Pepperl+Fuchs WE77/Ex-2 Isolated Switch Amplifier

Pepperl+Fuchs WE77/Ex-2 Installation & Wiring Guide

WE77/Ex-2: Dual-channel NAMUR isolated switch amplifier (intrinsically safe barrier). Must be installed in safe-area control cabinet only. Blue terminals = intrinsically safe side (connect to field explosion-proof sensors). White/red terminals = non-intrinsically safe side (connect to PLC and power supply).

Product Name: Isolated Intrinsically Safe Switch Amplifier

Note: WE77/Ex-2 is an obsolete legacy model. Recommended replacement for new projects: KFA6-SR2-Ex2

1. Model Code Definition

WE77: Product family, NAMUR switch amplifier

Ex: Intrinsically safe explosion-proof design

2: Dual-channel version (WE77/Ex-1 = single-channel)

Two power supply variants:

1. WE77/Ex-2 115V: 115V AC supply
2. WE77/Ex-2 230V: 230V (220V) AC supply, most common in China
3. Core Functions

Intrinsically safe isolated barrier for NAMUR sensors and dry contact mechanical switches located in hazardous areas. It isolates and transmits binary switch signals from hazardous area to control system in safe area. Equipped with LB Lead Breakage detection, supports reverse operation mode. Each channel has independent relay change-over contact output.

Field side: Intrinsically safe circuit EEx ia IIC, suitable for Zone0/1/2 hazardous locations

Control side: Passive relay dry contact output (non-intrinsically safe)

Supported inputs: NAMUR proximity sensors (EN60947-5-6), passive mechanical contacts

3. Key Electrical Specifications

Intrinsically Safe Parameters (Field Side)

U₀: 13.5 V DC

I₀: 62 mA

P₀: 125 mW

Explosion group: IIB / IIC

Permitted external values: IIB: Co=0.929µF, Lo=5mH; IIC: Co=0.23µF, Lo=3mH

NAMUR Input

Open circuit voltage ≈8V DC, short-circuit current ≈8mA

Switching threshold: 1.2~2.1mA, hysteresis approx.0.2mA

Lead breakage detection: Fault alarm upon cable disconnection

Relay Output (1 SPDT change-over contact per channel)

Contact rating: 250V AC /4A; 24VDC/4A

Response time: Pull-in ≈10ms, Drop-out ≈20ms

Max switching frequency: ＜10Hz

Mechanical life: 10⁷ switching cycles

Power Supply

230V version: 198~253V AC, 45~65Hz; Power dissipation approx.2.5W

115V version: 103.5~126V AC, 45~65Hz

4. Mechanical & Environmental Data

Dimension: 40(W) ×104(H) ×110(D) mm

Weight: approx.410g

Mounting: DIN rail clip mounting

Enclosure protection: IP20 (for cabinet installation only)

Ambient temperature: -25℃ ~ +60℃

Terminals: Screw terminals

5. Certification Information

ATEX Certificate: PTB 02 ATEX 2065 / PTB Ex-79/2043X

Explosion marking: II (1) GD [EEx ia] IIC

6. Terminal Assignment (WE77/Ex-2)

Channel1 field input: Terminal 1(-), 2(+)

Channel2 field input: Terminal 8(+), 9(-)

Channel1 relay output: 10/11/12 (change-over contact)

Channel2 relay output: 13/14/15 (change-over contact)

Power supply: 17, 18

7. Application

Chemical, pharmaceutical, oil & gas hazardous locations: Signal isolation for NAMUR proximity sensors, explosion-proof limit switches, explosion-proof level switches. Relay signals are sent to PLC/DCS DI modules.

8. Spare Parts & Replacement Notes
9. WE77/Ex-2 no longer recommended for new projects by manufacturer. Direct replacement: KFA6-SR2-Ex2 (dual-channel NAMUR safety barrier, relay output, equivalent function, smaller footprint)
10. For maintenance of existing systems: Only surplus / stock spare parts available. Confirm 115V or 230V variant before procurement, the two versions are not interchangeable.
11. Single-channel equivalent: WE77/Ex-1, replacement KFA6-SR1-Ex
12. Common Troubleshooting
13. No input response: Check for LB lead breakage alarm on NAMUR loop; verify external capacitance/inductance does not exceed intrinsic safety limits
14. Relay fails to switch: Confirm power supply variant matches device rating; verify input current falls within NAMUR operating range
15. Frequent false lead breakage alarm: Excessive cable length with high distributed capacitance/inductance, or damaged cable insulation
16. Mechanical Installation
17. DIN Rail: Standard 35mm DIN rail mounting. Hook top clip onto rail, press module down to lock. To remove: Lift bottom latch and pull outward.
18. Operating Environment

Ambient temperature: -25℃ ~ +60℃, cabinet ventilation required; keep away from heat sources, vibration and corrosive gas

Protection class IP20, indoor cabinet use only, not for open or humid direct exposure

Mounting clearance: Small gaps between adjacent modules recommended for heat dissipation

3. Mandatory Explosion Protection Rules

✅ Unit must be mounted in safe area, NEVER install in Zone0/1/2 hazardous areas

✅ Intrinsically safe cables (blue) and non-intrinsically safe cables (power, relay output) must run in separate trunking/conduits, cannot share same conduit

2. Terminal Table

Important: NAMUR field wiring is polarity sensitive. Reversed polarity will trigger LB lead breakage fault and unit malfunction.

3. Wiring Schemes

Scheme 1: NAMUR Proximity Sensor (Most Common)

Channel1: 2-wire NAMUR sensor → Terminals 1(-), 2(+)

Channel2: 2-wire NAMUR sensor → Terminals 8(+), 9(-)

NAMUR loop includes LB lead breakage monitoring: Cable break, short circuit or reversed polarity will trigger channel fault LED.

