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

bandzior2 202514 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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  • #31 5778055
    neo_dc
    Level 32  
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    In my opinion, the thermal switch must have been faulty, something could have been wrong with the motor itself (bad centration, maybe one phase burned out). Unless you cut logs of wood there for half a day, the equipment for almost 700 PLN would be expected to work with reasonable use.

    The thermal switch, even without protective zero, should work properly.
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  • #32 5840356
    MW-750
    Level 12  
    Posts: 19
    Rate: 13
    I returned the engine to the service under warranty and I have already picked up a new one, because the factory has given a new engine under warranty. It was not written in the warranty what happened to the old one, only the entry "replacement of the engine with a new one". I didn't change anything in the power cable. I started the saw with a new motor and it ran without any problems for the whole day of cutting (the previous motor about an hour then died). Not once did it turn off on the thermal sensor. The engine warmed occasionally, but not as much as the previous engine. If it goes on like this, it's OK. Thanks again to everyone for the advice.
  • #33 5842304
    Duszek100
    Level 11  
    Posts: 16
    NS! phase 1 L2 phase 2 and L3 phase 3 4 wire is N and the fifth is for powering the lamps

    Added after 25 [seconds]:

    all clear
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  • #34 5852765
    ektryk-ko
    Level 10  
    Posts: 22
    Rate: 2
    L1, L2, L3 or as it used to be called R, S, T are phases, N is a "working" conductor in single-phase devices, but ... here to souls100 - since when can anything be powered with the fifth conductor? This cord is never working. I can see that everything is not very clear to you. The fifth conductor is the PE protective conductor. Ask your uncle google about such a wire and then maybe it will be clearer to you.
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  • #35 5960069
    Przemski1
    Level 15  
    Posts: 202
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    I have read a lot here on a very good topic. but to be sure, I will ask.
    If I have a 230V welder with a very thick power cable (two wires with a diameter of about 2mm) that cannot be installed in an ordinary plug because it is too large and melts plastic, can I install the plug under the power socket and connect only two pins there: one phase and zero? ??
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  • #36 5960179
    neo_dc
    Level 32  
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    Yes, you can do that :)
  • #37 5960303
    bandzior2
    Level 26  
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    Only in the power plug you have 5 pins. 3 lean phases, 1 skinny hedge, and one thick zero. So you have to connect one to the phase and one to the zero.
  • #38 5961055
    Przemski1
    Level 15  
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    http://pl.wikipedia.org/wiki/Przew%C3%B3d_elektryczny


    N is the so-called zero wire that goes from the pole anyway! ??

    PE is a wire that is connected to the pins protruding from the sockets and then connected to the ground yes! ??

    PEN is a wire that is connected to the so-called zero from the pole and the pin protruding from the socket (grounding) yes! ??

    Do I think right?
  • #39 5961177
    bandzior2
    Level 26  
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    Let's say on a 230V installation. This N is our zero, PE is the ground. PEN is where there is no grounding and is connected to N.
  • #40 5961214
    Przemski1
    Level 15  
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    I think well
  • #41 5975016
    Przemski1
    Level 15  
    Posts: 202
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    and I have a problem, I connected one wire to zero, the other to one phase to different, I tried and the welder does not work and by inserting wires from it to a regular socket it works without any problems
    The current to the power socket passes through an old type switch with a left-right switch, is it something that may be disturbing?
    I checked if there is current in the power socket and it is on 3 phases because the fourth is zero and I have no idea what it is about.
  • #42 5976620
    bandzior2
    Level 26  
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    The right-left switch is to change only one of the phases. Example. You have 3 phases in socket 1 2 and, for example, your motor is running clockwise. If you want to the right, you have to switch one of the phases. 1 3 2 and it's already getting you left. So there should be no difference in the operation of the welding machine.
  • #43 5981788
    ektryk-ko
    Level 10  
    Posts: 22
    Rate: 2
    Check if there is N in the power socket. The right-left switch only switches the phase sequence and N should be directly. If the right-left switch is functional and the zero is disconnected, all 3-phase receivers will work properly in such a connection, but there will be no N in the plug, so there will be no N on the housing. For safety reasons, in such a case, the device housing should be grounded to this plug connected. However, if you use 1 of the phases and N from this socket, then when it is not connected directly in the right-left switch housing, you do not have N in the socket. In this case, nothing 1-phase did.
  • #44 5989943
    Przemski1
    Level 15  
    Posts: 202
    Rate: 36
    Well, just removing the cover from the switch, right left, I see that N goes directly to the power socket, it does not pass through the switch. What needs to be done for it to work?
  • #45 5994782
    ektryk-ko
    Level 10  
    Posts: 22
    Rate: 2
    Since you write that the welder works in socket 230, it receives 1 of the phases and N. You also write that by connecting this welder to socket 400 in the way you describe it does not work, there is a simple error somewhere. There are 3 phases and N to the power socket, and if it is a newer type of installation, then PE. There must be no phase in the 400V socket that you are using to connect the welding machine or it must not be zero (N). There's no other way. Try to replace the phase used to connect the welder to another one.
  • #46 5994896
    neo_dc
    Level 32  
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    take the bulb holder, 2 wires and connect to one phase and N. When it lights up, it means that something is kicked in the case, if not, it means that there is either no phase or zero (it burned out somewhere along the way).
  • #47 16873735
    carlos2384
    Level 10  
    Posts: 85
    Rate: 10
    Hello

