Is it possible to install a 25A circuit breaker on a 2.5 mm² wire?

No. The maximum permissible circuit breaker for a 2.5 mm² copper cable is 20A, but for complete safety (especially in wooden houses) 16A is recommended.

Which machine for a 3 kW water heater?

The current consumption of a 3 kW heater is about 13.6A. The closest rating of the machine is 16A. The recommended cable is VVGng 3x2.5.

What does the letter C mean on a machine (for example, C16)?

The letter C denotes the tripping characteristic. Type C circuit breakers can withstand moderate inrush currents (5-10 times the rated value) and are ideal for apartment sockets.

Selection of circuit breaker

⚡ How to choose a machine and protect the wiring

The correct selection of a circuit breaker is a matter of fire safety. The machine does not protect household appliances, but the cable inside the wall.

⚠️ The main rule of an electrician: The rating of the machine must be less than the maximum permissible current of the cable. If you put a 25A circuit breaker on a weak wire, if there is an overload, the insulation will melt faster than the protection will work.

Instructions for the calculator

Load power: Sum up the power of all devices on the line (in kW).
Network type: 230V (regular socket) or 400V (three-phase network).
Safety factor: We recommend leaving 20% (factor 1.2) so that the machine does not “knock out” with each power surge.

🧮 Calculation example

Suppose we connect equipment with a power of 5.5 kW to a three-phase network (400V) with cos φ = 0.95.

Больше по теме: Cable cross section calculator

Section⚡ How to determine the cable cross-section by diameter Our tool helps to accurately determine the cross-sectional area of the core, knowing its diameter.

Bay📏 How to find out the length of the cable without unwinding the coil? The tool solves the main problem of warehouse accounting and installation: it determines the remaining wire on a drum or in a coil.

Current formula: I = P / (√3 × U × cosφ)
Calculation: 5500 / (1.732 × 400 × 0.95) = 8.36 A
Add a margin of 20%: 8.36 × 1.2 = 10.03 A
Result: Choose the closest denomination upward - 16A.

If you are installing wiring yourself and purchasing materials, check the wire footage using the tool calculation of cable length in a bay.

Frequently asked questions (FAQ)

🔹 Is it possible to install a 25A machine on a 2.5 mm² wire?

Strongly not recommended. Although a 2.5 mm² cable (GOST) can withstand up to 27A in an open way, it gets hotter in the wall. Safety standard: on a 2.5 mm² cable - 16A automatic (maximum 20A). For a 1.5 mm² cable (light) - 10A automatic.

🔹 Which machine is needed for a water heater or washing machine?

Usually these are powerful devices (2–3 kW). For them, a separate line is laid with a 2.5 mm² cable and an automatic machine with a nominal value of16Ais installed. If there are several devices, use our calculator to accurately sum up the power.

🔹 What do the letters B, C, D mean on the machine?

This is the time-current characteristic (sensitivity to inrush currents).

B - for old wiring and lighting (works quickly).

C - the most popular, for apartments and offices (moderate delay).

D - for machines and motors with high starting currents.

🔹 Which power factor (cos φ) should I choose?

For apartments (heating elements, lamps, kettles) set 1.0 or 0.95. For electric motors, pumps, and machine tools, the value is usually indicated in the passport (about 0.7–0.8). If in doubt, visit our electrics section for other calculations.