Electrical wiring in the garage is not just a convenience, but a safety issue. Improperly sized circuit breakers (CBs) can result in fire, equipment damage, or even electric shock. Many car owners mistakenly believe that it is enough to install a “bigger machine” so that it does not “knock out” when welding or a compressor is working. In fact, this approach only increases risks.

In this article we will look at what machines to put in the garage taking into account the type of wiring, equipment power and the requirements of the PUE (Electrical Installation Rules). You will learn how to calculate the rating of the machine, which type (B, C or D) to choose for garage conditions, and why RCD or differential machine often become mandatory. We will also analyze typical installation errors and provide a checklist for self-installation.

Why you can’t put “any” machines in the garage

A garage is a room with high humidity, dust and the risk of mechanical damage to wiring. Powerful equipment is often used here: welding machines, compressors, chargers, and sometimes mini-machines. Conventional household machines for 16–25 A, which are located in apartments, are not always suitable for a garage.

The main risks of making the wrong choice:

  • 🔥 Fire due to cable overheating (if the machine does not respond to overload).
  • ⚡ Short circuit when working with powerful consumers (if the machine is not designed for inrush currents).
  • 💡 False positives (if the machine is too sensitive for garage conditions).
  • 🛠️ Equipment damage (for example, combustion of the compressor winding during voltage surges).

In addition, they are often used in the garage aluminum wiring (especially in old buildings), which requires a special approach to protection. The machine must operate before the cable begins to melt - this is the main safety rule.

Types of garage machines: B, C or D?

Circuit breakers are divided into classes according to time-current characteristic (VTH). Three types are suitable for the garage:

Machine type Response range What loads is it suitable for? Recommendations for the garage
B 3–5 × Inom Lighting, sockets for household appliances Suitable for garages without powerful equipment (for example, only lighting + battery charging).
C 5–10 × Inom Medium loads: compressors, grinders, drills The optimal choice for most garages. Withstands inrush currents.
D 10–20 × Inom High starting currents: welding machines, powerful machines It is necessary to install only on separate lines for such equipment.

Example: if there is a garage welding machine 5 kW, then you need to install an automatic machine on its line D (for example, D25), and is suitable for lighting and sockets C16.

📊 What type of machine is in your garage?
Type B
Type C
Type D
Don't know/no machines

Calculation of machine denomination: formulas and examples

The machine's nominal value depends on equipment capacity and cable cross-section. Use two formulas:

  1. By power: I = P / U, where P — total power (W), U — voltage (220 V).
  2. By cable cross-section: there must be a machine below maximum cable current (see table PUE 1.3.4).

Calculation example for a garage with:

  • Lighting (300 W),
  • Compressor (2.2 kW),
  • Charger (500 W).

Total power: 300 + 2200 + 500 = 3000 W.

Current: 3000 / 220 ≈ 13.6 A.

Select the machine on 16 A (nearest higher denomination). But if the cable has a cross-section of 1.5 mm², its maximum current is 19 A, so 16 A is suitable.

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

If the cable is designed for 16 A, then when overloaded it will start to heat up, but the 25 A circuit breaker will not work. This will lead to melting of the insulation and the risk of fire. It is especially dangerous for aluminum wiring, which degrades faster when heated.

Important: if in the garage three-phase network (380 V), the calculation is carried out using a different formula: I = P / (U × √3 × cosφ), where cosφ — power factor (usually 0.8).

Wiring diagrams for machines in the garage

In the garage, two schemes are usually used:

  1. Single-level (one machine for everything).

    Suitable for small garages with minimal equipment. Minus: when triggered, everything turns off.

  2. Multi-level (group).

    Optimal for garages with several lines (lighting, sockets, powerful equipment). Example:

  • 💡 Line 1: Lighting - automatic B10.
  • 🔌 Line 2: Sockets - automatic C16.
  • ⚡ Line 3: Welding machine - automatic D25 + RCD 30 mA.

For a three-phase network, the circuit is complicated by adding three-pole circuit breakers and four-pole RCDs.

Check the cable cross-section on each line

Calculate the total power of the equipment

Select machine type (B, C or D) from the table

Install an RCD for wet areas and powerful appliances

Label machines (for example, “Light”, “Sockets”, “Welding”)

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RCDs and differential circuit breakers: are they needed in the garage?

