• 12 parts
  • Checked September 2026

Parts of a Motor Starter

A magnetic motor starter in its enclosure, and the contactor cut through.

Parts of a Motor Starter

Name Date

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1 2 3 4 5 6 7 8 9 10 11 12
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Write the name of each numbered part.Answer key

  1. Enclosure
  2. Contactor
  3. Auxiliary contacts
  4. Overload relay
  5. Heater
  6. Reset button
  7. Start button
  8. Stop button
  9. Coil
  10. Armature
  11. Movable contacts
  12. Stationary contacts

Drawn for this site on 2026-09-30 from plain geometry. Licence: own work.

Each numbered ring is a button. Use the arrow keys to move between them and Enter to choose. Names are read out in Study, and once a part is answered.

Next step Next: the parts of an electric motor

All 12 parts on the diagram

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Starter 8

  1. Enclosure The metal box that houses the starter.
  2. Contactor The switch, worked by an electromagnet, that connects the motor.
  3. Auxiliary contacts Small extra contacts, worked by the contactor, for the control circuit.
  4. Overload relay It opens the control circuit if the motor draws too much current.
  5. Heater An element in each power wire that the motor current heats.
  6. Reset button Pressed to reset the overload relay after it has tripped.
  7. Start button Pressing it energizes the coil and starts the motor.
  8. Stop button Pressing it breaks the circuit to the coil and stops the motor.

Inside the contactor 4

  1. Coil The winding of the electromagnet. Current in it pulls the armature.
  2. Armature The iron piece the electromagnet pulls. It carries the movable contacts.
  3. Movable contacts Contacts that travel with the armature.
  4. Stationary contacts Fixed contacts, joined to the wires in and out.

How this list was compiled: Every name checked on 2026-09-30 and kept only where at least two of these use it. (1) Wikipedia, Magnetic starter, https://en.wikipedia.org/wiki/Magnetic_starter , with Contactor, Motor controller and Relay: a contactor and an overload relay; the starter coil; heaters; an enclosure; start and stop buttons; power contacts and auxiliary contacts; moving and fixed contacts; armature. (2) US Navy, Electrician's Mate 3 & 2, Rate Training Manual, full text at https://archive.org/details/ERIC_ED110703 : contacts of the main contactor, heaters of the overload relay, operating coil, reset button, stationary contacts, auxiliary contacts, START and STOP buttons. (3) US Navy, IC Electrician 3 & 2, Rate Training Manual, full text at https://archive.org/details/ERIC_ED106514 : a contactor's operating coil, armature and main contacts; stationary and movable contacts. (4) W. N. Alerich, Electric Motor Control (1983), search passages at https://archive.org/details/electricmotorcon00aler : coil, armature, stationary contacts, movable contacts, auxiliary contacts, overload relay and heater, reset button, enclosure, start button. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; no maker's tool, nothing traced. Licence: own work

How it works

A magnetic motor starter is a switch worked by an electromagnet, with overload protection added. The motor starter components here are the contactor, the overload relay and what is inside each.

Read the full guide

Contactor and overload relay

A starter is two blocks in an enclosure. The upper one is the contactor, the switch that connects the motor. The lower one is the overload relay. It has a heater in each power wire and a reset button. A start button and a stop button control the starter.

Inside the contactor

The coil is wound round an iron core. Current in the coil draws the armature to the core. The armature carries the movable contacts, which close on the stationary contacts and connect the motor.

  • The stationary contacts are also called fixed contacts, and the coil the operating coil. The quiz takes either.

Questions and answers

What are the parts of a motor starter called?

A magnetic motor starter is a contactor plus an overload relay in an enclosure. The contactor has a coil, an armature, and stationary and movable contacts. The overload relay has heaters and a reset button.

How does a contactor differ from a motor starter?

A contactor is the switch alone. A motor starter is a contactor with an overload relay added, so it protects the motor as well as switching it.

What do the heaters in a motor starter do?

Each heater carries the current of one power wire. If the motor draws too much current for too long, the heat trips the overload relay. The relay opens the circuit to the coil and the contactor drops out.

What is the reset button on a motor starter for?

After the overload relay trips, its contacts stay open. Pressing the reset button closes them again once the relay has cooled.

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