Wiring Siemens 3TK2828-1BB40 Safety Relay to Sinumerik 802D via PP72/48

The Siemens 3TK2828-1BB40 safety relay integrates with the Sinumerik 802D CNC through the PP72/48 PROFIBUS I/O module using standard 24 V DC digital inputs. This guide covers the dual-channel wiring topology, terminal assignments, PROFIBUS address setup, and PLC logic required to monitor an E-stop or guard-door interlock and propagate the safe state to the CNC HMI, the NCK interface, and the axis-drive enable chain.

1. System Architecture

The Sinumerik 802D is an entry-level digital controller for standard turning and milling machines. Safety devices (E-stop pushbuttons, guard-door interlocks, light curtains, two-hand controls) are not wired directly to the 802D's fast safety bus because the platform does not expose one in its base configuration. Instead, each field safety device is wired to a certified safety relay whose output contacts are read by the 802D's standard PLC inputs on the PP72/48 I/O module. The PLC then enforces the safe state by clearing NCK interface signals (pulse enable, controller enable) and raising an alarm on the HMI.

The integration path is shown in the topology below.

2. Prerequisites

• Sinumerik 802D controller (article numbers 6FC5610-0BA10-0AA0 or 6FC5610-0BA11-0AA0 for turning; milling variants 6FC5610-0BB10-0AA0 / 6FC5610-0BB11-0AA0). Verify the exact article on the rating plate.
• PP72/48 I/O module (6FC5611-0BA01-0AA0). Two PP72/48 modules are supported maximum per 802D, addressed via PROFIBUS DIP switches 1-7.
• Siemens 3TK2828-1BB40 SIRIUS safety relay, screw-terminal variant, 24 V DC coil, four NO safety contacts + one NC signaling contact.
• 24 V DC PELV/SELV power supply sized for the relay coil plus the input current of the PP72/48 inputs (typically 6 mA per input at 24 V, source: Sinumerik 802D commissioning manual).
• PROFIBUS DP cable with D-sub 9-pin connector and PROFIBUS terminating resistor switched ON at the last node.
• Sinumerik 802D Toolbox commissioning DVD or current version of SinuTrain/828D commissioning tool for PLC project transfer.

3. Siemens 3TK2828-1BB40 Safety Relay Specifications

The 3TK2828-1BB40 belongs to the SIRIUS 3TK28 family of safety relays. It is designed for monitoring single- or dual-channel E-stop circuits and protective-door interlocks up to PL e / SIL 3 per ISO 13849-1 and IEC 62061. Always confirm the published rating against the latest Siemens Industry Online Support catalog page for the article number.

Confirm the values above against the current Siemens datasheet on Industry Online Support because the catalog data sheet is the binding source.

4. Sinumerik 802D PP72/48 I/O Module

The PP72/48 is the standard distributed I/O for the 802D. It communicates with the 802D over PROFIBUS DP at up to 12 Mbit/s. The 802D's PLC processes the input image exactly like a local rack input.

The PP72/48 input image is mapped by the 802D's PLC firmware. Default mapping places the first PP72/48 (PROFIBUS address 1) at I 0.0 .. I 8.7 and the second at I 9.0 .. I 17.7. The mapping shown here is the default; the actual offset is set in the 802D commissioning tool under "PLC I/O mapping" and must be verified against the project file.

5. Dual-Channel Wiring Topology

The 3TK2828-1BB40 is wired in dual-channel mode with cross-fault monitoring. The two channels are physically routed in separate cables or separated by an earthed barrier, which is required for the relay to detect a short between channels. The following diagram shows the field connections to the relay terminals.

6. Step-by-Step Wiring Procedure

1. Isolate the cabinet. Open the main disconnect, lock-out, verify zero voltage on all power buses including the 24 V DC PELV rail and the PROFIBUS segment.
2. Mount the 3TK2828-1BB40 on a 35 mm DIN rail inside the cabinet, near the E-stop pushbutton and within reach of the PP72/48 input terminals. Maintain ≥ 30 mm clearance above and below for cooling.
3. Wire the supply. Connect +24 V DC PELV to terminal A1 and 0 V (functional earth reference) to terminal A2. Add a 1 A slow-blow fuse or PTC to protect the coil.
4. Wire the input circuit. Run two separate cables from the E-stop block: channel 1 from S11 through the first NC contact to S12; channel 2 from S21 through the second NC contact to S22. Tie the second end of S12 and S22 to the same +24 V reference that feeds A1 only if the E-stop block uses a single supply; otherwise follow the device's wiring diagram.
5. Wire the output contacts.
   • 13-14 to the line contactor K1 coil (drives the main spindle/axes power contactor).
   • 23-24 to PP72/48 input I0.0 on the first module (PROFIBUS address 1), input group 1, terminal X111 pin 4. Use a 24 V jumper from terminal X111 pin 1 (+24 V supply) through the contact into pin 4 (input).
   • 33-34 to PP72/48 input I0.1 (X111 pin 5).
   • 51-52 (NC signaling) optionally to I0.2 for cross-fault diagnostics.
6. Set the PROFIBUS address on the PP72/48 to a value not used by the 802D HMI panel or any other slave. Typical first PP72/48 is address 3, second is address 4. Power up and verify the PROFIBUS LED on the PP72/48 turns steady green.
7. Configure inputs in the 802D PLC project. Open the 802D Toolbox, edit the PLC program in the 802D's programming environment, and map I0.0 / I0.1 to the safety-monitoring function block. Set the input filter to 3 ms to reject contact bounce while keeping the response time within the safety distance budget.
8. Wire the drive enable chain. The 802D drives enable through the NCK interface signals DB31..DB61, DBX8.0 (pulse enable) and DBX8.1 (controller enable). When the safety relay opens, the PLC must clear both signals within one PLC cycle (≤ 40 ms) so the drives remove torque.
9. Re-apply power in sequence: 24 V DC logic supply, then 400 V main contactor, then drive enable from the 802D.