RCD (residual current device) Must be installed in a garage if:

  • 🚗 There are metal surfaces (car body, workbench) that may be energized.
  • 💦 High humidity (condensation, puddles on the floor).
  • ⚡ Portable power tools are used (drill, grinder).

The rating of the RCD is chosen one step higher than the machine. Example: if the machine C16, then the RCD - 25 A / 30 mA.

Differential automatic (automatic device + RCD in one housing) is convenient for individual lines, but more expensive. It is placed on:

  • Welding machine line.
  • Sockets for outdoor garage lighting.
  • Portable extension cords.
⚠️ Attention: The RCD does not protect against short circuits! It's always put after machine, and not instead of it.

Typical mistakes when choosing and installing machines

Even experienced car owners make mistakes. Here are the most dangerous:

  1. Automatic “with a reserve”.

    Installation C32 instead of C16 “just in case” leads to overheating of the cable. The machine must protect the weak link in the chain - the cable, not the equipment.

  2. Ignoring inrush currents.

    Compressors and welding machines consume 3-5 times more current when starting up. Automatic type B will trigger falsely.

  3. No RCD in wet areas.

    A garage with a dirt floor or no heat is at higher risk of electrocution.

  4. Aluminum + copper without adapters.

    Direct connection of aluminum and copper cable leads to oxidation and heating.

Another common mistake is connecting bugs (jumpers instead of machines). This violates the PUE and can lead to a fire.

1) Are there any overloaded extension cords (“tees”)?

2) Is the cable insulation intact (especially at bend points).

3) Are there too powerful devices connected to the same line?

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Step-by-step instructions for installing machines

If you decide to install the machines yourself, follow this algorithm:

  1. Turn off the power on the input panel (check the absence of voltage with an indicator screwdriver).
  2. Install DIN rail in the shield (if it is not there).
  3. Secure the machines on the rail, starting with the introductory one.
  4. Connect phase (L) on top of the machine, zero (N) - on the tire.
  5. Connect the RCD (if any) after the machine, but before the load.
  6. Label the lines (for example, tags or marker).
  7. Check your work alternately switching on the load.

For a three-phase network:

  • Use three-pole circuit breakers.
  • Observe the color coding: L1 - brown, L2 - black, L3 - gray.
  • There must be an RCD four-pole.
⚠️ Attention: If the garage is connected to the network via old style counter (with a seal), changing the scheme yourself may be considered a violation. In this case, coordination with the energy supply organization is required.
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The main installation rule: the machine must break a phase, not a zero! Connecting a zero to the machine is unacceptable and dangerous.

FAQ: Frequently asked questions about machines in the garage

Is it possible to use machines like A or K?

No. Type machines A designed to protect semiconductor devices (for example, power supplies), and type K — for loads with high starting currents (motors). The optimal types in the garage B, C or D.

Which machine should I put on the line to charge the battery?

For a charger (with a power of up to 1 kW), an automatic machine is sufficient B10 or C10. If you are using a powerful charger (for example, for truck batteries), calculate the current using the formula and select an automatic one with a 20% margin. For example, for charging at 2 kW: 2000 / 220 ≈ 9 A → automatic C10.

Is grounding necessary in the garage if there are RCDs?

The RCD is triggered by a current leak, but does not replace grounding. In a garage, grounding is required for:

  • Metal equipment casings (welder, compressor).
  • Sockets for outdoor use.
  • Shields with a metal body.

Without grounding, the RCD may not operate if the insulation breaks down on the housing.

What to do if the machine is overheating?

Reasons for heating the machine:

  1. Poor contact at terminals (screws need to be tightened).
  2. Line overload (check the power of connected devices).
  3. Low-quality machine (replace with a branded one: ABB, Schneider Electric, Legrand).

If the heat is strong (burns your hand), turn off the power immediately and replace the machine!

Can I use home machines in my garage?

Yes, but with reservations:

  • Home machines (for example, IEK or EKF) suitable for garages with light load (lighting, sockets for tools).
  • For powerful equipment (welding, machine tools) it is better to use industrial machines (for example, Schneider Acti9), since they are designed for frequent operation.