Phoenix Contact 2963938 Safety Relay

Full Model Name: PSR-SPP24UC/ESA4/2X1/1X2

Series: PSRclassic safety relay, Phoenix Contact dual-channel safety monitoring module for emergency stop and safety gate monitoring

✅ Core Safety Ratings

EN ISO 13849: Cat.4 / PL e

IEC 61508 / EN 62061: SIL 3

Stop Category: Category 0 stop

✅ Electrical Specifications

Supply: 24 V DC (-15% ~ +10%), typical power consumption 1.68 W, typical current 70 mA

Output: 2 safety normally open contacts + 1 signal feedback contact

Contact rating: 250 V AC/DC, continuous current 6 A (AgSnO₂ gold-plated contacts)

Minimum switching load: 10 V, 100 mW

Mechanical life: approx. 10⁷ operations

Response time: approx. 150 ms for automatic start; release time 20~45 ms

Recovery time: ≥1 s

✅ Wiring & Construction

Wiring type: Push-in pluggable terminals

Wire cross-section: 0.2~1.5 mm² (AWG24~16), stripping length 8 mm

Mounting: DIN rail mounting, yellow housing RAL1018, PA material

Dimensions: W22.5 mm × H112 mm × D114.5 mm

Protection class: IP20 (module body)

✅ Functions & Start Mode

Dual-channel monitoring: emergency stop buttons, safety gate switches

Start mode: automatic start (ESA4 version, no external reset)

Built-in status LED indicators

Input circuit supports two-wire safety circuit detection for wire breakage and short-circuit faults

✅ Environmental Conditions

Operating temperature: -20℃ ~ +55℃

Storage/transport temperature: -40℃ ~ +70℃

Vibration: 10~150 Hz, 2 g; shock 15 g

Maximum altitude: 2000 m

✅ Selection & Alternative Reference

Comparable models in the same series:

2963941: Manual reset version (ESA2)

2963925: Single-channel simplified version

Note: ESA4 = automatic start; ESA2 = external reset required. Not directly interchangeable.

✅ Typical Applications

Machine tools, automated production lines, conveying equipment, robot peripheral safety circuits, dual-channel emergency stop / safety gate monitoring, meets PL e and SIL3 safety requirements for machinery.

Troubleshooting Checklist for PSR-SPP-24UC/ESA4/2X1/1X2 (Order No.2963938) – Field Version

(I) Fault Phenomenon + LED Status + Troubleshooting Steps

1) Power LED off after power-up (no module response)

Possible causes: No supply voltage, undervoltage, reversed polarity, loose terminals, internal burnout

Troubleshooting steps:

1. Measure voltage at A1/A2: must be 24 VDC (20.4~26.4 V), AC220V is strictly prohibited
2. Check whether wires are securely clamped in push-in terminals, stripping length 8 mm, no poor contact
3. Confirm polarity is not reversed (A1=+24V, A2=0V)
4. Power cycle; if LED still off → internal module failure, replace directly

2) Power LED on, but safety output contacts do not close (no main output)

Case A: Fault in input circuit (dual-channel emergency stop / safety gate)

1. Confirm first: this model is ESA4 automatic start, no external reset terminal, reset button is not required
2. Measure two input channels (S11/S12, S21/S22): both channels must conduct simultaneously
3. Common faults:

Broken wire on one channel, poor contact of normally open contacts

Short circuit between two signal wires (short-circuit in two-wire circuit triggers fault lockout)

Oxidized or mechanically jammed contacts of safety gate switch

4. Short-circuit test: temporarily short S11-S12 and S21-S22. If relay pulls in → external wiring / switch damaged; still no pull-in → module fault

Case B: Fault lockout triggered by circuit detection (internal latch)

Phenomenon: Input signal appears normal, but relay stays open, still inactive after power cycle

Causes: Mismatched timing of two channels, short-circuit / wire breakage stored in fault memory

