When it comes to connecting powerful equipment in a garage, workshop or production line, the question “63A how many kilowatts 3 phase” becomes critically important. An incorrect calculation can lead to constant operation of the machine, overheating of the wiring, or even a fire. In this article we will figure out how to accurately determine the maximum power for a three-phase 63 ampere machine, taking into account all the nuances: from the network voltage to the power factor of the equipment.
Many motorists and owners of small businesses are faced with the need to connect a welding machine, compressor or machine with three-phase power. At the same time, the standard approach of “installing a bigger machine” often leads to problems. We'll show you why 63A in three-phase network - this is not just 13.86 kW (as many people think), but a value that can vary from 22 to 43 kW depending on conditions. You will learn how to avoid mistakes when choosing a cable, why it is important to take into account inrush currents and how to correctly distribute the load across phases.
Why 63A ≠ 13.86 kW: debunking myths about power
The most common mistake is to use the formula for a single-phase network (P = U × I) to three-phase systems. As a result we get 13.86 kW (220V × 63A), which is fundamentally wrong for 380V. Correct calculation requires taking into account several factors at once:
- 🔹 Line voltage (380V between phases, not 220V phase-zero)
- 🔹 Power factor (cos φ) equipment - from 0.7 to 1.0
- 🔹 Load symmetry by phase (uneven distribution reduces permissible power)
- 🔹 Temperature conditions (a 63A circuit breaker at +40°C only holds 57A)
Basic formula for a three-phase network: P = √3 × U × I × cos φ. Under ideal conditions (cos φ=1, symmetrical load, 20°C) we get 43.4 kW. But in reality this value is always lower. For example, for a welding machine with cos φ=0.7, the power will be only 30.4 kW - almost 30% less than the “theoretical maximum”.
Power table for a 63A machine at different cos φ coefficients
To avoid doing calculations manually, use a ready-made table. Please note that the values are for symmetrical load at a temperature of 20°C. In real conditions, the permissible power should be reduced by 10-15%.
| cos φ | Maximum power (kW) | Typical Equipment |
|---|---|---|
| 1.0 | 43.4 | Electric boilers, heating elements, lighting |
| 0.95 | 41.2 | Asynchronous motors (75% load) |
| 0.85 | 36.9 | Welding transformers, compressors |
| 0.7 | 30.4 | Welding inverters, pumps |
| 0.6 | 26.0 | Woodworking machines |
It is important to understand that starting currents can be 3-7 times higher than nominal. For example, a 15 kW engine consumes up to 105 kW at startup, which will instantly trigger a 63A automatic. In such cases it is required:
⚠️ Attention: For equipment with high starting currents (compressors, pumps), use machines with the characteristic D (not C), which have a delay. For example, ABB S203 D63 or Schneider Electric C63N D.
How to properly distribute the load among phases?
Uneven load distribution is one of the main reasons for tripping of 3-phase circuit breakers. Even if the total power does not exceed 40 kW, but one phase is loaded at 30 kW and the other two are loaded at 5 kW, the machine will turn off. Follow these rules:
Measure the current of each phase with clamps (the difference should not exceed 20%)
Connect single-phase consumers >5 kW to different phases
Use baluns for uneven loads
Check the distribution after each new connection -->
For clarity, consider an example from a garage workshop:
- 🔧 Phase A: Welding machine (10 kW, cos φ=0.7) → 21.7A
- 🔧 Phase B: Compressor (5.5 kW, cos φ=0.85) + Lighting (1 kW) → 13.5A
- 🔧 Phase C: Lathe (7.5 kW, cos φ=0.8) → 16.9A
Total current: 21.7 + 13.5 + 16.9 = 52.1A (within 63A). But if you connect the welder and the compressor to the same phase, the current will reach 35.2A, which will lead to imbalance and possible tripping of the machine.
For accurate monitoring, use a three-phase ammeter with data logging, e.g. Fluke 179 or UNI-T UT210E>. These devices show the current in each phase in real time and help avoid overloads.
Selecting a cable for a 63A machine: cross-section and materials
The machine protects not the equipment, but cable. Therefore, the cross-section of the wires must correspond to a current of 63A with a margin. For three-phase networks, use the following recommendations:
| Core material | Minimum cross-section (mm²) | Recommended cable |
|---|---|---|
| Copper | 16 | VVGng 5×16, NYM 5×16 |
| Aluminum | 25 | AVVGng 5×25 (only for stationary installation) |
Key points when choosing a cable:
- 🔌 For moving connections (e.g. to a mobile compressor), use flexible cables KG 5×16 or PVS 5×16
- 🔌 In fire hazardous areas (garages, workshops), be sure to take cables with the index ng (non-flammable)
- 🔌 Use armored cables for laying in the ground VBBShv 5×16
⚠️ Attention: If the cable length from the machine to the equipment exceeds 50 meters, it is necessary to take into account voltage drop. For 63A and a length of 100m, the losses will be ~5%, which can cause unstable operation of the equipment. In such cases, increase the cross-section to 25 mm² (copper) or use local transformers.