Scheme 2: Explosion-proof Passive Dry Contact (Limit Switch)

Dry contact directly connected to IS terminals, lead breakage detection remains active. No external supply for contact; WE77/Ex-2 provides approx.8V/8mA IS drive internally.

Relay Output Wiring (to PLC DI)

Each channel is SPDT passive change-over contact, no external supply required

Channel1: 11 Common, 12 NO, 10 NC

Channel2: 14 Common, 15 NO, 13 NC

Contact maximum rating: 250V AC / 4A; 24VDC /4A. Do not overload to avoid contact burnout.

Power Wiring

Terminals 17 & 18 for AC supply:

WE77/Ex-2 230V version: AC 198~253V (Mainland China standard)

WE77/Ex-2 115V version: AC 103.5~126V

⚠️ Hardware differs between two power versions, NOT interchangeable.

4. Cable Selection (Explosion Compliance Mandatory)
5. Intrinsically safe side (Blue terminals to field instrument): Blue IS cable recommended, conductor cross-section ≥0.5mm², rated voltage ≥500V
6. Intrinsically safe loop must be verified for maximum permitted cable capacitance Co and inductance Lo:

IIC application: Co ≤0.23µF, Lo ≤3mH

IIB application: Co ≤0.929µF, Lo ≤5mH

Excessive cable length causes distributed capacitance/inductance over-limit, invalidating intrinsic safety certification.

3. Shielded cable: Shield single-point earthed at control room end, shield floating at hazardous area side to prevent earth loop current.
4. Wiring Procedure (Safety Sequence)
5. Power off! Isolate all power sources and confirm zero voltage before wiring
6. Connect field intrinsically safe cables first (blue terminals), verify polarity
7. Connect relay output cables to PLC DI modules
8. Connect module power terminals 17 &18 last
9. Tighten all screw terminals, no loose strands or exposed copper causing short circuit
10. Pre-power check: IS cables separated from power cables, no mixed routing
11. Power-on commissioning: Power on without field load first and check channel LEDs. Connect field sensors, test switching action and LB fault function.
12. Commissioning & LED Indication

Independent LED per channel: Illuminated when valid input signal present; LB lead breakage fault will extinguish LED / trigger fault alarm

Operation mode: Reversible mode available (relay de-energizes when input activates), configurable per project requirement

Lead breakage test: Disconnect field sensor wire, module shall detect line fault and activate LB alarm.

7. Critical Prohibitions & Common Pitfalls
8. ❌ Megger insulation test is forbidden on intrinsically safe terminals! High voltage from megger will destroy internal IS circuit and permanently damage unit. Remove all IS wiring before any cable high voltage test.
9. ❌ Never route 220V power cables or non-IS signal wires into blue intrinsically safe terminals; intrinsic safety protection will be destroyed.
10. ❌ IS circuits and non-IS circuits cannot share same cable or trunking.
11. ❌ Do not install WE77/Ex-2 in hazardous area.
12. ❌ Do not exceed Co/Lo intrinsic safety limits, explosion certification will be invalid.
13. ❌ Do not overload relay contacts; damaged relay contacts cannot be repaired separately, full module replacement required.
14. Earthing Instruction

WE77/Ex-2 is transformer-isolated safety barrier; galvanic isolation between IS side and control side. Module housing connected to cabinet protective earth as standard, earth resistance ≤4Ω. Isolated barrier does NOT require dedicated intrinsic safety earth like zener barriers.

9. Post Power-On Quick Fault Diagnosis
10. No LED illumination after power-up: Check voltage at terminal 17/18, confirm 115V/230V model match, check loose power terminals.
11. Persistent LB fault alarm: ①NAMUR polarity reversed; ②broken cable; ③cable distributed capacitance/inductance over-limit; ④field sensor damaged.
12. Sensor switches but relay does not toggle: Verify NAMUR current within operating range; check NO/NC contact selection.
13. Unintended relay chattering/false switching: Power fluctuation, electromagnetic interference. Use shielded cable and separate strong/weak signal wiring.

WE77/Ex-2 Intrinsically Safe Blue Terminals & Non-Intrinsically Safe Relay Terminal Current Parameters

Distinguish between intrinsic safety certified maximum short-circuit current Io (explosion parameter) and NAMUR normal operating current. Non-intrinsically safe side is relay contact rated current.

🔵 Blue Terminals: Intrinsically Safe Field Input Side

WE77/Ex-2 230V version (Mainland China mainstream)

1. Intrinsic safety maximum short-circuit current Io = 62mA (certified explosion parameter. In short-circuit condition, module limits output current below this value to maintain explosion safety)
2. NAMUR normal operating current: Open circuit ≈8V DC, static short-circuit current ≈8mA; Switching threshold 1.2~2.1mA per NAMUR standard

Note for 115V WE77/Ex-2 variant: Io=31mA. Always confirm power supply version during selection.

⚠️ Important: 62mA is the safety limit short-circuit current, NOT normal working current. Under normal NAMUR sensor operation, loop current is only a few milliamps.

⚪ White Terminals: Non-intrinsically Safe Relay Output (Terminals 10/11/12,13/14/15)

SPDT change-over contact rated load current (resistive load) per channel

AC 250V: 4A (cosφ>0.7)

DC 24V: 4A

DC 60V: 0.6A

DC 220V: 0.1A

Max contact power rating: 500VA; Overload will cause contact erosion, module non-repairable.

Additional: Module Power Terminals (17,18)

Total power dissipation approx.2.5W. For 230V AC supply, power loop current is low, approx.0.01A.

Summary Table