Introduction: why it is important to know the power of the machine in kilowatts

When choosing circuit breakers for electrical wiring in a garage, workshop or home network, many are faced with confusion between amperes and kilowatts. The current strength is indicated on the body of the machine (for example, 32A), but how to understand which power in kW is he able to withstand? This information is critical when connecting welding machines, compressors, battery charging stations or high-power lighting.

An error in calculations can lead to two extremes: the machine will trigger falsely at the slightest load (if chosen with a reserve) or, what is more dangerous, will not turn off when overloaded, causing melted wiring or a fire. This is especially true for car enthusiasts who connect equipment with high energy consumption in the garage - from inverter welders to industrial vacuum cleaners.

In this article we will look at how to accurately calculate the power for 32-amp circuit breaker in networks 220V and 380V, we will take into account demand coefficients and temperature corrections, and also draw up a compatibility table with popular garage equipment.

Calculation formula: how to convert amperes to kilowatts

To convert the current strength (I, in amperes) into power (P, in kilowatts) the Joule-Lenz law formula is used, adapted for alternating current:

For single-phase network (220V):

P = I × U × cosφ / 1000

where:

  • πŸ”Ή P β€” power in kilowatts (kW);
  • πŸ”Ή I β€” current strength in amperes (32A for our machine);
  • πŸ”Ή U β€” voltage (220V for household network);
  • πŸ”Ή cosΟ† β€” power factor (for an active load, for example, incandescent lamps or heating elements, is equal to 1; for a reactive load, for example, electric motors, ~0.8).

For three-phase network (380V):

P = √3 Γ— I Γ— U Γ— cosΟ† / 1000

Here √3 β‰ˆ 1.73 β€” root of three, taking into account the phase shift.

Calculation example for 32A machine in a single-phase network with an active load (cosφ = 1):

P = 32 Γ— 220 Γ— 1 / 1000 = 7.04 kW

However, this result is theoretical maximum. In practice, the machine operates when 80–90% of face value due to thermal characteristics, so the safe load will be ~6.5 kW.

πŸ“Š What network do you use in the garage?
Single phase 220V
Three-phase 380V
I don't know
Other

Power table for 32-amp circuit breaker

Below is a table with calculations for different types of load and networks. Values have been rounded to the nearest hundredth for convenience.

Network type Voltage (V) cosφ Max. power (kW) Recommended load (kW)
Single phase 220 1.0 (active) 7.04 6.3
Single phase 220 0.8 (reactive) 5.63 5.0
Three-phase 380 1.0 (active) 21.94 19.7
Three-phase 380 0.8 (reactive) 17.55 15.8

Please note: in a three-phase network 32A automatic withstands 3 times more powerthan in single-phase, due to the distribution of the load among the phases. This is relevant for connecting machines or compressors in car repair shops.

⚠️ Attention: If your garage has 32A input circuit breaker, this does not mean that you can simultaneously connect all devices for a total power of 22 kW (for 380V). Must be taken into account wiring cross-section and meter rating!

Why you can’t load the machine 100%

Circuit breakers have thermal and electromagnetic release. The first one is triggered when the rated current is exceeded for a long time (for example, 10–15% above 32A for an hour), the second one is triggered when there is a short circuit. Manufacturers indicate rated current (32A), but the real cutoff occurs at:

  • πŸ”₯ 1.13 Γ— Inom β€” after 1–2 hours (thermal protection);
  • ⚑ 1.45 Γ— Inom β€” instantly (electromagnetic protection).

This means that 32A automatic it will start to heat up and turn off at a current of ~36A, and at 46A it will work instantly. Therefore long-term load should be no more 32A Γ— 0.8 = 25.6A (which corresponds to ~5.6 kW in a 220V network).

Additional factors that reduce the permissible load:

  • 🌑️ Ambient temperature: in a hot garage the machine operates at a lower current;
  • πŸ”Œ Quality of contacts: Poorly tightened terminals increase resistance and heat;
  • πŸ“‰ Machine wear and tear: Over time, the bimetallic strip loses accuracy.
πŸ’‘

If the machine frequently trips for no apparent reason, check the temperature of its body with an infrared thermometer. Exceeding 60Β°C indicates overload or malfunction.

Examples of equipment for a 32-amp circuit breaker

Let's look at what equipment can be connected to 32A automatic in a garage or workshop, based on calculations:

Equipment Power (kW) Current (A, 220V) Suitable for 32A?
Welding inverter RESA TIG-200P 5.5 25 βœ… Yes (with reserve)
Compressor Fubag VCF/50 2.2 10 βœ… Yes
Electric boiler Protherm Skat 9K 9.0 41 ❌ No (needs 50A)
Charger Orion PW-320 0.8 3.6 βœ… Yes
Vacuum cleaner Karcher WD 3 1.2 5.5 βœ… Yes

For three-phase equipment (for example, metal cutting machine or industrial hair dryer) power is summed over all phases. For example, a 10 kW machine on a 380V network will require:

I = 10000 / (√3 Γ— 380 Γ— 0.8) β‰ˆ 19A

It's safe for 32A machine, but you need to make sure that the load is distributed evenly across the phases.