Handling: Power off for ≥1 minute then re-power; remains locked → replace module

3) Relay pulls in and opens immediately after release (momentary action)

Causes: Poor contact of input circuit, loose wiring, contact bounce of button

Troubleshooting: Measure voltage drop section by section to eliminate loose terminals; use shielded cable to reduce interference

4) Output contacts close, but load does not operate

1. Measure 13/14 and 23/24 two sets of safety NO contacts: conduction resistance should be ＜0.5 Ω
2. Severe contact erosion (high resistance) → contact failure, replace module
3. Load-side short-circuit triggers safety disconnection, check external contactors and solenoid valves for short circuits

5) Random tripping and frequent false triggering (interference fault)

1. Route power cables and safety signal cables separately, minimum distance ≥30 cm
2. Add varistors on safety circuit to suppress surge voltage
3. Confirm supply is an isolated DC power supply without ground noise

(II) Quick Self-Check Procedure (follow sequence)

1. Measure power A1/A2: 24VDC normal ✅
2. Measure two input channels: both conducting ✅
3. Power off for 1 minute and re-power to clear fault lockout ✅
4. Short input terminals to verify relay pull-in ✅
5. Check continuity of output contacts ✅
6. Eliminate open circuit, short circuit and interference on external wiring ✅

(III) Prohibited Operations (to avoid invalidating safety rating)

Do not modify ESA4 automatic start model for external reset, this will invalidate PL e / Cat.4 rating

Do not parallel the two input channels; dual channels must be wired independently

Do not connect freewheeling diodes across safety contacts (reduces contact service life)

1. Full Model List of PSR-SPP-24UC Series (Order No. + Model + Start Mode + Contact Configuration)

(1) Dual-channel master modules for emergency stop / safety gate (ESA series, Cat.4 / PL e / SIL3)

1. 2963938 | PSR-SPP-24UC/ESA4/2X1/1X2 | Automatic start (ESA4) | 2 safety NO + 1 feedback
2. 2963941 | PSR-SPP-24UC/ESA2/2X1/1X2 | External manual reset (ESA2) | 2 safety NO + 1 feedback
3. 2963954 | PSR-SPP-24UC/ESA2/4X1/1X2/B | Manual reset | 4 safety NO + 1 feedback (B pluggable terminal version)
4. 2963996 | PSR-SPP-24UC/ESAM4/8X1/1X2 | Automatic start | 8 safety NO contacts (high-output version)

(2) Single-channel simplified version (Cat.1~3 lower safety level)

5. 2963925 | PSR-SPP-24UC/ESA4/1X1/1X2 | Single-channel automatic start

(3) Contact expansion modules (URM, used with master module for output expansion)

6. 2964005 | PSR-SPP-24UC/URM4/5X1/2X2 | 5 NO + 1 NC expansion contacts
7. 2981046 | PSR-SPP-24UC/URM4/5X1/2X2/B | B pluggable terminal version

(4) Model Naming Rule

PSR-SPP-24UC / ESA4 / 2X1 / 1X2

24UC: 24V AC/DC universal (this series only supports DC24V in practical use)

ESA4 = automatic start; ESA2 = external reset; ESAM = high-output multi-contact

2X1: 2 safety normally open contacts; 1X2: 1 feedback contact

III. Supplementary Interchange Notes

1. 2963938 (ESA4 automatic) ≠ 2963941 (ESA2 manual reset). Wiring and PLC logic cannot be directly reused. Model replacement is mandatory to change reset mode.
2. Suffix /B = separable pluggable terminals; no /B = fixed terminals. Electrical performance identical, only terminal structure differs.

Working Principle of Phoenix Contact PSR Dual-Channel Safety Relay (2963938, PL e / Cat.4 / SIL3)

Core summary: Two independent internal monitoring circuits check safety input signals continuously, while self-testing internal faults. It prevents safety loss caused by single-point failure. Once dangerous signal, wire breakage, short circuit or internal fault is detected, safety outputs are reliably de-energized.

