Wieland SNO4003K-A Safety Relay — SNO Series E-Stop / Safety Gate Monitor

Wieland Electric · SNO / SAFE Series · 24 V DC · PL e / SIL 3 · DIN-rail

The Wieland SNO4003K-A is a force-guided safety relay from the Wieland Electric SNO (SAFE) product line, used for emergency-stop monitoring, safety-gate interlock, two-hand control and downstream guarding devices such as light curtains and safety mats. The K-variant adds a "K" auxiliary monitoring contact, the 3 in the suffix denotes three enabling safety contacts, and the A-suffix marks the standard 24 V DC supply with pluggable screw terminals. It is widely deployed in mid-volume machine-building cells, packaging skids, robotic work envelopes and conveyor safety circuits where a Cat 4 / PL e / SIL 3 logic device is required.

Wieland Electric is a German industrial-electronics specialist focused on interconnection, PCB terminals, relay modules and functional-safety devices, and the SNO line is its long-running safety-control platform. Engineers commonly source the SNO4003K-A alongside Allen-Bradley Guardmaster, Siemens SIRIUS 3SK, Schneider Preventa XPS, Omron G9SA and Mitsubishi MELSEC safety modules as the upstream logic block.

1. Key Technical Specifications & Overview

The SNO4003K-A is a 22.5 mm DIN-rail safety relay with three normally-open (NO) safety contacts and one normally-closed (NC) monitoring contact. The "K" indicates an auxiliary signalling path used for cross-fault detection and EDM (external device monitoring), and the third safety contact is typically wired downstream to a second contactor in a redundant contactor pair. Cross-fault monitoring, dual-channel input evaluation and over-voltage protection are integrated, so the device can directly accept signals from mechanical E-stop pushbuttons, magnetic safety switches, non-contact safety sensors and 4-wire light curtains.

2. Application Scenarios — Where It Fits

The SNO4003K-A is engineered for the safety circuit of small-to-medium machines, where a single, certified logic device must evaluate one or more protective devices and drop out two redundant contactors. It is the typical upstream block for machine tools, packaging skids, robotic cells, conveyor guarding, light-curtain-protected workstations and presses. Below are the most common KOEED-side deployment patterns we see on customer BOMs.

• Machine tools & CNC cells — used as the E-stop and door-interlock monitor between operator guards and the main contactor pair, often paired with a Fanuc or Mitsubishi CNC front-end and a Yaskawa or Siemens servo drive.
• Robotics work envelopes — mounted in the cell cabinet as the single point of safety evaluation for light curtains, area scanners and interlocked gates, sitting in front of a Allen-Bradley GuardLogix or Omron NX/NJ safety controller.
• Packaging & bottling lines — E-stop chain on a horizontal form-fill-seal or filler, typically backed by a Panasonic FP-series PLC for non-safety sequencing.
• Conveyor & material handling — pull-cord, belt-warp and gate monitoring across a conveyor run, with a KEYENCE vision sensor or light curtain as the field device.
• Food & beverage / washdown skids — hygienic-area E-stop logic where the SNO4003K-A is sealed inside a cabinet and only IP-rated field devices are exposed.
• Two-hand control stations — configured for two-hand operation on press or punch applications, where the third NO contact is wired to the press's second contactor.

3. Integration & Wiring Notes

Wiring the SNO4003K-A follows the standard SNO / SAFE family convention: the 24 V DC supply lands on A1 / A2, the dual-channel input device (E-stop, gate switch or light curtain) lands on S11 / S12 / S21 / S22, and the three NO safety contacts (13-14, 23-24, 33-34) drive the two contactor coils in series plus an indicator. The K-monitoring contact (41-42, NC) is wired back into the safety chain as the EDM feedback, so the relay can detect a welded contactor and refuse to restart. Cross-fault monitoring is built in, meaning a short between the two input channels will be detected on power-up, which is mandatory for PL e / Cat 4.

