Three-Phase Power
Electrical Science · C&G 2365 Unit 302 · Free course section with an account
Domestic wiring is single-phase, but industry runs on three: three line conductors 120 degrees apart share the load and keep motors turning smoothly. Between any line and neutral you measure one ; between two lines, root three times more — in the UK, roughly 230 V and 400 V.
Star and delta connections, line versus phase quantities, and balanced-load power calculations are where Level 3 science exams concentrate, and where sign-up-and-cram revision usually falls apart. Interactive diagrams beat memorised formulas here.
Our lessons build the picture first, then drill the calculations with fresh numbers each time.
This guide is free to read. There is no public quiz specifically for this topic yet. Explore the key terms below without leaving the page.
Common questions
- Can I try Three-Phase Power free on this page?
- This guide is free to read, but there is no public quiz specifically for this topic on this page. Browse public practice samples for other subjects, or create an account for the learning path. This course section is free with an account.
- Where does Three-Phase Power sit in the City & Guilds scheme?
- Three-Phase Power maps to Unit 302. On TradeTraining it lives in the Electrical Science section as bite-size lessons with practice questions.
- Why is three-phase 400 V and single-phase 230 V?
- Both live on the same supply: 230 V is measured from one line to neutral, while 400 V is measured between two lines. The two figures differ by the square root of three, which falls out of the 120-degree spacing between phases — not from a separate, higher- source.
Explore key terms
Open a term to read its meaning here, then close it or explore another. Free to use without an account.
PSCCProspective Short-Circuit Current
The highest current that would flow in a short circuit between live conductors — line to neutral, or line to line on three-phase supplies. Together with the prospective earth fault current it makes up the prospective fault current, and the larger of the two is what switchgear breaking capacity is checked against.
Read the full PSCC glossary entryMaximum demand
The realistic peak current an installation will draw, worked out from the connected load with diversity applied. It is the figure the supply arrangements are sized against — tails, main switch, distribution equipment — and the first number a designer needs before any circuit-level decisions make sense.
Read the full Maximum demand glossary entryDiversity
The design allowance for the fact that connected loads never all run flat-out at once. A kitchen's sockets, oven and kettle sum to a huge figure on paper, but the realistic simultaneous demand is far lower. Applying diversity turns the connected load into a sensible maximum demand, keeping supplies, switchgear and cables from being absurdly oversized.
Read the full Diversity glossary entry