---
title: "Shaded pole motor principle and characteristics"
subject: "Electric Machines II"
chapter: 3
key: "semester_5/electric_machines_ii:shaded-pole-characteristics"
source: https://www.bctengineer.com/q/semester_5/electric_machines_ii/shaded-pole-characteristics
site: BCT Engineering
---

# Shaded pole motor principle and characteristics

Electric Machines II · Chapter 3: Fractional Kilowatt Motors

- Asked in: 2082 Bhadra (new course), 2 marks
- Video: [Shaded Pole Induction Motor | Construction, Working, Torque-Speed Curve & Applications ||  BEE](https://www.youtube.com/watch?v=e4iqcSz2rnA) — Learning with Chirag
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/electric_machines_ii/shaded-pole-characteristics
- Whole chapter: https://www.bctengineer.com/md/semester_5/electric_machines_ii/chapter-3

## Question

Describe operating principle and characteristics of shaded pole single phase motor with necessary diagrams.

## Short answer

A copper shading ring on part of each salient pole causes the shaded-pole flux to lag the unshaded flux, creating a sweeping flux wave from unshaded to shaded side that acts as a weak rotating field, starting the squirrel-cage rotor in that direction. Characteristics: low starting torque (40–50% of full-load), low efficiency and power factor, fixed direction, simple construction, used in small fans, hair driers, and clocks.

## Answer

A **shaded-pole motor** is a single-phase induction motor with salient stator poles, part of each pole (about one-third) being enclosed by a short-circuited copper **shading ring**; the rotor is a squirrel cage.

```text
   +-------------+--------+
   |  unshaded   |[shaded]|  pole
   +-------------+--------+
        flux shifts  ----->
```

**Principle:** induced current in the ring opposes flux change, so the flux in the shaded part **lags** that in the unshaded part. When current rises, flux crowds into the unshaded part; near the peak it is uniform; when current falls, it crowds into the shaded part. The flux axis therefore sweeps from the **unshaded to the shaded** side, acting like a weak rotating field, and the rotor turns in that direction.

**Characteristics:**
- Low starting torque (about 40–50% of full-load torque)
- Low efficiency and power factor (ring losses)
- Fixed direction of rotation; rugged, cheap, no switch
- Used in small fans, hair dryers, toys and clocks (up to about 1/20 kW).

## Check yourself

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

1. Why does the flux in the shaded part of the pole lag?
   A. The ring is an open circuit
   B. Induced current in the short-circuited ring opposes the flux change
   C. The ring is made of iron
   D. The shaded part is longer
   Answer: B. Current induced in the shading ring opposes changes in flux, so the shaded-part flux lags that of the unshaded part. (Key point: Role of shading ring)

2. In which direction does the rotor turn?
   A. From shaded to unshaded part
   B. From unshaded to shaded part
   C. Either way, depending on the supply
   D. Opposite to the flux sweep
   Answer: B. The flux axis sweeps from the unshaded towards the shaded side, and the rotor follows this fixed direction. (Key point: Direction of rotation)

3. Which describes a shaded-pole motor?
   A. High starting torque and high efficiency
   B. Low starting torque, low efficiency and power factor
   C. Reversible by a switch
   D. Used for large drives
   Answer: B. Ring losses make efficiency and pf low, and starting torque is only about 40-50% of full load; it is limited to small loads. (Key point: Characteristics)

## Related in Electric Machines II

- [Shaded pole motor operating principle](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machines_ii%3Ashaded-pole-motor) — Electric Machines II, chapter 3
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