For multi-zone machines, the SNO4003K-A is often used as the single point of evaluation for one zone, with downstream SNO4062K-A or third-party safety I/O blocks handling the rest. When the cabinet is being modernised to a Logix or TIA Portal architecture, the SNO4003K-A is kept as a stand-alone safety device: its three NO contacts feed the coil of the main contactor, and the EDM contact returns into a standard DI on the Allen-Bradley CompactLogix or Siemens S7-1200 for non-safety status mirroring. The NC auxiliary can also drive a panel indicator, a buzzer, or a non-safety input on a Panasonic FP-series PLC.

Because the SNO4003K-A is a force-guided device, contact welding on a downstream contactor will be caught by the EDM loop on the next start attempt — the relay simply will not re-energise until the fault is cleared. This is why the K-monitoring contact must never be used to switch a load directly; it is a signal contact only. For applications requiring more than three safety contacts, an SNO4062K-A (2 NO + 1 NC + delay path) or a SNO 4004K-A variant is the usual next step in the catalog.

4. Installation & Commissioning Tips

Mount the SNO4003K-A vertically on a 35 mm DIN-rail inside a cabinet with at least 10 mm of clearance above and below for airflow and wire bend. Wieland's pluggable screw-terminal blocks allow the field wiring to be pre-loomed on a bench and snapped onto the relay at commissioning, which is especially helpful on machines that have to be re-wired for export variants. Strip length, torque and ferrule size are listed on the side-label of the device — follow those values, not generic values, to keep the approvals intact.

• Confirm the 24 V DC supply is regulated and within the tolerance stated on the datasheet; an under-voltage will cause the relay to drop out without an obvious fault.
• Wire the two input channels from mechanically linked or dual-channel safety devices — a single-channel E-stop will not reach PL e.
• Loop the K-monitoring (EDM) contact back into the safety chain through the NC of each downstream contactor; if the contactor is stuck closed, the relay will refuse to restart.
• Add a 6 A fast-blow fuse on each NO contact path if driving an inductive load, sized to the Wieland derating curves.
• After wiring, perform a forced-failure test: with the machine in safe state, briefly short the input channels and confirm the relay latches off and stays off until reset.
• Document the wiring in the safety section of the machine's technical file — KOEED's FAQ page has a checklist that many integrators reuse.

For engineers working through a CE / UL re-mark, KOEED's AI Diagnostic Tool can take a photo of the existing wiring and propose a SNO4003K-A drop-in schematic, and the PLC error-code database covers the start-up blinking patterns for the SNO family.

5. Procurement, Warranty & Lead Time

The SNO4003K-A is held in our Shenzhen / Hong Kong bonded warehouse as part of the Wieland Electric safety-relay stock, and is shipped in original factory packaging (1 piece per box, factory sealed). Standard lead time is 3–5 business days for in-stock items, and 2–3 weeks for back-order or large-quantity replenishment. Worldwide shipping is available via DHL, FedEx and UPS with full export documentation, including CE / TÜV declarations of conformity on request.

KOEED is an independent multi-brand industrial-automation distributor — not the OEM — and we source the SNO4003K-A through vetted Wieland channels. Each unit is logged into our real-time sales list with date-code, lot and country of origin, so the safety file for the machine can be traced end-to-end. A 12-month functional warranty is provided on every SNO4003K-A sold, in line with our return policy.

Procurement is by RFQ, not by online check-out. Send the part list, project name and target quantity to Moritta@KOEED.COM and we will get back with availability, lead time and price within 24 hours on business days. If the SNO4003K-A is on a wider machine BOM (e.g. a Fanuc cell with Yaskawa servos and a KEYENCE vision system), send the full list to Moritta@KOEED.COM and we will quote the whole bill in one pass. A step-by-step BOM upload is also available on the Create a Quote page, and questions on the safety category or compliance can go to the same address.

For cross-brand alternatives, see the Allen-Bradley Guardmaster line, the Siemens SIRIUS 3SK family, the Omron G9SA / G9SB, the Schneider Preventa XPS, and the Mitsubishi MELSEC safety modules — all in stock at KOEED alongside the SNO series. Questions on lead time, datasheets or a bulk quote? Email Moritta@KOEED.COM and a real engineer will reply within 24 hours.