Resolving SIMOCODE 3UF5021-3AN00-1 Manual Start Failures

Resolving SIMOCODE 3UF5021-3AN00-1 Manual Start Failures

This technical reference addresses a recurring field failure: an operator attempts to start a constant-speed motor manually by bridging SIMOCODE pro V basic-unit terminals when the upstream HMI exposes only an AUTO function and the upstream DCS routes all commands over PROFIBUS. The motor does not start; the SIMOCODE trips on a defined fault because the configured control station is not issuing the ON command. The root cause is not a wiring fault at terminals 3 and 5; it is a single-source control station configuration in the SIMOCODE parameter set. This document explains the underlying control-station architecture, identifies the parameter responsible, and walks through the engineering change required to add a second, hardwired control station so manual local start becomes a safe, supported mode of operation.

1. Problem Overview

The Motor Control Center under discussion uses fused feeders, contactors, and a SIMOCODE pro V basic unit 3UF5021-3AN00-1 per motor cubicle. The HMI presents only an AUTO mode pushbutton; there is no Manual/Hand mode available to operators. The PROFIBUS network connects each SIMOCODE to the plant DCS, and the DCS issues the ON and OFF commands. The field failure manifests as follows:

1. Maintenance personnel remove the DCS from the loop or the DCS is unavailable during commissioning.
2. The technician attempts to start the motor by applying +24 V from the internal supply (terminal 5 on the as-built drawing) to the ON input (terminal 3 on the as-built drawing) of the SIMOCODE basic unit.
3. The motor does not run. SIMOCODE raises a trip, most commonly Trip - No start possible, Contactor checkback fault, or Process image error.
4. The MCC drawer cannot be locally energized for commissioning, troubleshooting, or emergency operation without involvement from the DCS engineering team.

The expected behavior — terminal bridging starting the motor — would only occur if a hardwired control station were enabled and wired to that input. The unit is, by configuration, listening exclusively to the DCS over PROFIBUS and rejects any local command that does not originate from that source.

2. SIMOCODE pro V Basic Unit Hardware Overview

The 3UF5021 is the SIMOCODE pro V basic unit, the central component of the SIMOCODE pro motor management system. It combines protection, monitoring, and control for constant-speed motors in a single device that connects to higher-level automation via fieldbus. The -3AN00-1 suffix identifies the PROFIBUS DP variant in the standard order code block. Siemens publishes the SIMOCODE Smart Motor Management System product page with current ordering information and the link to the Industry Online Support entry for the device manual.

The basic unit performs the following functions concurrently:

• Motor protection — overload (thermal image via the connected current measuring module), phase failure, phase sequence error, stall, jam, undercurrent, overcurrent, earth fault (with the 3UL22 residual-current transformer), and thermistor (PTC) trip via dedicated input.
• Motor control — direct-on-line, reversing, star-delta, Dahlander, pole-changing, soft-starter bypass, and frequency-converter bypass (the latter requires coordination with the VFD).
• Status and diagnostics — operating hours, number of starts, last trip cause, statistical data, and process values (currents, voltages where supported, power) sent cyclically to the DCS via PROFIBUS.

The basic unit has on-board inputs and outputs that can be wired to hardwired commands and contactor control. These are the terminals the operator attempted to bridge.

3. Control Station Architecture and PROFIBUS Integration

SIMOCODE organizes all motor control commands into a maximum of four control stations. A control station is a logical source of ON, OFF, and mode-change commands. Only one control station can be active at any moment, and SIMOCODE evaluates commands exclusively from the active station. Commands arriving from inactive stations are rejected and, depending on parameterization, may raise a fault.

In the MCC described, only CS1 (PLC/DCS) is enabled in the parameter set. The Control station parameter group in the SIMOCODE parameter list contains the bits that allow or disable each station. When only CS1 is enabled:

• SIMOCODE expects the DCS to issue ON/OFF via cyclic PROFIBUS write (bit "ON" / "OFF" in the process image).
• Hardwired inputs configured for ON (terminal 3 → IN1 by default on the basic unit) are logically inert; they update the input image but do not produce an ON command.
• If a contactor is somehow energized from an external source while the DCS has not issued ON, SIMOCODE detects this via its Contactor Checkback function (feedback from a contactor auxiliary contact) and trips.
• If the motor is started via the upstream fused disconnect and contactor without SIMOCODE issuing the close command, the trip function remains armed and will fire on the next running-check violation (no-start, missing current, etc.).

