Key Technical Specifications
| Parameter | Value |
|---|---|
| Model | P1U-1NB/230V-/2U |
| Manufacturer | Pilz |
| Product Type | Safety / Monitoring Relay |
| Supply Voltage | 230–250 VAC |
| Monitored Power Range | 3.5–1100 VA |
| Output Current Rating | 8 A |
| Mounting | DIN rail (verify with mechanical drawing) |
| Safety Standards | EN ISO 13849-1 / IEC 62061 (verify specific PL/SIL rating with OEM datasheet) |
| Application Domain | Voltage/power monitoring, machine safety circuits |
| Condition | Surplus / Obsolete stock |
Product Introduction
Monitoring relays sit in the background of a safety circuit doing one job: watching a parameter and pulling the plug when something goes wrong. The Pilz P1U-1NB is one of those workhorse devices — a voltage/power monitoring relay rated for 230–250 VAC supply, covering a monitored power range of 3.5 to 1100 VA, with an 8 A output contact. It was designed to sit in a Pilz safety circuit and flag abnormal conditions before they become equipment damage or personnel injuries.Pilz built its reputation on safety relays that fail safe — meaning when the relay itself develops an internal fault, the output drops out rather than sticking closed. The P1U series follows that philosophy. What engineers valued about this unit was the wide VA monitoring window, which gave flexibility across different machine sizes without needing to stock multiple relay variants. One thing to keep in mind: this is an older generation Pilz product. The PNOZsigma and myPNOZ lines have largely absorbed its role in modern installations, but for maintaining legacy machines, this relay is still the correct replacement part.
Quality SOP & Tech Pitfalls
The Lab Report (SOP)
Here’s what should happen before this relay ships:
- Visual/Counterfeit Inspection: Verify Pilz branding, model marking (P1U-1NB/230V-/2U), and part number legibility. Check for rework signs or non-OEM labeling.
- Physical Inspection: Examine the housing for cracks, heat discoloration, or terminal damage. Verify DIN rail clip integrity.
- Contact Resistance Check: Use a multimeter (Fluke 115 or equivalent) to verify output contact continuity in both energized and de-energized states.
- Functional Test: Apply rated 230 VAC supply, simulate an out-of-range condition, and confirm the relay trips and the safety output opens within the specified response time.
- Insulation Resistance Test: Measure insulation resistance between supply terminals and output contacts to confirm isolation integrity.
- Anti-static Packaging: Seal in ESD-safe packaging for shipment.
The Engineer’s Warning (Pitfalls)
- Mismatching the VA range. The P1U-1NB monitors a 3.5–1100 VA window. If your application’s actual load sits near the upper or lower edge of that range, you’ll get nuisance trips or missed faults. Verify the actual VA draw of the monitored circuit before installing this relay — don’t assume the old relay’s settings were correct.
- Forgetting to document the DIP switch or potentiometer settings. Older Pilz monitoring relays often have adjustable thresholds set by physical pots or DIP switches. I once watched a maintenance team spend four hours chasing a “faulty” relay that was actually set to the wrong trip point because the previous tech never documented the adjustment. Photograph the settings before pulling the old unit.
Installation & Configuration Guide
- Pre-Installation (⚠️ Safety First)
- Lock out and tag out all power sources feeding the safety circuit and the monitored load.
- Verify zero energy state with a calibrated multimeter.
- Photograph the existing relay’s position, wiring connections, and all adjustment settings (pots, DIP switches, or jumpers).
- Removal
- Label each wire connected to the relay terminals (supply, monitored circuit, output contacts).
- Disconnect all wiring.
- Release the DIN rail clip and remove the old relay.
- Installation
- Before seating the new P1U-1NB, replicate all DIP switch and potentiometer settings from the old unit onto the replacement. This step prevents the majority of startup failures.
- Snap the relay onto the DIN rail and confirm it locks securely.
- Reconnect all wiring per your labels and photographs.
- Power-On & Verification
- Restore supply voltage (230–250 VAC) and verify the relay powers up.
- Check the output contact status — it should be in the normal (non-tripped) state under healthy conditions.
- Simulate a fault condition (e.g., disconnect the monitored load or apply an out-of-range voltage) and confirm the relay trips and the safety output opens.
- Restore normal conditions and verify the relay resets correctly.
- Run the machine through a full operational cycle before returning to production.
Compatible Replacement Models
| Model | Compatibility Tier | Notes |
|---|---|---|
| P1U-1NB/230V-/2U | ✅ Drop-in Replacement | Same part number — direct swap, replicate adjustment settings |
| P1I-1NB/115V~/2U | ⚠️ Software Compatible | Same series but 115 VAC supply — requires supply voltage change; verify circuit compatibility |
| PNOZsigma monitoring variants | ⚠️ Verify with OEM | Modern Pilz monitoring relays may cover the same function but require wiring changes and logic reconfiguration |
| Third-party monitoring relays | ❌ Hardware Mod Required | Different pinout, safety architecture, and certification — not recommended for safety circuit substitution |
Frequently Asked Questions (FAQ)
Q: Is the P1U-1NB still being manufactured by Pilz?
Based on available information, this part appears to be discontinued/obsolete. Stock availability is limited to surplus inventory. Confirm current availability, condition, and any test documentation directly with your supplier before placing an order.Q: Can I substitute the 115V version (P1I-1NB) for this 230V unit?
No — not without modifying your supply circuit. The P1I-1NB requires 115 VAC while the P1U-1NB requires 230–250 VAC. Swapping them without changing the supply voltage will either leave the relay unpowered or destroy it. Stick with the correct voltage variant for your circuit.Q: What does the “2U” suffix mean in the part number?
The suffix typically indicates a packaging or revision variant within the Pilz product line. Without the specific OEM datasheet for this suffix, I can’t confirm the exact distinction. If you’re cross-referencing against another P1U variant, compare the full part numbers and verify mechanical dimensions and terminal layouts match your installation.Q: How do I know if this relay has failed?
If the safety output stays open when the monitored circuit is healthy, or stays closed when it should trip, the relay is likely faulty. You can bench-test it by applying rated voltage and simulating an out-of-range condition. If it doesn’t respond correctly, replace it. Don’t try to repair a safety relay — the internal forced-guided contact architecture requires factory-level testing to certify.Q: Does this relay have a forced-guided contact structure?
Pilz safety relays are built with forced-guided (positively guided) contacts as a core safety feature — this ensures that if one contact welds shut, the complementary contact cannot close, making the fault detectable. Verify the specific contact configuration for the P1U-1NB in the OEM datasheet, but this is standard Pilz safety relay design.Q: Can I use this relay in a SIL-rated safety function?
Pilz safety relays are generally designed to meet EN ISO 13849-1 and IEC 62061 requirements. However, the specific Performance Level (PL) and Safety Integrity Level (SIL) rating for the P1U-1NB depends on how it’s integrated into the overall safety architecture. Check the OEM documentation for the certified PL/SIL rating of this specific model before relying on it in a safety function.