    I have a similar question :) at home, I would like to connect a cryptocurrency excavator that has a 1.2kW power supply, at home I have 4 phases and fuses like in the picture. My point is whether the installation will withstand the connection of such a device and possibly the maximum number of such devices that can be connected to this installation, the monthly kWh consumption by household appliances is about 260
  • #48 16873753
    Freddy
    Level 43  
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    carlos2384 wrote:
    I have 4 phases at home
    I wonder where you got the 4 phases from :)
  • #49 16873841
    carlos2384
    Level 10  
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    I know there are normally 3, but that's what the owner of the apartment said, so I wrote :) maybe from the photo you can understand what he meant :)
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    • Understanding 230V & 380V Current Phases: Wiring, Voltages, and Changing Direction of Power Motor IMG_20171129_002308.jpg (2.34 MB) You must be logged in to download this attachment.
  • #50 16873981
    zster

    Level 28  
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    carlos2384 wrote:
    I know there are normally 3, but that's what the owner of the apartment said, so I wrote


    It was talking nonsense. You have 3 phases, but this in the context of the question has virtually no meaning. 1.2kW is a pimple. The first better electric kettle is> 2kW.
    How many devices can be connected depends on what else works on individual circuits and whether they would be connected to the same circuit.
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  • #51 16874025
    carlos2384
    Level 10  
    Posts: 85
    Rate: 10
    Well, the power itself is like a pimple, but I also read that you look at it differently when something works 20 minutes and different when non-stop :) and how to check what circuit it is connected to?
  • #52 16874056
    Rafael22
    Level 21  
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    230V * 16A = 3680W = max 3.68kW on one circuit
    230V * 10A = 2300W = max 2.3kW on one circuit

    I assume that
    16A is for sockets where there should be a 2.5mm2 cable, the load capacity of which is about 21A (it depends on the number of wires, whether in a pipe or in plaster, etc.)
    10A is for lighting where there should be a 1.5mm2 cable, the load capacity of which is about 16A
  • #53 16874060
    carlos2384
    Level 10  
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    I know that :) but I mean how to check which circuit to which room it is :) unless I screwed something up :)
  • #54 16874073
    Freddy
    Level 43  
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    carlos2384 wrote:
    I meant what circuit to which room it is
    It is best to call the fortune teller :)
    Think a little - turn off one by one and watch where the light goes out :D
  • #55 16874081
    Rafael22
    Level 21  
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    carlos2384 wrote:
    I know that :) but I meant what circuit to which room it is :) unless I screwed something up :)


    It's simple, leaving one fuse on, turning off the others and checking where the electricity is. There does not necessarily have to be one fuse for one room, it depends how someone did it. These three connected together, the main protection probably cuts off the electricity everywhere, either to a power socket as you have, or to an induction hob or something similar that needs 400V max 16A
  • #56 16874166
    rafbid
    Level 33  
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    Freddy wrote:
    Think a little - turn off one by one and watch where the light goes out
    Actually, lighting and sockets should be on separate circuits :D
  • #57 16874191
    carlos2384
    Level 10  
    Posts: 85
    Rate: 10
    Well, I didn't think about disconnecting :) and seriously, I thought that somehow it goes differently :) but as far as i know, the kitchen is with the room where the excavator is supposed to be :) I currently have an induction hob in the kitchen and an electric oven, but originally there was an electric cooker in the kitchen that looked like a traditional gas oven :)
  • #58 16874207
    rafbid
    Level 33  
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    carlos2384 wrote:
    as far as I know, the kitchen is with the room where the excavator should be :)
    You must be sure.
    carlos2384 wrote:
    I currently have an induction hob in my kitchen and an electric oven
    The oven is on the same circuit as the induction hob?
  • #59 16874209
    carlos2384
    Level 10  
    Posts: 85
    Rate: 10
    I think I did not connect it, only an electrician

    Added after 3 [minutes]:

    I'm sure the kitchen and the excavator room are on the same fuse
  • #60 16874224
    rafbid
    Level 33  
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    You can turn off this triple fuse and check.
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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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