The 3UF5021-3AN00-1 integrates into the PROFIBUS DP network as a slave. Each SIMOCODE occupies one PROFIBUS slot with a GSD file shipped with the device:

• DP-V0 cyclic I/O: typically 10 bytes of output data (commands from DCS: ON, OFF, reset, control-station selection) and 10 bytes of input data (status: running, tripped, current values, fault codes).
• DP-V1 diagnostic: extended diagnostic messages for trip causes and statistical data, polled acyclically by the master.

The DCS writes the ON bit to the cyclic output word. SIMOCODE processes this command only when CS1 is the active control station. With CS1 permanently enabled and no other control station configured, the field technician's terminal-bridge approach will never energize the contactor.

4. Why Hardwire Bypass Trips the System

The attempt to bridge terminal 5 (+24 V internal supply) to terminal 3 (ON input) is, in principle, the correct wiring to start the motor via a hardwired control station — but only if a control station wired to that input is the active station. In the installed configuration, the input is present but unused at the control logic level. The technical sequence that follows is:

1. 24 V is applied to terminal 3. The input debounces and SIMOCODE sees IN1 = HIGH in the process image.
2. IN1 is not mapped to a control function. The control function block for "ON command from local" requires that the active control station is CS2. CS2 is disabled (parameter "Control station CS2 enabled = FALSE").
3. No ON command is produced. The contactor output remains OFF.
4. If the contactor is closed by an external means (for example a maintenance override), the contactor checkback input reports the closed state, but SIMOCODE never issued the close command. The "Commanded / Actual" comparison flags a Contactor checkback fault.
5. Trip is raised. SIMOCODE opens the contactor via the OFF output and logs a trip event. The HMI receives the trip via PROFIBUS and shows the fault.

5. Terminal Reference for 3UF5021-3AN00-1

The basic unit provides on-board terminals that can be used for hardwired control. The following table summarizes the terminal assignments on the 3UF5021 basic unit. Verify against the wiring diagram supplied with the cubicle, as terminal numbering in the project may vary if a digital I/O module is fitted.

6. Solution: Add a Second Control Station

The engineering solution is to configure CS2 (or CS3 / CS4) as a second, hardwired control station, and select between CS1 (DCS) and CS2 (local) using a physical selector switch wired to a SIMOCODE digital input. The DCS remains the primary operator; the local control is the maintenance backup. This is the configuration Siemens documents as the standard pattern for SIMOCODE pro V MCC applications.

6.1 Required Hardware

• Two-position selector switch (Auto / Manual) rated for the cubicle environment, mounted on the door.
• Two pushbuttons (Start / Stop) for Manual mode, also on the door.
• Wiring from the selector and pushbuttons to SIMOCODE basic-unit inputs (terminals 3, 4, 5, 6 as available) or to a digital I/O module (3UF7300 / 3UF7310) if all four basic-unit inputs are already used.

6.2 Parameter Changes in SIMOCODE ES / TIA Portal

The following parameter changes must be made using SIMOCODE ES (or TIA Portal with the SIMOCODE option) and pushed to the device:

6.3 Selector Switch Wiring Logic

A single-pole, two-position selector can be wired as follows:

• Auto position (CS1): Selector contact open → IN3 = LOW → CS1 active → DCS controls.
• Manual position (CS2): Selector contact closed → IN3 = HIGH → CS2 active → Local pushbuttons control.

This logic is reversed if the SIMOCODE input is configured "active low". Verify polarity against the actual parameter setting. The selector switch must also be wired such that PROFIBUS commands from the DCS cannot start the motor when the switch is in Manual; this is enforced by SIMOCODE because CS2 is the active station and CS1 commands are ignored while CS2 is active.

7. Step-by-Step Commissioning Procedure

After making the parameter and wiring changes, perform the following verification sequence before energizing any motor.

