# Three-Phase Power Explained: 230 V, 400 V and Neutral > Clean Markdown alternate of the published page. Canonical source: https://motorcables.co.uk/three-phase-explained/ Three-phase power is an electricity supply with three alternating voltages working in a repeating sequence. It is widely used for machinery, workshops and power distribution. This guide starts with the basics: what a phase is, why a typical UK supply offers both 230 volts and 400 volts, and what the neutral conductor actually does. You do not need an electrical background. Start with the short answer, then follow the original MotorCables diagrams below. These explain the supply principle; they are not wiring or connector assembly instructions. Is three-phase power 230 V or 400 V? On a normal UK 230/400 V supply, both voltages exist at the same time. The voltage depends on which two points you compare. Two voltages available from the same typical UK supplyBetween these pointsNominal voltage Any one phase and neutral230 V Any two different phases400 V Neutral does not switch the supply from 400 V to 230 V. A five-core supply can provide phase-to-phase power and phase-to-neutral power. Conversely, leaving neutral unused does not turn a single-phase load into a three-phase load. What does “phase” mean? Alternating current, usually shortened to AC, repeatedly changes direction. The voltage follows a repeating wave. A UK mains cycle repeats 50 times each second: this is 50 hertz, written 50 Hz. In a three-phase system, three voltage waves repeat at the same rate, but their peaks happen at different times. Each is a third of a cycle behind the previous one. Electricians describe that separation as 120 degrees. The three phase conductors are normally called L1, L2 and L3. Three waves taking turns. The labels matter more than the colours: these are diagram colours, not a cable identification chart. Open the image for a larger view. Think of three people pushing a roundabout at evenly spaced positions: their efforts are staggered. The electrical result helps three-phase motors produce a rotating magnetic field and spread a larger load across three phases. How does three-phase power get from a power station to your premises? The grid is a connected network with many sources, rather than one dedicated cable from a particular power station to your socket. In a simplified journey: Generation: a power station produces electrical energy. Other generation, including wind and solar, also feeds electricity into the network through suitable equipment. Voltage is increased: transformers raise the voltage for long-distance transmission. For the same power, a higher voltage allows a lower current, reducing heating losses in the conductors. Transmission: overhead lines on pylons carry large amounts of power at high voltage. A 400 kV line is 400,000 volts between phases, not the 400 volts used by typical workshop equipment. Voltage is reduced in stages: substations transform the voltage down through the distribution network. Local supply: a local distribution transformer typically supplies the familiar 400 V between phases and 230 V from a phase to neutral. Its low-voltage star point provides the source neutral for that local network. Do the three arms of a pylon carry three different phases? On many familiar double-circuit lattice pylons, yes: the three positions down one side carry the three phases of one circuit. The three positions on the other side usually carry a second three-phase circuit. That is two circuits with three phases each, rather than one six-phase supply. MOTORCABLES · POWER EXPLAINED One pylon. Two circuits. Three phase positions down each side Grouped wires can carry the same phase The top earthwire is not neutral Original illustrative artwork for MotorCables. Use the labelled diagram below to follow the circuit arrangement. A common arrangement, not a universal pylon layout. The labels show three phase positions per circuit; actual phase order cannot be identified from height alone. If you see two, three or four closely spaced wires hanging together at one position, those wires can form a conductor bundle. They work together as one phase; counting each wire as another phase would give the wrong answer. The smaller wire at the very top is normally an earthwire, helping protect the line against lightning; it may also contain optical fibres for communications. It is not the neutral conductor supplying your house. Other tower designs and phase arrangements exist, so position alone is not a safe way to identify a conductor. Why are four overhead wires arranged in a square? Four spaced conductors carrying the same phase form a quad bundle. They are connected in parallel and share the current. Spacers maintain the arrangement along the line. The spacing makes the group behave like a conductor with a larger effective electrical diameter for some electrical properties. This helps reduce the electric field at the wire surfaces and limit corona discharge: unwanted ionisation of nearby air that can cause power loss, noise and interference. The normal load current still flows through the metal, not through the air gaps. Those gaps do not add extra aluminium or copper. The useful comparison is a wider electrical footprint, not a solid giant cable filled with conducting air. Why not use one giant solid conductor instead of a bundle? A solid conductor as wide as the entire spaced bundle would require far more metal, making it much heavier and more costly. A single conductor with the same metal area as the bundle would be narrower and would not give the same effective electrical diameter. Bundling separates the field-control benefit from the need to fill the whole space with metal. Why