Uploaded March 2026 | Updated September 2026, 3 weeks ago
Is your PLC stop circuit fail-safe? See why a normally-open stop button fails on a broken wire, rewire it, and edit the P1-M622-16DR program live — no downtime.
⚡ QUICK ANSWER
A stop button wired normally-open is not fail-safe: if that wire breaks or works loose, the PLC never sees the stop signal, and the stop button silently stops working — a dangerous failure. The fail-safe fix is to wire the stop button normally-closed, so the input is normally true and pressing the button (or a broken wire) opens the circuit and stops the machine. That means the ladder logic changes too — the stop contact becomes normally-open in the program to match the inverted wiring. On the P1-M622-16DR you can make this change live with online editing, updating the running program without stopping the machine, then test that both a button press and a disconnected wire now stop it. The full wiring and step-by-step edit are in the written guide below.
📖 FULL STEP-BY-STEP + DOWNLOADS (wiring diagram, project file, screenshots)
accautomation.ca/p1-m622-16dr-plc-learn-now-online-editing-and-fail-safe-wiring
⏱️ TIMESTAMPS
0:00 - Introduction: Online Editing & Fail-Safe Wiring
1:07 - Current Wiring Configuration Review
1:51 - Demonstrating the Problem — NOT Fail-Safe
3:06 - The Ladder Logic Problem
3:28 - Understanding Fail-Safe Wiring
4:43 - Rewiring the Stop Button (Normally-Closed)
6:45 - Online Editing — Making the Change Live
8:44 - Testing the Fail-Safe Circuit
📚 WHAT YOU'LL LEARN
✅ Why a normally-open stop button isn't fail-safe (a broken wire disables it)
✅ How normally-closed wiring makes a stop circuit fail on the safe side
✅ Why the ladder logic must change to match the inverted wiring
✅ Make the change live with online editing — no downtime
✅ Test that both a button press and a broken wire now stop the machine
❓ FREQUENTLY ASKED
Q: Why isn't a normally-open stop button fail-safe?
A: If the wire to a normally-open stop button breaks, the PLC never receives the stop signal, so the button silently stops working. A normally-closed stop is normally true, so a broken wire stops the machine instead. The full explanation is in the guide.
Q: How do you wire a fail-safe stop button?
A: Wire it normally-closed so the input is on during normal operation; pressing the button — or a broken/disconnected wire — opens the circuit and stops the machine. The ladder logic contact changes to match.
Q: What is online editing on the P1-M622-16DR?
A: It lets you modify the ladder program while the PLC is running, so you can apply a change like this without stopping the machine or losing outputs.
👉 Full step-by-step & wiring diagram: accautomation.ca/p1-m622-16dr-plc-learn-now-online-editing-and-fail-safe-wiring
🔗 MORE RESOURCES
▶ Series: accautomation.ca/series/productivity-plc
▶ P1-M622-16DR — Wiring & Testing a Start-Stop Circuit: youtu.be/q4f8KC2CJOQ
▶ Productivity Mini PLC Timer Instructions: youtu.be/Hl9-X4cxuxQ
▶ PLC Beginners Guide: accautomation.ca/programming/plc-beginners-guide
▶ Free eBooks: accautomation.ca (subscribe for download)
🛒 RECOMMENDED HARDWARE
▶ Shop: automationdirect.com
▶ Parts Guide: accautomation.ca/purchase-find-parts
💬 Questions? Drop a comment below.
🔔 New tutorials every Monday — Subscribe and hit the bell!
#PLC #LadderLogic #IndustrialAutomation #PLCProgramming #ACCAutomation #ProductivityPLC #AutomationDirect #FailSafe #MotorControl #LearnPLC
Regards,
Garry
ACC Automation
accautomation.ca
Is your PLC stop circuit fail-safe? See why a normally-open stop button fails on a broken wire, rewire it, and edit the P1-M622-16DR program live — no downtime.
⚡ QUICK ANSWER
A stop button wired normally-open is not fail-safe: if that wire breaks or works loose, the PLC never sees the stop signal, and the stop button silently stops working — a dangerous failure. The fail-safe fix is to wire the stop button normally-closed, so the input is normally true and pressing the button (or a broken wire) opens the circuit and stops the machine. That means the ladder logic changes too — the stop contact becomes normally-open in the program to match the inverted wiring. On the P1-M622-16DR you can make this change live with online editing, updating the running program without stopping the machine, then test that both a button press and a disconnected wire now stop it. The full wiring and step-by-step edit are in the written guide below.
📖 FULL STEP-BY-STEP + DOWNLOADS (wiring diagram, project file, screenshots)
accautomation.ca/p1-m622-16dr-plc-learn-now-online-editing-and-fail-safe-wiring
⏱️ TIMESTAMPS
0:00 - Introduction: Online Editing & Fail-Safe Wiring
1:07 - Current Wiring Configuration Review
1:51 - Demonstrating the Problem — NOT Fail-Safe
3:06 - The Ladder Logic Problem
3:28 - Understanding Fail-Safe Wiring
4:43 - Rewiring the Stop Button (Normally-Closed)
6:45 - Online Editing — Making the Change Live
8:44 - Testing the Fail-Safe Circuit
📚 WHAT YOU'LL LEARN
✅ Why a normally-open stop button isn't fail-safe (a broken wire disables it)
✅ How normally-closed wiring makes a stop circuit fail on the safe side
✅ Why the ladder logic must change to match the inverted wiring
✅ Make the change live with online editing — no downtime
✅ Test that both a button press and a broken wire now stop the machine
❓ FREQUENTLY ASKED
Q: Why isn't a normally-open stop button fail-safe?
A: If the wire to a normally-open stop button breaks, the PLC never receives the stop signal, so the button silently stops working. A normally-closed stop is normally true, so a broken wire stops the machine instead. The full explanation is in the guide.
Q: How do you wire a fail-safe stop button?
A: Wire it normally-closed so the input is on during normal operation; pressing the button — or a broken/disconnected wire — opens the circuit and stops the machine. The ladder logic contact changes to match.
Q: What is online editing on the P1-M622-16DR?
A: It lets you modify the ladder program while the PLC is running, so you can apply a change like this without stopping the machine or losing outputs.
👉 Full step-by-step & wiring diagram: accautomation.ca/p1-m622-16dr-plc-learn-now-online-editing-and-fail-safe-wiring
🔗 MORE RESOURCES
▶ Series: accautomation.ca/series/productivity-plc
▶ P1-M622-16DR — Wiring & Testing a Start-Stop Circuit: youtu.be/q4f8KC2CJOQ
▶ Productivity Mini PLC Timer Instructions: youtu.be/Hl9-X4cxuxQ
▶ PLC Beginners Guide: accautomation.ca/programming/plc-beginners-guide
▶ Free eBooks: accautomation.ca (subscribe for download)
🛒 RECOMMENDED HARDWARE
▶ Shop: automationdirect.com
▶ Parts Guide: accautomation.ca/purchase-find-parts
💬 Questions? Drop a comment below.
🔔 New tutorials every Monday — Subscribe and hit the bell!
#PLC #LadderLogic #IndustrialAutomation #PLCProgramming #ACCAutomation #ProductivityPLC #AutomationDirect #FailSafe #MotorControl #LearnPLC
Regards,
Garry
ACC Automation
accautomation.ca