7.1 Pre-Energization Checks

1. Confirm all cubicle wiring matches the updated as-built drawing; specifically check that terminal 5 (or whichever input carries the selector) is wired to the Auto/Manual switch and not to the internal +24 V rail directly.
2. Verify PROFIBUS termination at the device — DIP switch on the basic unit set to ON if the device is the last on the segment.
3. Confirm the 24 V DC supply to the basic unit is from a stable, separately fused source, not from the contactor coil circuit.
4. Open the upstream fused disconnect or withdraw the contactor; do not attempt any rotation test until all checks pass.
5. Verify the motor FLA setting on the current measuring module matches the motor nameplate; the overload class (5/10/15/20/25/30) must be selected per motor and application.

7.2 SIMOCODE Parameter Push

1. Connect a PC running SIMOCODE ES (or TIA Portal with the SIMOCODE option pack) to the basic unit via the system interface using the 3UF7940 cable.
2. Open the device in the project, navigate to Parameters > Control stations, and confirm CS2 is enabled.
3. Click Load to device. The device LED flashes during write; do not interrupt.
4. Click Save parameter set permanently on the device (via the menu) so the changes survive a power cycle.
5. Disconnect the PC.

7.3 Local Manual Start Verification

1. Place the cubicle selector switch in Manual.
2. Press the local Stop pushbutton; confirm SIMOCODE is in a non-tripped state (green "Ready" LED).
3. Press the local Start pushbutton briefly. The contactor should close; the green "Run" LED should illuminate; motor current should ramp on the display.
4. Press the local Stop pushbutton. The contactor should open.
5. Toggle the selector switch to Auto. The DCS should regain control.
6. From the DCS HMI, issue an ON command. The contactor should close, matching the behavior observed before the change.
7. From the DCS HMI, issue an OFF command. The contactor should open.

7.4 Fault Simulation

1. With the selector in Manual and the motor running, press the local Stop; confirm the trip-free OFF (no trip is recorded, only an OFF event).
2. With the selector in Manual and the motor running, open the cubicle door interlock or simulate a contactor-checkback failure. SIMOCODE should trip and require a manual reset via the Reset pushbutton or the DCS.
3. From the DCS, attempt to start the motor while the selector is in Manual. The DCS command must be rejected; no contactor closure should occur.

8. Verification Checklist

9. Best Practices and Field Notes

• Document the selector logic in the cubicle. Use an engraved label that reads "Auto = DCS, Manual = Local Maintenance" with a key-operated switch to prevent unauthorized mode changes.
• Use a maintained selector. Avoid momentary-contact selectors — they cannot reliably indicate the active control station if left in an intermediate position.
• Mirror CS2 status to the DCS. SIMOCODE can expose the active control station in the cyclic input word. Bring this status into the DCS so operators can see "Manual" mode is active on any cubicle.
• Never wire an input directly to +24 V without an input function. Bridging an internal supply to an input that is not mapped to a control function produces a no-op; the motor will not start and there is no benefit. The correct wiring routes through the input configuration that the SIMOCODE parameter set recognizes.
• Always save parameters to the device non-volatile memory. Without a save, the parameter changes revert after a power cycle, and the next operator will see the same fault.
• Update the GSD in the DCS engineering station. If additional status bits are exposed, regenerate the PROFIBUS slot configuration so the DCS interprets the new bytes correctly.
• Verify the contactor-checkback wiring. If a checkback input is configured, ensure the contactor auxiliary contact is wired to the correct terminal and the parameter "Contactor checkback active = TRUE" is set. An incorrect checkback configuration will raise nuisance trips.
• Distinguish trip vs. fault. SIMOCODE can be configured to differentiate "trip" (latching, requires reset) from "fault" (auto-resettable). Configure per the plant's protection philosophy.
• Use a digital I/O module for expansion. If all four on-board inputs are committed (e.g., to thermistor, external trip, two interlocks), add a 3UF7300 (4 digital inputs) or 3UF7310 (2 digital inputs / 1 output) module rather than reassigning existing safety inputs.
• Plan PROFIBUS addresses. Each SIMOCODE must have a unique PROFIBUS address between 1 and 125. Document the address plan in the MCC drawing set; addressing conflicts cause the green LED to blink without faults being logged.
• Validate against IEC 60947-4-1. The contactor selection and the overload trip class must satisfy the relevant motor and starter standard; verify against the project specification, not against this article.

10. Troubleshooting Matrix