Check the power of the device in the passport|Check the cable cross-section (minimum 4 mmΒ² for 32A)|Calculate the total load on the line|Make sure there are no twists along the laying path-->

Common mistakes when choosing a machine

Even experienced auto electricians make mistakes when selecting circuit breakers. Here are the most dangerous of them:

  1. Ignoring inrush currents. Electric motors (for example, in compressors) consume a current of about 3–7 times higher than nominal. 32A automatic can work when you turn on a 5 kW motor if you do not use soft starters.
  2. Connecting to a machine with a smaller wiring cross-section. Cable 2.5 mmΒ² withstands ~25A, and 32A automatic - up to 36A. This will lead to melting of the insulation before the protection is triggered.
  3. Summation of capacities without taking into account the demand factor. It is unlikely that all devices will turn on at the same time. For a garage, the demand coefficient is usually taken 0.7–0.8.

Error example: installed in a garage 32A automatic, connected to it:

  • πŸ”§ Welder (5 kW, 23A);
  • πŸ’‘ Lighting (0.5 kW, 2.3A);
  • πŸ”Œ Battery charger (1 kW, 4.5A).

Total current: 23 + 2.3 + 4.5 = 29.8A β€” it seems that there is a reserve. But when starting the welder, the current briefly reaches 23 Γ— 5 = 115A, which will cause the machine to operate or damage the contacts.

⚠️ Attention: If your garage has old machine gun type AE-1031 (Soviet model), its actual cutoff may differ from modern ones VA47-29 or ABB SH200 by 10–15%. Check the technical data sheet or replace with a new one.

How to check if your machine is overloaded

If you are not sure about the correct choice of machine, follow these steps:

  1. Measure the current with a clamp. Connect all planned devices and measure the current on the phase wire. It should not exceed 25–27A for 32A machine.
  2. Check the heating. After 1–2 hours of operation, the machine should remain cold. If it is warm (more than 40Β°C), the load needs to be reduced.
  3. Use the load calculator. Online services (for example, ElectroCalc) take into account cosφ, starting currents and demand factor.

Calculation example for a garage:

  • πŸ”Œ Welder: 5 kW (cosΟ† = 0.7) β†’ 5000 / (220 Γ— 0.7) β‰ˆ 32.6A;
  • πŸ’‘ Lighting: 0.3 kW β†’ 1.4A;
  • πŸ”§ Compressor: 2.2 kW (cosΟ† = 0.8) β†’ 13.8A.

Total current taking into account the demand factor 0.7:

(32.6 + 1.4 + 13.8) Γ— 0.7 β‰ˆ 33.9A

This exceeds the safe threshold for 32A machine. Solution: distribute the load across two lines or install 40A automatic with cable 6 mmΒ².

What to do if the machine heats up without load?

If the machine heats up even when the appliances are turned off, the reason may be:

1. Poor contact at the terminals (the wires need to be tightened or stripped).

2. Poor-quality machine (replace with a branded one, for example, Schneider Electric or Legrand).

3. Phase imbalance in a three-phase network (load balancing required).

FAQ: answers to frequently asked questions

Is it possible to install a 32A breaker on a 2.5 mmΒ² cable?

No! Cable 2.5 mmΒ² designed for maximum 25A (according to PUE). For 32A machine minimum section - 4 mmΒ² (copper wire) or 6 mmΒ² (aluminium). Otherwise there is a risk of insulation melting.

Why does a 32A automatic trigger when a 4 kW welder is connected?

Welding machines have high starting currents (3–7 times higher than the nominal current). For example, 4 kW welder can consume up to 20–30A at peak, which is close to the response threshold. Solution: use a slot machine with the characteristic D (for example, C32 replace with D32) or soft starter.

How many sockets can be connected to one 32A circuit breaker?

The number of sockets is not limited - important total power connected devices. For example, to 32A automatic in a 220V network you can connect:

  • πŸ”Œ 5 sockets of 1.5 kW each (total 7.5 kW - excess!);
  • πŸ”Œ 3 sockets of 2 kW (total 6 kW - acceptable).

For a garage, it’s optimal: 1–2 sockets per tool + a separate line for lighting.

Which machine should be put into the garage if 10 kW is allocated?

For 10 kW on a 220V network:

I = 10000 / 220 β‰ˆ 45.5A

You need to choose a machine with a denomination 50A (nearest standard). Input cable cross-section β€” 10 mmΒ² (copper). If the network is three-phase (380V), it is enough 25A automatic:

I = 10000 / (√3 Γ— 380) β‰ˆ 15.2A
Is it possible to replace a 32A circuit breaker with a 40A one if the wiring holds up?

Technically possible, but only if:

  • πŸ”Ή Cable cross-section β‰₯ 6 mmΒ² (copper);
  • πŸ”Ή The meter is designed for current β‰₯ 40A;
  • πŸ”Ή There are no other weak points in the chain (for example, twists or aluminum inserts).

However, increasing the machine's denomination does not increase allocated power - this is a matter of agreement with the energy supply organization.

- Phase 1: lighting + sockets (10A automatic);

- Phase 2: welder (25A automatic);

- Phase 3: compressor + machine (20A automatic).

This is safer than one 32A circuit breaker for all equipment.-->