---
title: "Compare star and delta connection"
subject: "Basic Electrical Engineering"
chapter: 8
key: "semester_1/basic_electrical_engineering:compare-star-delta-three-phase"
source: https://www.bctengineer.com/q/semester_1/basic_electrical_engineering/compare-star-delta-three-phase
site: BCT Engineering
---

# Compare star and delta connection

Basic Electrical Engineering · Chapter 8: Three-Phase Circuit Analysis

- Asked in: 2068 Shrawan, 4 marks
- Video: [Star and Delta Connection - Explained | TheElectricalGuy](https://www.youtube.com/watch?v=-PuVmOLr5K8) — Gaurav J - TheElectricalGuy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_1/basic_electrical_engineering/compare-star-delta-three-phase
- Whole chapter: https://www.bctengineer.com/md/semester_1/basic_electrical_engineering/chapter-8

## Question

Compare the star and delta 3 phase connection.

## Short answer

Star: V_L=√3 V_ph, I_L=I_ph, neutral available. Delta: V_L=V_ph, I_L=√3 I_ph, no neutral. Both deliver same total power √3 V_L I_L cos φ in balanced conditions.

## Answer

| Basis | Star (Y) connection | Delta (Δ) connection |
|---|---|---|
| Connection | Similar ends of the three windings joined at a neutral point | End of each winding joined to the start of the next, forming a closed loop |
| Line voltage | V_L = √3 V_ph | V_L = V_ph |
| Line current | I_L = I_ph | I_L = √3 I_ph |
| Neutral | Available (3-phase 4-wire possible) | Not available (3-wire only) |
| Phase voltage | Lower (V_L/√3), so less insulation needed | Equal to line voltage |
| Phase current | Equal to line current | I_L/√3 |
| Power (balanced) | √3 V_L I_L cos φ | √3 V_L I_L cos φ |
| Use | Transmission and distribution (supplies both 230 V and 400 V); motor starting in star–delta starters | Running windings of induction motors; HV (primary) winding of distribution transformers |
| Unbalanced loads | Neutral carries the unbalanced current | No neutral; unbalanced loads give unequal line currents (third-harmonic currents circulate inside the delta) |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which connection offers a neutral point?
   A. Delta only
   B. Star
   C. Both
   D. Neither
   Answer: B. Star provides a neutral (4-wire); delta is 3-wire only. (Key point: Neutral)

2. In delta, which is true?
   A. V_L = √3 V_ph
   B. I_L = √3 I_ph and V_L = V_ph
   C. I_L = I_ph
   D. V_ph = V_L/√3
   Answer: B. Delta has V_L = V_ph and I_L = √3 I_ph. (Key point: Delta relations)

3. Why does star need less insulation per winding?
   A. Its phase voltage is only V_L/√3
   B. Its current is lower
   C. It has no neutral
   D. Its power is lower
   Answer: A. Each winding sees V_L/√3, lower than in delta. (Key point: Insulation)

4. How does balanced power differ between star and delta?
   A. Star gives more
   B. Delta gives more
   C. Same, √3 V_L I_L cos φ in both
   D. Delta gives √3 times more
   Answer: C. Both use P = √3 V_L I_L cos φ. (Key point: Power)

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