What Is an 8-Pin Relay? Pinout and How the Coil Flips the Contacts
A relay is a part where current through the coil flips all of its contacts at once. One small signal switches several circuits simultaneously. More importantly, this "coil moves the contacts" idea is the shared backbone of nearly every part on the practical exam — MC · EOCR · timer · FLS · FR. The only thing that changes is what turns the coil on.
They share one 8-pin socket
On the exam, the 8-pin relay, timer, FR, and FLS all use the same 8-pin socket. The pin layout is identical, so any of them drops into the same slot. That's why you nail down the 8-pin numbering first.
Pinout — coil on 2·7, two contact sets
Pins are numbered from the bottom-right, counter-clockwise: 1 → 8, keyed off the notch at the bottom center.
- Coil: 2 · 7 — apply voltage across these two and the relay pulls in.
- First contact set: 1 (COM) · 3 (a/NO) · 4 (b/NC)
- Second contact set: 8 (COM) · 6 (a/NO) · 5 (b/NC)
Each contact set has three pins — common (COM) · NO · NC. At rest, COM sits on the NC contact.
Energize the coil, and the contacts move
- Rest — coil de-energized, COM resting on NC.
- Energized — coil on, COM swings to NO. Both sets move together — one signal switching two circuits at once. That is the whole point of a relay.
What turns the coil on — part by part
Same structure, different trigger. This one table explains half the parts on the exam.
| Part | What energizes the coil |
|---|---|
| 8-pin relay · MC | A person pressing a button, or a signal from another circuit |
| EOCR | Trips itself when motor current exceeds the setpoint |
| Timer (T) | Acts a set delay *after* the coil is energized |
| FLS | When the tank electrodes are submerged |
| FR (flicker) | Once powered, its contact toggles on a fixed cycle |
Next
The most important circuit you build from this relay is the self-holding circuit — a relay holding its own coil energized through one of its own contacts. It's the backbone of every exam control circuit. If contacts and push-buttons are still fuzzy, start with Sequence control basics.
Try it yourself
See the 8-pin relay switch in the Korean Electrician practical simulator →