can a fluorescent tube glow beneath power lines? The line’s alternating electric field can couple a small amount of energy into the tube, causing a faint gas discharge. This is electric-field or capacitive coupling, rather than the magnetic induction used in a transformer. The glow is much weaker than normal powered operation and does not mean that the air gaps inside a conductor bundle carry its normal load current. Illustrative artwork: the line’s changing electric field can make a fluorescent tube glow faintly without a wired connection. The effect is electric-field coupling, not current flowing through the air gaps between bundled conductors.Where does neutral come from? What is the star point? For a normal UK public low-voltage supply, neutral is connected to the local distribution transformer’s star point. It is not one continuous neutral wire running all the way back to the power station. A transformer changes the voltage between parts of the electricity network. Inside its low-voltage side are three sets of wire coils, called windings. In a star connection, one end of each winding meets at a common point. That meeting point is called the star point or neutral point. The other ends supply the three phases. The star point is the shared meeting point of the three transformer windings. The drawing is a simplified supply explanation, not a diagram of a plug, motor terminal block or earthing arrangement. The distributor normally connects the source neutral point to earth as part of the supply arrangement. That does not make neutral and protective earth interchangeable. In the equipment connection, neutral carries normal operating current; protective earth has a different protective purpose. Why do two 230 V phases give about 400 V, not 460 V? Because their voltage waves do not rise and fall together. Voltage between two phases is the difference between those two changing voltages. You cannot simply add their 230 V ratings. For an ideal balanced star supply, the relationship is phase-to-phase voltage = phase-to-neutral voltage × √3. The symbol √3 means the square root of three, approximately 1.732. So 230 × 1.732 ≈ 398 V: the familiar nominal 400 V system. The standard 230/400 V labels are rounded nominal values, not an exact multiplication pair or a promise of the measured voltage. Centre to a tip represents 230 V; tip to tip represents about 400 V. This is a voltage relationship diagram, called a phasor diagram. The arrows are not physical cable routes. What does the neutral conductor do? For a phase-to-neutral single-phase load, neutral provides the normal return path to the supply winding. In distribution feeding loads across all three phases, the shared neutral carries the current left over when the phase currents do not cancel. Imagine lighting on one phase, sockets on another and catering equipment on the third. They are unlikely to draw exactly the same current. Neutral supports those individual phase-to-neutral loads as their demands change. With perfectly balanced, sinusoidal three-phase currents, the currents cancel at the neutral point and neutral current is zero. That is a special condition, not a reason to remove a neutral that equipment requires. Electronic loads can also create waveform distortion, called harmonics, which can cause substantial neutral current even where phase loading appears balanced. Why do some three-phase plugs have four pins and others five? Common UK 400 V industrial connector arrangementsArrangementConductorsWhat it tells you 4-pin, 3P+EThree phases and protective earthNo neutral connection. Common for suitable three-phase loads. 5-pin, 3P+N+EThree phases, neutral and protective earthProvides neutral for equipment or distribution that requires it. Here P means phase, N means neutral and E means protective earth. Some motors need three phases and earth only; other machines also need neutral for controls or other internal loads. Check the actual equipment specification. Pin count alone does not establish voltage, current rating, clock position or compatibility. Our industrial plug standards guide explains those markings. Is taking 230 V from three-phase a voltage conversion? When a suitable 230/400 V supply has neutral available, its phase-to-neutral 230 V already exists. A correctly specified distribution assembly can make that supply available to compatible single-phase equipment; it does not necessarily contain a transformer reducing 400 V. A passive adapter cannot create a missing neutral, and protective earth must never be used as its substitute. Where only a 400 V phase-to-phase supply is available, obtaining 230 V requires an appropriate conversion arrangement rather than simply changing the connector. Current limits, protection and the equipment requirements still need to match. What about 110 V three-phase and yellow site supplies? 110 V three-phase does exist in reduced low-voltage systems, but it is a separate arrangement from ordinary UK 230/400 V distribution. The familiar single-phase 110 V site transformer output is usually centre-tapped to earth: there is 110 V between its two supply conductors and 55 V from either conductor to earth. It does not have the same line-and-neutral arrangement as a normal 230 V socket. A three-phase 110 V reduced low-voltage system instead has approximately 63.5 V from each phase to its earthed star point. Do not assume all yellow connectors or all 110 V equipment use the same arrangement. Is American three-phase 230 V? There is no single American three-phase voltage. Common examples include the following. “Wye” is the American name for a star connection. Examples of US supplies, not a compatibility guideSystemPhase to neutralBetween phases 120/208 