Pilz PNOZ s4 vs PNOZ X3: Safety Relay Wiring Schemes & E-Stop Architecture

Functional machine guarding requires fail-safe evaluation of emergency stop pushbuttons, safety gates, and optical light curtains. Pilz PNOZ safety relays set the global benchmark for Category 4 / PLe (ISO 13849-1) and SIL 3 (IEC 62061) compliant emergency stop circuits.

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1. Comparing PNOZcompact (s4) with Classic PNOZ (X3)

Specification	Pilz PNOZ s4 (750104 / 751104)	Pilz PNOZ X3 (774310 / 774318)
Housing Width	Ultra-slim 22.5 mm	Standard 45.0 mm
Safety Contacts	3 N/O instantaneous + 1 N/C auxiliary	3 N/O safety + 1 N/C auxiliary + 1 Semiconductor
Supply Voltage	24 VDC (Electronic power regulation)	24 VDC / 110-230 VAC multi-voltage options
Terminals	Push-in spring or screw terminals	Screw terminals
Operating Modes	E-stop, safety gate, light curtain (OSSD)	E-stop, safety gate (Monitored or automatic start)

Explore safety hardware and contactors on the AOCTRL Pilz Safety Catalog and AOCTRL Safety Automation Hub.

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2. Dual-Channel E-Stop Wiring with Cross-Fault Detection

To achieve Category 4 architecture:

1. Wire dual N/C contacts across terminals S11-S12 (Channel 1) and S21-S22 (Channel 2).
2. The relay outputs pulsed test signals on S11 and S21. A short circuit between channels is instantly detected, dropping safety output contacts 13-14, 23-24, and 33-34.
3. Wire feedback loop from downstream contactors into Y1-Y2 (PNOZ s4) or S33-S34 (PNOZ X3) for contact weld monitoring.

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3. Procurement of Certified Safety Spares

Avoid production line shutdowns by sourcing factory-sealed Pilz, SICK, and Banner safety relays directly through AOCTRL Industrial Sourcing.