Which machine to choose for a load of 5 kW: calculation, diagrams and installation errors

Selecting a circuit breaker for the load 5 kW - a task that owners of private houses, garages and even apartments face when connecting powerful equipment. Mistakes here can lead not only to permanent power outages, but also fire due to cable overheating. This article will help you figure out which machine denomination needed for 5 kW, how to correctly calculate the wire cross-section and avoid typical installation mistakes.

Many people mistakenly believe that it is enough to take a machine gun “with a reserve” - for example, 32A instead of 25A, so that “surely it’s enough.” In practice, this approach leads to wiring overload, since the machine will not work on time, and the cable will begin to melt. Others, on the contrary, install a machine that is too “weak”, which knocks out at the slightest load. We'll figure out how to find golden mean taking into account the type of network (220V or 380V), cable length and even ambient temperature.

In the article you will find:

• 🔹 Calculation formulas machine rating for 5 kW in single-phase and three-phase networks
• 🔹 Correspondence tables power, current and cable cross-section
• 🔹 Common mistakes when choosing a machine and their consequences
• 🔹 Electrician tips for installation and connection
• 🔹 Brand overview automatic switches (from budget to premium)

1. Calculation of the machine’s rating for 5 kW: formulas and examples

To determine which machine is needed for the load 5 kW, first you need to convert power into current. To do this, we use Ohm’s law and the power formula:

For single-phase network (220V):

I = P / (U × cosφ)

where:

• I - current in amperes (A)
• P - power in watts (5000 W for 5 kW)
• U — voltage (220V)
• cosφ — power factor (for household appliances usually 0.9–0.95)

Substitute the values:

I = 5000 / (220 × 0.95) ≈ 23.9 A

This means that for the load 5 kW in single-phase network need a machine gun 25A (nearest standard denomination upward).

For three-phase network (380V):

I = P / (√3 × U × cosφ)

Let's substitute:

I = 5000 / (1.73 × 380 × 0.95) ≈ 8.1 A

An automatic machine will do here. 10A (for three-phase load). However, in reality, three-phase consumers (for example, electric motors) often have inrush currents, so you may need a circuit breaker for 16A.

2. Cable cross-section for a 5 kW machine: table and nuances

The machine protects not so much the equipment as wiring. If the cable is too thin, it will overheat before the machine operates. Therefore, the wire cross-section must correspond machine's nominal value, and not the load power.

For single-phase network (220V) with automatic 25A recommended cable cross-section:

Core material	Minimum cross-section, mm²	Maximum cable length*, m
Copper	4	up to 30
Copper	6	up to 50
Aluminum	6	up to 20
Aluminum	10	up to 30

* At ambient temperatures up to +25°C. If the cable is laid in a hot room (for example, next to a boiler), the cross-section is increased by 20–25%.

For three-phase network (380V) with automatic 16A:

• 🔸 Copper cable: 2.5 mm² (up to 20 m)
• 🔸 Aluminum cable: 4 mm² (up to 15 m)

3. Typical mistakes when choosing a machine for 5 kW

Even experienced electricians sometimes make mistakes when selecting a machine. Here are the most common:

⚠️ Attention: If you are installing an automatic 32A per cable cross-section 2.5 mm², then at a current of 30A the wiring will begin to melt, and the machine will not work - its shutdown threshold is 1.13–1.45 from nominal (i.e. 36–46A). This is a direct road to fire!

• 🔥 Automatic "with reserve": Installing a 40A circuit breaker for a 5 kW load “just in case.” Consequences: cable overheating, insulation melting, short circuit.
• ❄️ Ignoring temperature: In hot rooms (bathhouse, boiler room), the machine may operate falsely if the temperature coefficient is not taken into account.
• 🔌 Unaccounted starting currents: Electric motors (such as those in compressors or pumps) draw 3 to 5 times more current when starting. A 25A circuit breaker may not withstand a starting current of 100A.
• 🔄 Mixing aluminum and copper: Connecting an aluminum cable to the copper terminals of the machine without adapter sleeves leads to oxidation and poor contact.

Another common mistake is using cheap slot machines from unknown brands. They may have underrated characteristics (for example, a 25A circuit breaker actually only holds 20A) or unstable response time. As a result:

• 💥 False positives under minimal loads.
• 🔥 Lack of response to real overload.

What happens if you install a 16A machine instead of 25A?

With a load of 5 kW (23.9A), the 16A circuit breaker will constantly turn off, since its rating is lower than required. In addition, the contacts of the machine will begin to burn due to prolonged operation at the maximum capacity, which will lead to its failure within 1-2 months.