Practical example: connecting a welding station
Let's consider a real case of connecting a welding station in a car service. We have:
- 🔥 Welding inverter Resanta SAI-220 (220A, PV=30%, cos φ=0.7)
- 🔥 Plasma cutter Fubag Plasma CUT 60 (60A, 380V)
- 🔥 Ventilation system (3 kW)
Step 1: Calculate the power of the welder at 30% PV (operating mode):
P_welding = 220A × 25V × √(0.3) × 0.7 ≈ 8.6 kWStep 2: Add a plasma cutter (15 kW) and ventilation. Total: 8.6 + 15 + 3 = 26.6 kW.
Step 3: Checking the current:
I = 26600 / (√3 × 380 × 0.85) ≈ 48AConclusion: 63A machine is suitable with a reserve. However, when simultaneous work welder and plasma cutter at maximum modes, the current can reach 60A, which is close to the limit. Solution:
Connection diagram optimization
1. Separate the welder and plasma cutter into different phases
2. Set the machine to 80A with characteristic D
3. Use a balun to balance the load
4.Add a contactor to cut off the ventilation during welding
Common mistakes and how to avoid them
Even experienced electricians sometimes make mistakes when working with three-phase networks. Here are the most critical ones:
- Ignoring cos φ - many take the coefficient 1.0 “by eye”, although for welders it is often 0.6-0.7
- Ignoring starting currents — engines at the moment of startup consume 5-7 times more than the nominal value
- Phase imbalance — connection of powerful single-phase consumers to one phase
- Wrong choice of machine - characteristic C instead of D for equipment with high inrush currents
- Saving on cable - use of aluminum instead of copper or lower cross-section
Case study: a compressor was installed in one car service center ABAC Bambi 200 (15 kW) for a 63A automatic machine with a 10 mm² cable. When first started, the cable heated up to 80°C, and the machine worked after 3 minutes. The reason is the starting current of 90A and the undersized cable cross-section (16 mm² was needed).
Always check the equipment datasheet for inrush currents (Inrush Current) and choose a machine with characteristic D for motors and compressors.
FAQ: Answers to popular questions
Is it possible to connect a 36 kW electric boiler to a 63A automatic?
Theoretically, yes, since 36 kW at cos φ=1 gives a current of 57.7A (36000/(√3×380)). However:
- Use a slot machine with characteristics C (not D), since boilers do not have high starting currents
- The cable cross-section must be at least 16 mm² (copper) or 25 mm² (aluminum)
- Make sure that the input machine and meter are designed for such a load
Why does a 63A circuit breaker trip at a load of 30 kW?
There are several reasons:
- Uneven load across phases (for example, 25 kW on one phase and 5 kW on the other two)
- Low cos φ of equipment (for example, 0.6 instead of 0.8)
- High ambient temperature (the machine in the panel heats up above 40°C)
- Starting currents (if motors or compressors are connected)
Use current clamps to diagnose real consumption for each phase.
Which machine should I put on a 3-phase 200A welding machine?
For welder Resanta SAI-200 or similar:
- Rated current: 200A at PV=35%
- Real power: ~7.5 kW (200×25×√0.35×0.7)
- Recommended machine: 80A characteristics D (for example, IEK BA47-63 D80)
- Cable cross-section: 25 mm² copper or 35 mm² aluminum
Important: connect welders via power outlet (for example, 32A 380V) with a separate automatic machine.
Is it possible to replace a 3-phase 63A circuit breaker with three single-phase 25A ones?
Technically possible, but not recommended for reasons:
- There is no protection against phase imbalance (one phase may be overloaded, others may not)
- It is more difficult to ensure selectivity (disabling only the problematic phase)
- Three-phase circuit breakers have a mechanical connection of levers - in the event of a short circuit, all phases are switched off simultaneously
Exception: if you are protecting three independent single-phase lines (for example, lighting, sockets, ventilation), then such a solution is acceptable.
How to check if the 63A circuit breaker is overheating under load?
Use pyrometer or thermocouples:
- Load the network by 80% (for example, 50A for a 63A machine)
- After 1 hour, measure the temperature of the machine body:
- ✅ Normal: up to 50°C
- ⚠️ Warning: 50-70°C (check contacts)
- ❌ Critical: above 70°C (replace the machine)
For regular monitoring, install current transformer with ammeter (for example, CARLO GAVAZZI WM14-300).