N/O vs N/C
A simple explanation of normally open and normally closed contacts and where they are used in security wiring.
What this means in practice
This page is intended to make the concept visually clear before you move into a full wiring diagram or project plan.
Quick comparison
| Term | Meaning | Typical use |
|---|---|---|
| N/O | Open until activated | Strike release trigger, gate open command |
| N/C | Closed until activated | Some safety loops, some alarm or monitored states |
| Why it matters | Wrong choice can invert device behaviour | Door may unlock when it should not, or never release |
Common mistakes
- Assuming N/O and N/C mean positive and negative.
- Wiring to the wrong relay terminal.
- Not checking the lock or gate input logic.
Where this appears in real diagrams
FAQs
Can I use this page as a final design?
No. This page is a visual explainer. Use it to understand the concept, then confirm all details against the relevant product manuals and site requirements.
What should I open next?
Open a related wiring diagram, calculator, builder, or planning pack so the concept becomes part of a real project workflow.