4. Which brand of machine to choose for 5 kW: review of manufacturers

The quality of the circuit breaker directly affects safety. We tested and analyzed reviews from electricians about popular brands:

Brand	Series	Pros	Cons	Price (25A), rub.
ABB	S200	High operating accuracy, long service life (up to 10,000 cycles)	High price, many fakes	1 200–1 500
Schneider Electric	Acti9	Good overheat protection, compact size	Plastic housing is less durable than ABB	800–1 100
Legrand	TX3	Convenient installation, wide range	Sensitive to inrush currents	700–900
IEK	KEAZ	Low price, easy to find in stores	Poor contact quality, often false positives	200–350
Eaton	PX	Long life, suitable for industrial loads	Difficult to find in retail stores	1 300–1 600

For load 5 kW in domestic conditions the optimal choice is Schneider Electric Acti9 or Legrand TX3. They strike a balance between price and reliability. For a garage or workshop where inrush currents are possible, it is better to take ABB S200 with characteristics C (it is specifically designed for loads with high inrush currents).

5. Machine connection diagrams for 5 kW: single-phase and three-phase network

Correct connection of the machine is the key to its correct operation. Let's consider two schemes:

Single-phase network (220V):

• 🔌 Phase wire (L) is connected to the top terminal of the machine.
• 🔌 Neutral wire (N) goes directly to the load (bypassing the machine!).
• 🔌 Grounding (PE) also connects directly.
• 🔌 From the lower terminal of the machine, the phase goes to the load.

Important: If an RCD is installed in the panel, it is installed after machine (in the direction of current).

Three-phase network (380V):

• 🔌 Three phases (L1, L2, L3) are connected to a three-pole circuit breaker.
• 🔌 Neutral wire (N) goes directly (if the load requires zero).
• 🔌 Grounding (PE) is connected separately.
• 🔌 Used to protect engines machines with characteristic D (they can withstand inrush currents up to 10–14 nominal values).

⚠️ Attention: When connecting a three-phase machine, make sure that the load is distributed evenly across the phases. If one phase is overloaded (for example, 4 kW at L1 and 1 kW per L2/L3), this will lead to phase imbalance and may damage the equipment.

An example of the correct connection for a garage with a load of 5 kW (single-phase network):

Shield:
1. Input circuit breaker (40A) → Counter → RCD (50A, 30mA) → 25A circuit breaker → Load (5 kW)
Cable: VVGng 3×6 (copper)

Make sure that the voltage in the network corresponds to the rating of the machine (220V or 380V)|Check the integrity of the cable insulation with a megohmmeter|Tighten the terminals of the machine with a force of 2.5 Nm (for copper wires)|Mark the phase wires (L1, L2, L3) with colored electrical tape-->

6. Frequently asked questions about choosing a machine for 5 kW

Is it possible to install a 32A circuit breaker for a 5 kW load if the cable can handle it?

No, it's dangerous. The machine must protect cable, not the load. If the cable is rated at 25A (for example, 4 mm² copper), then the 32A circuit breaker will not work at a current of 30A, which will lead to overheating of the wiring. An exception is if the cable cross-section 6 mm² and no more than 10 meters long, but even in this case it is better to use the machine for 25A with characteristics C.

What kind of machine is needed for a 5 kW welding machine?

Welding machines have high starting currents (up to 5–7 times the nominal). For a single-phase 5 kW device it is recommended:

• Automatic: 32A (characteristic C or D)
• Cable: 6 mm² copper (or 10 mm² aluminum)
• Additionally: contactor for remote control

If the welding is three-phase, an automatic machine is enough 16A with characteristics D.

What to do if a 25A circuit breaker breaks down at a load of 4 kW?

There are several reasons:

1. 🔹 Poor contact in the terminals of the machine or socket (it gets hot → thermal protection is triggered).
2. 🔹 Load fault (for example, short circuit in the motor winding).
3. 🔹 False positive due to the low quality of the machine (especially from cheap brands like IEK).
4. 🔹 Phase imbalance in a three-phase network (one phase is overloaded).

Solution: check the contacts, test the load separately, replace the machine with Schneider Electric or ABB.

Is it necessary to install an RCD along with a machine for 5 kW?

Yes, if the load is located in a room with high humidity (garage, bathhouse, basement) or it is equipment that can come into contact with a person (for example, an electric boiler). RCD parameters:

• Rated current: one step above the machine gun (for example, RCD 40A for a 25A machine).
• Leakage current: 30 mA (for human protection) or 100 mA (for fire protection).

Connection diagram: Automatic → RCD → Load.

Is it possible to use a 20A circuit breaker for 5 kW if the load is short-term?

No, even for short-term loads the circuit breaker must correspond to the maximum current. At a current of 23.9A (for 5 kW), a 20A circuit breaker will trip in 10–60 minutes due to thermal protection. If the load is really short-term (for example, starting the engine for 5 seconds), use starter with thermal relay, not automatic.