2. Does the cross-section of the wire correspond to the rating of the machine.

3. Is there any oxidation on the contacts (clean and lubricate with a special paste).

If the problem remains, replace the machine with a better one (for example, Legrand DX³>).

Which brand of machine to choose: comparison by price and reliability

There are hundreds of models of slot machines on the market, but in terms of price/quality ratio, 5 brands are leading:

Brand	Series	Price (1p, 25A)	Pros	Cons
ABB	S200	~800–1200 ₽	High breaking capacity (6 kA), long service life	More expensive than analogues, many fakes
Schneider Electric	Acti9 iC60	~600–900 ₽	Compact, reliable contacts, has an operation indicator	The plastic body is less durable than ABB
Legrand	DX³	~500–700 ₽	Good selectivity, convenient installation	Low resistance to mechanical damage
IEK	BA47-29	~200–300 ₽	Low price, widely available in stores	Low quality plastic, frequent false alarms
KEAZ	OptiDin VM63	~300–450 ₽	Domestic brand, adapted to Russian networks	Fewer denomination selections, harder to find on sale

Advice: if your budget is limited, it is better to take KEAZ or Legrandthan cheap IEK. Savings of 200–300 rubles may result in the replacement of the machine in a year due to burnt contacts.

⚠️ Attention: Buy machines only in trusted stores (for example, 220pro.ru, asutpp.ru). In markets and small stalls, there is a high risk of running into a fake that will not work during short circuit. Original machines have holograms, clear markings and certificates.

Coordination with the management company: what you need to know

In apartment buildings, replacing or installing an input machine requires approval from the management company or energy supply organization. Here's what to do:

1. Apply in the Criminal Code indicating:
   • Reasons for replacement (for example, “a 16A circuit breaker is installed, 32A is required due to increased load”).
   • Characteristics of the new machine (brand, model, denomination).
   • A copy of your passport and title documents for the apartment.

Get permission (usually issued within 5–10 days).

Invite an electrician from the Criminal Code for sealing the meter after installation.

Important: if you replaced the machine yourself without approval, the management company can:

• Fine 1–3 thousand rubles (according to Article 7.19 of the Code of Administrative Offenses of the Russian Federation).
• Accuse him of stealing electricity (if the seal on the meter is damaged).
• Force them to dismantle the machine and return the old circuit.

Exception: if the machine is installed inside the apartment panel (not on the landing) and does not affect the common riser, approval may not be required. But it’s better to clarify this in your Criminal Code.

Frequently asked questions about entrance machines

Is it possible to install a differential machine at the input instead of a regular one?

Yes, but this is not always advisable. The difavtomat combines functions machine + RCD, but costs 2–3 times more. If the apartment already has a separate RCD for groups, a regular machine will suffice. A difavtomat is justified if:

• There is not enough space in the shield.
• Leakage protection is needed for the entire input (for example, in a bathroom with a powerful boiler).

What to do if the input machine constantly knocks out?

Causes and solutions:

• 🔌 Overload — disconnect some of the devices or install a circuit breaker with a higher rating (after checking the cable first).
• ⚡ Short circuit - Check all sockets and wires for damage.
• 🔥 Machine malfunction - replace with a new one (especially if it is cheap or old).
• 📉 Poor contact — tighten the terminals or strip the wires.

If the problem persists, call an electrician to diagnose it.

Do I need to change the machine when replacing the electrical wiring?

Yes, if:

• The cross-section of the input cable has increased (for example, from 4 mm² to 6 mm²).
• The total power of the appliances has increased (air conditioning and electric stove have been added).
• The old machine is worn out (the contacts are burnt, the body is cracked).

If the wiring and load have not changed, you can leave the old machine, but it is better to check its performance.

Is it possible to install a machine with a higher denomination than the Criminal Code allows?

No. The nominal value of the input machine is specified in the technical specifications (TU) for the apartment. If you independently install a machine at 40A instead of the permitted 25A, this will lead to:

• Overload of the general building network (neighbors will complain about voltage sags).
• A fine from the Criminal Code or energy supervision.
• There is a risk of fire if the common cable in the entrance is not designed for such current.

If you don't have enough power, you need to formally apply to increase the limit.

Which machine should I install if the apartment has a gas boiler and an electric stove?

For an electric stove, there is usually a separate line with a 32–40A automatic (depending on power). The input machine must be one step higherthan the most powerful group. For example:

• If the stove is 32A, then the input is 40A.
• If group circuit breakers: 16A (sockets) + 25A (stove) + 10A (light), then the input one is 40–50A.

For a gas boiler, a separate circuit breaker is not needed (if it is not connected to an outlet), but its power must be supplied through an RCD with a leakage current of 10 mA.