CoilCurrent through it turns the core into a magnet.
CoreSoft iron. It becomes a magnet while the coil is on.
ArmatureThe moving iron bar. The magnet pulls it down to the core.
PivotThe hinge the armature rocks on.
SpringIt pulls the armature back when the current stops.
Movable contactIt moves with the armature, from one fixed contact to the other.
Normally closed contactTouching while the coil is off; open while it is on.
Normally open contactApart while the coil is off; closed while it is on.
Coil terminalsThe two pins that carry the control current to the coil.
Common terminalThe pin joined to the movable contact.
How this list was compiled: Every name checked on 2026-09-30, each in both sources: (1) US Navy, Navy Electricity and Electronics Training Series (NEETS), Module 3, Introduction to Circuit Protection, Control, and Measurement, public domain, https://archive.org/details/NEETSModule03 (a relay consists of a magnetic core and its coil, contacts, springs, armature and the mounting; figure 3-19 names the armature, the pivot, the common terminal and the relay coil terminals; the energized coil pulls the armature to one contact and opens the other; movable contacts; make and break contacts; normally open and normally closed; a small current switches a large one through the contacts); (2) Wikipedia, Relay, text only, https://en.wikipedia.org/wiki/Relay (a coil wound on a soft iron core, an iron yoke, a movable iron armature hinged to the yoke, a spring that returns it, moving and fixed contacts, normally open and normally closed contacts, the common terminal, the coil terminals). Licence: own work
The drawing: Drawn for this site on 2026-09-30 from plain geometry; nothing traced. Licence: own work
How it works
The parts of a relay make a switch that is worked by a magnet. The drawing shows a simple relay with its cover off and its coil switched off, so the spring holds the armature up.
Read the full guide
The magnet and the moving bar
Numbers 1 to 5: the coil and the core inside it, the armature across the top, the pivot it rocks on and the spring on its tail. Switch the coil on and the core pulls the armature down; switch it off and the spring lifts it again.
The contacts and the pins
Numbers 6 to 10: the movable contact on its blade, the normally closed contact it rests against, the normally open contact below it, the two coil terminals and the common terminal.
Normally means with the coil off. A normally closed contact is touching then; a normally open contact is not.
Questions and answers
What are the main parts of a relay?
A coil on an iron core, a movable iron armature, a spring and one or more sets of contacts. The coil and core make an electromagnet. The armature carries the movable contact, and the spring holds it back until the coil is switched on.
How does a relay work?
A small current in the coil makes the core a magnet. The magnet pulls the armature, which moves the movable contact from one fixed contact to the other. When the current stops, the spring pulls the armature back.
What do NO and NC mean on a relay?
NO is normally open: a contact that is apart while the coil is off and closes when it is on. NC is normally closed: a contact that is touching while the coil is off and opens when it is on.
Why use a relay instead of a switch?
A relay lets a small current switch a large one. Light control wires run to the coil, and only the contacts carry the heavy current, so the power can be switched from a distance.