7. PLC Logic and HMI Integration

Below is a compact representation of the safety-evaluation logic. The 3TK2828-1BB40 output contacts are read into the PP72/48 inputs; the PLC computes a "safe" bit and a "fault" bit, raises an HMI alarm, and clears the NCK enable signals.

// Sinumerik 802D PLC — STL excerpt
// Inputs: I0.0 = ch1 contact closed (E-stop OK)
//         I0.1 = ch2 contact closed (E-stop OK)
//         I0.2 = signaling contact 51-52 (relay healthy, NC closed)
// Output:  Q0.0 = spindle/axis contactor K1 (must drop on E-stop)
//          M100.0 = internal "safety OK" latch
//          M100.1 = internal "cross-fault" flag

NETWORK 1   // Safety OK = ch1 AND ch2 AND signaling healthy
  A   I0.0
  A   I0.1
  A   I0.2
  =   M100.0           // safety OK

NETWORK 2   // Detect inconsistent channel states (cross-fault)
  XN   I0.0            // ch1 open
  X    I0.1            // ch2 closed  (one closed, one open → fault)
  O                   // symmetric:
  X    I0.0            // ch1 closed
  XN   I0.1            // ch2 open
  S   M100.1           // set cross-fault flag

NETWORK 3   // Hold-to-reset (manual restart interlock)
  A   M100.0
  A   I0.3             // reset pushbutton (NO, spring return)
  A   M100.2           // no cross-fault active
  S   M100.3           // safety latched
  AN  I0.0
  O   I0.1             // any channel open → release
  R   M100.3

NETWORK 4   // Drive enable / HMI alarm
  A   M100.3
  AN  M100.1           // suppress on cross-fault
  =   Q0.0             // contactor K1
  =   DB10.DBX56.1     // NCK: emergency stop active (low = OK)

NETWORK 5   // HMI alarm message (SinuTrain / HMI Advanced syntax)
  A   M100.1
  =   DB2.DBX180.0     // raise ALM 700001 "Safety cross-fault"
  AN  M100.0
  =   DB2.DBX180.1     // raise ALM 700002 "E-stop active"

8. Verification and Commissioning

After wiring and PLC download, perform the following functional tests. Record the results in the machine's acceptance protocol.

The total stop time used in the safety-distance calculation is:

S = (tA + tPLC + tdrive) × vmax + dintrusion

where tA ≤ 30 ms (relay), tPLC ≤ 40 ms (one scan), tdrive is the drive's deceleration response (read from the Sinamics/Simodrive parameter list, typically 50-150 ms), vmax is the maximum hazardous speed, and dintrusion is the reach distance into the hazard zone per ISO 13855.

9. Troubleshooting Matrix

10. Field-Proven Caveats

• The 3TK2828-1BB40 has no automatic reset by default. If your machine uses a "controlled stop / automatic restart" category per IEC 60204-1 §9.2.5.8, you must implement the start/restart interlock in the PLC and the operator panel, not by re-energising the relay coil.
• Never wire the 3TK2828 coil to a switched power source. The relay must remain energised for the full run-time of the machine; only the field input circuit (S11/S12, S21/S22) opens to drop the contacts.
• The PP72/48 input filter setting is global per group of 8 inputs. Choose a filter that meets the safety-distance budget but is robust against EMI from VFD cables routed in the same tray.
• When retrofitting an older 802D to a new safety relay, the 802D's PLC scan time on a heavily loaded project can exceed 40 ms. Profile it with the PLC cycle-time statistic before declaring the response-time budget.
• Always provide a separate ground reference for the 3TK2828 coil (terminal A2) and the PP72/48 24 V common. Sharing a high-impedance return path can cause nuisance tripping on relay dropout.

11. Standards Reference

Validate the design against the current revisions of these standards. They are cited as reference documents, not as confirmation that the wiring above meets any specific PL/SIL — the integrator must do that calculation.

• ISO 13849-1:2023 — Safety of machinery: Safety-related parts of control systems
• IEC 62061:2021 — Functional safety of safety-related control systems
• IEC 60204-1:2016 — Safety of machinery: Electrical equipment of machines
• ISO 12100:2010 — General principles for design — Risk assessment and risk reduction
• ISO 13855:2024 — Positioning of safeguards with respect to the approach speeds of parts of the human body

For background on how a safety relay monitors actuators and the safety contacts, see the Pilz safety-relay lexicon entry for a generic description of monitoring function. Always cross-check with the Siemens device manual, which is the binding source for the 3TK2828-1BB40.