V three-phase wye120 V208 V 277/480 V three-phase wye277 V480 V 240 V three-phase deltaDepends on the arrangement; a neutral is not always provided240 V The common US domestic 120/240 V split-phase supply is single-phase, not three-phase. US supplies commonly operate at 60 Hz, rather than the UK’s 50 Hz. An imported machine’s nameplate and instructions must be checked for voltage, frequency and phase requirements; a plug adapter does not change those characteristics. Frequently asked questions Is three-phase just three ordinary 230 V supplies? It can supply three groups of phase-to-neutral 230 V loads, but the phases have a fixed timing relationship: their waves are 120 degrees apart. Between different phases on a normal UK supply there is nominally 400 V. Does connecting neutral reduce 400 V to 230 V? No. Both voltages are already present on a normal 230/400 V supply. Phase to neutral is nominally 230 V; phase to a different phase is nominally 400 V. Neutral is not a voltage-reducing device. Does neutral come all the way from the power station? For the normal UK public low-voltage supply, neutral is taken from the local distribution transformer’s star point. It is not one continuous neutral conductor traced back through the whole transmission network to the power station. Does every three-phase machine need neutral? No. Many three-phase motors operate without neutral. Other equipment requires it for phase-to-neutral loads such as controls. Follow the equipment’s stated supply requirements rather than assuming that every three-phase connection is the same. Is neutral the same as earth? No. They have different functions in an equipment connection. Neutral is a normal current-carrying conductor; protective earth serves a protective function. Their relationship at the supply source does not make them interchangeable at a socket or appliance. Can a four-pin to five-pin adapter create a neutral? No. A passive adapter cannot create a neutral that is absent from the supply. A five-pin connector does not prove that a usable neutral is present. The complete supply and equipment arrangement must be suitable. Why do some labels say 415 V instead of 400 V? Older UK nominal descriptions used 240 V phase to neutral and 415 V phase to phase. The current nominal descriptions are 230 V and 400 V. Equipment suitability still depends on its stated operating range and other requirements. Does a 32 A three-phase supply give 96 A to one socket? No. The rating applies to each phase within the specified arrangement. The capacity of three phases cannot be pooled into one 96 A single-phase outlet by a passive splitter. Each outlet and its protection retain their own limits. Choosing a suitable lead Start with the supply voltage, available conductors, connector ratings and the equipment’s requirements. Then consider cable size, length and protection. Our voltage drop calculator includes a balanced three-phase estimate; our beginner’s voltage drop guide explains what the results mean. For cable construction and markings, see Arctic PVC and H07RN-F cable explained. For help selecting an assembly, send MotorCables your supply details, equipment requirements and required length. Sources and technical notes The explanations and original MotorCables graphics describe typical arrangements, not every supply system or installation. Voltages are nominal AC root-mean-square values, shortened to RMS. RMS describes the effective voltage; it is not the instantaneous peak of the wave. Fingrid: fluorescent lamps and the electric field beneath transmission lines. EMFs information service: electric-field effects on fluorescent tubes. NPTEL Power System Analysis: bundled conductors, spacers and corona. National Grid: the transmission journey and voltage changes. National Grid: conductor bundles and the overhead earthwire. National Grid: identifying tower circuits, conductor bundles and the earthwire. Schneider Electric Electrical Installation Guide: standard voltages and phase-to-neutral versus phase-to-phase notation. Schneider Electric: the transformer star connection and neutral point. OpenEnergyMonitor: three-phase timing, voltage geometry and motor principles. Its historical 240/415 V example illustrates the same square-root-of-three relationship. IET Wiring Matters: the distribution transformer star point and neutral. Schneider Electric: balanced currents, harmonics and neutral loading. IET Wiring Matters: reduced low-voltage systems and HSE: construction-site 110 V supplies. Phoenix Contact: US split-phase, wye and delta supply examples. Mennekes: industrial connector markings and configurations. Technical sources checked 4 November 2026. Diagrams created for MotorCables. Two voltages available from the same typical UK supply Between these points Nominal voltage Any one phase and neutral 230 V Any two different phases 400 V Illustrative artwork: the line’s changing electric field can make a fluorescent tube glow faintly without a wired connection. The effect is electric-field coupling, not current flowing through the air gaps between bundled conductors. Where does neutral come from? What is the star point? Common UK 400 V industrial connector arrangements Arrangement Conductors What it tells you 4-pin, 3P+E Three phases and protective earth No neutral connection. Common for suitable three-phase loads. 5-pin, 3P+N+E Three phases, neutral and protective earth Provides neutral for equipment or distribution that requires it. Examples of US supplies, not a compatibility guide System Phase to neutral Between phases 120/208 V three-phase wye 120 V 208 V 277/480 V three-phase wye 277 V 480 V 240 V three-phase delta Depends on the arrangement; a neutral is not always provided 240 V