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Understanding 230V & 380V Current Phases: Wiring, Voltages, and Changing Direction of Power Motor

bandzior2 202583 61
Best answers

Why is a three-phase outlet 400V instead of 3×230V, and why does swapping any two phases reverse a three-phase motor?

A three-phase outlet is 400V phase-to-phase because you measure voltage between two different phase conductors, and the three 230V phase waveforms are shifted by 120°, so they do not add up to 690V; the old 380V/220V values were simply updated to 400V/230V [#5372492][#5372516][#5378606] The neutral conductor comes from the transformer’s star point, while the protective conductor (PE) is separate ground; in older 4-wire systems that protective conductor may be absent, while newer installations use L1, L2, L3, N, PE [#5372492][#5717177] A three-phase motor works because the three phase currents create a rotating magnetic field, so swapping any two phases changes the phase sequence and reverses the field’s rotation, which reverses the motor direction [#5378606][#5717177] Motor wiring depends on its rating plate: a motor with 400V windings can often be connected in delta for 400V and in star for a different voltage, but a motor designed for 230V coils must not be connected in delta at 400V [#5375683][#5720958] The total power can be the same for single-phase and three-phase equipment, but three-phase reduces current in each conductor and therefore eases cable and fuse loading [#5744205]
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  • #61 16874228
    carlos2384
    Level 10  
    Posts: 85
    Rate: 10
    How is it spr turning off everything ??
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  • #62 16874611
    Rafael22
    Level 21  
    Posts: 383
    Help: 42
    Rate: 172
    carlos2384 wrote:
    how is it spr turning off everything ??


    Do it this way:
    keep all single fuses on and trip the triple off
    This way you will check what this triple is for. If the induction hob and the oven do not work and there is electricity in the sockets in the kitchen and other rooms, you will know that it is only for induction and the oven, or the induction itself or something else.
    Then turn on the triple one and turn off the first single one and check where you have no electricity, then turn on the first one and turn off the second one, etc.
    The first two should only turn off the light, or so it seems after the value of the fuses.

    There is no other easy way to turn off the fuse.
    You don't want to tear cables off the wall :D
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Topic summary

✨ The discussion revolves around the understanding of 230V and 380V current phases, particularly in relation to wiring configurations, voltage levels, and the operation of three-phase motors. Key points include the clarification that the phase-to-phase voltage in a three-phase system is 400V, while the voltage between phase and neutral is 230V. The necessity of changing one phase to reverse the direction of a motor is explained through the concept of phase shift in the alternating current (AC) waveforms. The conversation also touches on the implications of connecting devices to different voltage systems, the importance of grounding, and the differences between star and delta connections in motors. Additionally, users share experiences with specific devices, troubleshooting issues, and the significance of thermal switches in motor operation.
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FAQ

TL;DR: 400 V three-phase delivers 73 % more voltage than a 230 V single phase, enabling the same 3 kW motor to pull 42 % less current [Elektroda, neo_dc, post #5372492] "Voltage is a potential difference" [Elektroda, neo_dc, post #5375683]

Why it matters: This FAQ helps DIYers and tenants safely tap 230 V or 400 V, size cables, and reverse motors without frying tools or fuses.

Quick Facts

• EU nominal voltages: 230 V phase-to-neutral, 400 V phase-to-phase (IEC 60038). • Voltage tolerance: −10 %/+5 % ⇒ 207–241.5 V RMS [Elektroda, Paweł Es., post #5378606] • Current per 16 A socket: max ≈ 3.7 kW at 230 V [Rafael22, #16874056]. • Star vs delta: star lowers coil voltage by √3 (≈ 42 %) [Elektroda, neo_dc, post #5720958] • Single-phasing can overheat windings in <5 min and trip thermals [Elektroda, Paweł Es., post #5744205]

Why isn’t 3 × 230 V equal to 690 V in a 400 V socket?

The three phase waveforms are 120 ° apart; vector addition gives √3 × 230 V ≈ 400 V, not simple addition [Elektroda, neo_dc, post #5372492]

How do I reverse a three-phase motor’s direction?

Swap any two phase conductors in the plug: L1↔L2, L1↔L3, or L2↔L3. The 120 ° sequence changes, so the magnetic field spins the other way [Elektroda, Paweł Es., post #5378606]

Do I need the neutral (N) wire for a star-connected motor?

Not for a balanced three-phase motor; currents cancel in the neutral, so it can remain disconnected [Elektroda, Quarz, post #5384937]

What happens if one phase drops out (single-phasing)?

The motor stalls, draws up to 6× nominal current, overheats, and may burn windings within minutes [Elektroda, Paweł Es., post #5744205]

Which cable size for a 3.7 kW (16 A) circuit?

Use 3×2.5 mm² Cu (plus PE) for sockets; its ampacity ≈ 21 A in-wall, meeting 16 A breaker requirements [Rafael22, #16874056].

Is a 3 kW, 400 V motor ‘stronger’ than a 3 kW, 230 V motor?

Power is identical, but the 400 V unit draws ≈ 7.5 A versus 13 A at 230 V—thinner cables, cooler fuses [Elektroda, Paweł Es., post #5744205]

Why did my saw’s thermal sensor never trip before the motor failed?

Likely a faulty thermal cut-out or mis-wired sensor. Lack of PE does not block thermal operation [Elektroda, neo_dc, post #5778055]

How do I adapt a 5-pin plug to a 4-wire (old TN-C) supply?

Bridge PE to N inside the socket, connect the three phases, and label the outlet; this meets TN-C rules but offers limited shock protection [Elektroda, neo_dc, post #5717177]

Can I ground equipment by driving my own earth stake?

Yes, but the rod must reach low-resistance soil (<30 Ω). Verify with an earth-tester; ad-hoc stakes rarely pass inspection [BS 7671].

How many 1.2 kW cryptocurrency rigs can one 16 A socket handle?

At 230 V, 16 A supplies 3.68 kW, so safely two rigs (2.4 kW) per circuit, leaving 1.3 kW headroom [Rafael22, #16874056].

Quick 3-step test to map breakers to rooms?

  1. Switch off all branch breakers except one.
  2. Check which lights/sockets still work.
  3. Label the breaker and repeat for each circuit. This avoids guesswork [Freddy, #16874073].

Edge case: what if neutral opens but PE remains?

Appliances can see full 400 V across live and floating parts, blowing electronics and risking shock—use PEN bonding or RCDs to mitigate [IEC 60364].

Is the fifth pin in a 400 V plug ever a live conductor?

No. It is always PE (protective earth); live conductors are the three slim pins, and N (if present) is thicker [Elektroda, bandzior2, post #5960303]

What’s the legal voltage range I should measure at my sockets?

European low-voltage networks must stay within 207–253 V; frequent deviations merit a utility report [Elektroda, Paweł Es., post #5378606]
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