Phase voltage
The across one phase of a three-phase system. On a star-connected 400/230 V supply that's line to neutral, so 230 V. In a delta-connected load there's no star point, and each winding takes the full . Mixing the two up is an easy way to get a three-phase sum wrong.
Using Phase voltage in context
Reviewed
A distinction worth remembering
A calculation can go wrong even when the arithmetic is correct if line voltage is substituted for phase voltage. Draw the supply and load connection, label the quantities and state whether the load is balanced before choosing a formula.
Questions to take further
- How can I revise Phase voltage beyond the definition?
- Explain what Phase voltage describes, compare it with a related term and use it in a topic question. State any assumptions and what evidence you would need before applying the idea to real work.
Sources
- Professional Electrician: single-phase and three-phase power supplies (Enkin, 2024) — The basic difference between the two supplies, smoother power, higher capacity and balancing loads.
- Voltimum: basic three-phase supplies (Scolmore, 2025) — Where three-phase supplies come from: windings spaced 120° apart.
- legislation.gov.uk: Electricity Safety, Quality and Continuity Regulations 2002, regulation 27 — Declared low voltage supply of 230 V between phase and neutral in Great Britain, unless agreed otherwise.
- Professional Electrician: demand for three-phase supply in the UK (GivEnergy) — Most UK homes on a single-phase supply with one fuse, and why a battery maker says demand is growing.
- NIE Networks: connections FAQs — Northern Ireland: machines up to 17 kW on a single-phase supply, three-phase above that.
- IET: current BS 7671 edition and updates — BS 7671:2018+A4:2026 and the main subject areas updated by Amendment 4.
- Open University: relationships between electrical quantities — The relationship between voltage, current and resistance and the limits of an ohmic model.
Where Phase voltage fits in the learning path
The Electrical Science section covers these units:
- Circuit Fundamentals
Curriculum mapping: C&G 2365 Units 202/302.
See this section in the full curriculum
This section is on the free path. Lesson availability depends on content review and your learning path.
Read, practise, return
1. Read it in context
- Three-Phase PowerElectrical Science
2. Try recalling, then explore practice
Use the memory prompt below to connect the vocabulary.
- Electrical Science — quiz previewFree · Electrical Science
3. Return to the meaning
After reading or practising, explain the idea in your own words, then check what you remembered.
Recall a related term
Which term fits this definition? Say it to yourself, then reveal it. This is a memory prompt, with no score or saved result.
Voltage is the electrical potential difference between two points, measured in volts (V). It describes energy transferred per unit of charge, rather than how much charge is flowing. A battery can have voltage across its terminals even when no complete circuit exists and no current flows. Voltage and current are different quantities.
Voltage
Read the Voltage entryCompare related terms
Open a meaning to compare its role with Phase voltage, or follow its full entry.
Voltage
Voltage is the electrical potential difference between two points, measured in volts (V). It describes energy transferred per unit of charge, rather than how much charge is flowing. A battery can have voltage across its terminals even when no complete circuit exists and no current flows. Voltage and current are different quantities.
Read the Voltage entryThree-phase supply
A supply with three line conductors whose voltages reach their peaks one after another. On a standard 400/230 V system there's 400 V between any two lines and 230 V from any line to neutral. It's used for bigger loads such as motors and large boards, and the lines are identified by brown, black and grey.
Read the Three-phase supply entryLine voltage
The voltage between two line conductors on a three-phase supply: 400 V on a standard 400/230 V system. On that star-connected supply it's √3, about 1.73, times the phase voltage. People also use the phrase loosely for the 230 V on a single-phase line conductor, so check which one is meant.
Read the Line voltage entryStar-delta starter
A starter that connects a three-phase motor's windings in star to start, then changes them to delta to run. In star each winding sees less voltage, so starting current and torque are about a third of what direct delta starting gives. That means a motor needing high starting torque may not suit it.
Read the Star-delta starter entryA definition is a start. Using it in a real question is where it sticks.