A standard relay only has one coil and one contact set. Single-point failure may cause contact welding and loss of protection, which is the problem safety relays are designed to solve.

1. Dual-Channel Input Principle (Core for E-Stop & Safety Gates)

For model 2963938: Channel 1 S11-S12, Channel 2 S21-S22. Two independent circuits connect to one dual-contact emergency stop or safety gate switch.

✅ Normal condition: Both channels conduct simultaneously → module confirms safe condition, safety outputs close

❌ Safety trigger (E-Stop pressed, safety gate opened): Both channels open at the same time → safety outputs cut off immediately

⚠️ Fault detection:

One channel open, one channel closed → identified as wire breakage or single contact failure → fault lockout, outputs open

Short circuit between the two channels → module detects short-circuit fault and latches off

Design goal: Avoid false safe status caused by broken wire or welded contact. This is the foundation of Cat.4: safety function remains available after a single fault.

Distinction: ESA4 (2963938 automatic start): outputs restore automatically once both channels return to conducting state; ESA2 requires an external reset button for confirmation.

2. Internal Dual-Channel Self-Test & Cross Monitoring (Key Difference from Standard Relays)

A safety relay is not simply a pair of ordinary relays. It contains two independent drive circuits plus two safety contact banks monitoring each other:

1. Contacts of the two internal relays are connected in series inside the safety output path (outputs 13/14, 23/24)
2. The module continuously compares the status of both internal relays:

If one internal relay contact welds closed, the other channel detects inconsistent status and locks the module, preventing output reclosure

Power-on self-test runs at startup to check coil and contact welding faults

👉 A standard relay with welded contacts keeps load powered. Safety relays detect this fault and lock out, preventing dangerous unintended startup.

3. Feedback Contact (1X2, auxiliary contact for 2963938)

This auxiliary contact is not used for safety disconnection, only for status feedback to PLC or indicators:

It operates synchronously when safety outputs close

PLC uses it to judge safety circuit readiness and E-stop reset status

Important: Do not use this auxiliary contact for safety stop! Safety shutdown must use the two main safety contacts.

4. Fault Latch Logic

The module enters fault lockout when any of the following occurs:

Mismatched dual-channel signals

Short circuit or wire breakage on input wiring

Internal relay contact welding fault

Timing anomaly caused by electromagnetic interference

Once locked, outputs will not restore automatically even after external wiring is repaired (ESA4 also requires sufficient power-off time to reset; ESA2 needs reset button actuation).

Design philosophy: Faults must be visible to personnel instead of silent recovery, eliminating hidden hazards.

5. Category 0 Stop (This model 2963938 is Category 0)

Safety relay outputs directly cut off the coil circuit of contactors, which is Category 0 stop: immediate power removal, coast-to-stop

Comparison:

Cat.0: Direct power cut (this model)

Cat.1: Controlled deceleration stop with delayed power removal (high-end safety controllers)

6. Safety Rating Mapping

Cat.4: Dual-channel + self-test + fault lockout, single fault will not disable safety function; multiple faults are detected as much as possible

PL e: ISO13849, extremely low probability of dangerous failure, suitable for robots, machine tools, presses and high-risk machinery

SIL3: IEC61508 functional safety, applied to high-risk process equipment

7. Simple Analogy

Standard relay: Actuate when signal received, no self-check. Welded contact keeps load energized.

Safety relay:

Two eyes (dual input channels), two hands (two safety contact sets). The two eyes watch the two hands mutually.

If one eye loses signal or one hand sticks closed, it releases power immediately and locks itself to prevent dangerous startup.

Common Misconceptions

1. ❌ Two ordinary relays wired together do not equal a safety relay: standard relays lack cross-monitoring and short/open circuit detection, cannot achieve PL e
2. ❌ Dual-channel does not mean simple parallel wiring: channels must be independent. Shorting S12 and S22 disables dual-channel fault detection