A coil moves a contact mechanism.

In a typical electromagnetic relay, energising the coil produces a magnetic force that moves an armature. That movement changes the state of one or more contacts. A spring returns many non-latching relays when the coil is de-energised.

The coil circuit and switched circuit are distinct. Electrical separation depends on the device’s construction and ratings; a relay is not automatically suitable for every isolation duty.

Try normally open and normally closed contacts.

For this non-latching example, “normal” means the coil is de-energised. Normally open (NO) contacts are open in that state; normally closed (NC) contacts are closed.

Coil off: NO contact open; NC contact closed.

1. Magnetic movement

Coil and spring-return armatureA conceptual linear armature moves towards the coil core when energised, against its return spring. The contact view beside it shows the resulting changeover.Coil + coreArmatureReturn springSpring holds the gap openMagnetic pull

2. Contact movement

Normally closed and normally open contactsWith the coil off, the common blade touches NC. Energising the coil moves the blade to NO. This is an idealised changeover, not a wiring diagram.CommonNCNOSame mechanism; separate circuit
  1. Coil and armature: magnetic attraction closes the air gap against a return spring. This linear sketch makes the movement visible; many relays use a hinged armature instead.
  2. Common, NC and NO: the moving blade connects the common terminal to one fixed contact. “Normal” means coil off for this non-latching example.
  3. Mechanical link, electrical separation: the armature operates the contacts. The two panels do not represent an electrical connection between the coil and switched circuit.
Use the button above to compare both states. A simplified non-latching changeover relay, not a wiring or timing diagram. Contact travel and construction vary.
Coil
De-energised
NO contact
Open
NC contact
Closed

What makes a contactor different?

Contactors are switching devices commonly designed for power loads and frequent operation, with contact and arc-management arrangements suited to their rated duties. Relays cover a broad range of signalling and switching applications.

A contactor may have main contacts for a load and auxiliary contacts used by the control system. The coil voltage says nothing by itself about the load the main contacts can switch.

Read ratings in context.

Coil rating versus contact duty

A device with a 24 V DC coil can switch a separate circuit, but only within the contact ratings and specified load duty. The coil voltage is not the switched voltage rating.

AC and DC switching, resistive and inductive loads, and starting currents can impose different demands. Two devices that physically fit need not be interchangeable.

Commands and feedback are different.

Lift controls may use auxiliary contacts to monitor a switching device. Hearing a click does not prove that every contact has changed correctly or that the connected equipment has moved.

Contacts can wear or weld. Ordinary relays should not be treated as equivalent to devices with particular monitored or safety-related characteristics.

A closer look

Latching relays can retain a state after the operating signal is removed. Solid-state relays switch electronically rather than with the moving-contact mechanism illustrated here. Neither should be assumed to behave exactly like this basic model.

Check your understanding

In the demonstration, what happens to the NC contact when the coil is energised?

Reveal the explanation

It opens. “Normally closed” describes the de-energised state of this non-latching relay, not a contact that is always closed.

Further reading.

Optional reading to explore this lesson in more detail.

  • OMRON: relay structure and operation

    Read the structure and operating-principle section. Its seven-step example follows a coil, armature and contacts; the latching-relay example then shows why not every relay resets when power is removed.