Wiring 8 — Dual-Channel E-Stop (Cat 3 Safety)
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Briefing
Category 3 (Cat 3) e-stop circuits use **two independent channels** so that a single component failure cannot prevent the machine from stopping. **Architecture:** - E-stop button has two NC contacts (CH1 and CH2). - Both channels feed separate inputs on the safety relay. - The safety relay monitors cross-faults (short between channels). - The relay output enables the machine power contactors. Wire the dual-channel e-stop to the safety relay and verify the reset circuit. ⚠️ Correctness is critical — an incorrect wiring here represents a real safety hazard.
Objectives
- Wire E-stop CH1 NC contact to safety relay input S11
- Wire E-stop CH2 NC contact to safety relay input S21
- Wire safety relay 13-14 output to enable %I0.0
- Wire reset pushbutton to safety relay S34
Hints
- Both NC contacts must open on e-stop activation for Cat 3 compliance.
- The reset button must be a deliberately actuated action — not automatic.
I/O Table
Inputs
ESTOP_CH1E-stop CH1 NC contact → safety relay S11
BOOL · %I0.0
ESTOP_CH2E-stop CH2 NC contact → safety relay S21
BOOL · %I0.1
SR_OUTSafety relay output (13-14) → PLC safe-state input
BOOL · %I0.2
RESET_PBManual reset pushbutton → safety relay S34
BOOL · %I0.3
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