In a schematic, what does the relay coil symbol indicate and how does it relate to the contact symbol?

In a schematic, what does the relay coil symbol indicate and how does it relate to the contact symbol?

• A. The coil represents an electromagnet; when energized, it actuates the corresponding contact, changing its state (normally open closes; normally closed opens).
• B. The coil is a passive resistor that does not affect contacts.
• C. The coil indicates an alternating current source.
• D. The coil is a mechanical latch with no electrical function.

Answer: (A)

Relays use an electromagnet to switch contacts. The coil symbol shows a winding that, when current flows through it, creates a magnetic field strong enough to move the relay’s armature. That motion is what changes the state of the contact symbol. In a typical relay, one contact is drawn as normally open and another as normally closed. By default (coil de-energized), the normally closed contact is closed and the normally open contact is open. When the coil is energized, the NO contact closes and the NC contact opens. The coil and the contacts are mechanically linked, so energizing the coil drives the same mechanism that changes the contacts’ states. Often a dashed line or bracket is used in schematics to show this linkage. So the coil symbol indicates the driving element that actuates the contact when energized.

Relays use an electromagnet to switch contacts. The coil symbol shows a winding that, when current flows through it, creates a magnetic field strong enough to move the relay’s armature. That motion is what changes the state of the contact symbol. In a typical relay, one contact is drawn as normally open and another as normally closed. By default (coil de-energized), the normally closed contact is closed and the normally open contact is open. When the coil is energized, the NO contact closes and the NC contact opens. The coil and the contacts are mechanically linked, so energizing the coil drives the same mechanism that changes the contacts’ states. Often a dashed line or bracket is used in schematics to show this linkage. So the coil symbol indicates the driving element that actuates the contact when energized.