ATV320 Shows RDY, nSt or STO but the Motor Will Not Run: What Each State Means

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An ATV320 can have power, respond to the PLC and show no hardware fault while the motor remains stopped. The display helps explain why: RDY means the drive is waiting for a run command, nSt indicates a freewheel-stop state, and STO means Safe Torque Off is active.

These states lead to different investigations. Repeated resets will not supply a missing command, release an active stop condition or restore a safety circuit. Schneider Electric: ATV320 has no motor output

Before changing anything, photograph the display and save the drive configuration. Note whether the symptom began after a power interruption, an emergency stop, a PLC download or a drive replacement. That timing often explains more than the code alone.

RDY, nSt and STO at a glance

Display	Meaning	First question to answer
RDY / rdY	Drive ready; waiting for a run command	Is the command reaching the source the drive currently accepts?
nSt	Freewheel-stop state	Which stop condition or control-sequence requirement is holding the drive?
STO	Safe Torque Off active	Why is the configured safety circuit withholding torque permission?

This table covers three operating states, not the complete ATV320 fault list. If a separate fault code appears, record it and use its specific diagnostic procedure.

RDY: follow the run command to the drive

When RDY stays on the display after someone presses Start, begin with the command path.

The Start button may operate a PLC bit without producing a command at the drive. A permissive could be missing, the machine could still be in Manual mode, or the drive could be listening to a different command channel.

Speed reference and run command also need separate attention. Schneider documents ATV320 configurations in which Modbus supplies the speed reference while terminals supply Start/Stop. Receiving one does not prove that the other is present. Schneider Electric: separate speed reference and terminal commands

For an existing machine, compare the actual configuration with its approved control description:

Where should Start/Stop originate in the selected operating mode?
Where should the speed reference originate?
Does the drive’s monitored input or communication state agree with the PLC’s intended output?

Read the existing settings before altering them. A change that makes the keypad start the motor may simply move control away from the PLC.

Illustrative example: The PLC sends a valid speed reference over Modbus, but the drive is configured to receive Start/Stop from terminals. Increasing the speed value will not replace the missing terminal command.

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nSt: find what is requesting the stop

Schneider identifies nSt as a status rather than a fault. Several control conditions can produce it, so the wiring and selected control mode matter. Schneider Electric: nSt at power-up

The run signal was already present at power-up

With two-wire transition control, a maintained run signal present during power-up can leave the drive at nSt. The drive is waiting for the required command transition.

Under the machine’s approved restart procedure, remove the run request through the normal controls and observe the state before issuing a deliberate new start.

Changing tCt from transition to level control changes restart behaviour. It should not be used merely to make nSt disappear; the machine’s intended response to restored power must remain safe.

A stop input is open or inactive

In three-wire control, the stop input must be in its permissive state before a start can be accepted. An input assigned to freewheel stop can also hold the drive at nSt.

Compare the input assignment with the machine drawing and monitored input state. A PLC program showing “Start = TRUE” does not establish that the stop circuit is satisfied. Investigate the contact, wiring or control condition responsible rather than bridging the input.

The network is connected, but the drive is not enabled

For communication control using a sequential drive profile, successful data exchange does not necessarily mean the operating-state sequence is complete. Schneider’s ATV320 guidance specifically identifies an incomplete DriveCom command sequence as a possible reason for nSt.

Read the drive status alongside the controller’s command word. Use the sequence for the configured profile; do not copy a command-word value from a different machine or an I/O-profile example.

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STO: investigate the safety circuit

STO disables torque production. It can therefore be the expected result of an emergency-stop or guard circuit operating correctly.

Start with the machine’s safety diagnostics and approved schematic. Determine which device requested the stop, whether its reset conditions are satisfied and whether the installed safety configuration matches the drawing. Qualified personnel should investigate unexpected input conditions and wiring discrepancies.

Do not add a jumper to clear STO on an installed machine. That can defeat the safety function whose operation the display is reporting.

STO also leaves the drive’s mains and DC-bus voltages present. Electrical work still requires the specified isolation and verification procedure. A vertical or externally driven load may need independent restraint because removal of motor torque does not guarantee standstill. ATV320 Safety Functions Manual, pages 24–25

Restoring safety permission and starting production are separate actions. For an emergency-stop application, resetting the emergency stop must permit a restart without itself restarting the machine.

Use the monitor values to locate the remaining problem

Once the stop and safety conditions are understood, compare the requested speed with the drive’s reported output.

Schneider recommends these ATV320 monitor values:

Monitor	What it shows
`FrH`	Frequency reference
`rFr`	Output frequency
`LCr`	Motor current
`uoP`	Motor voltage

They are available through the monitoring menus, including the motor-monitoring submenu for the relevant motor values.

Use them as evidence, not as a component verdict:

The intended reference never appears: trace the selected reference source and its configuration.
The reference appears, but the drive remains stopped: continue investigating command acceptance, stop conditions and safety status.
The drive reports output, but the shaft remains stationary: the investigation must extend to the motor circuit, brake and mechanical load.

The last condition requires qualified electrical and mechanical diagnosis. A reported output value alone neither proves that power reaches the motor correctly nor establishes that the drive needs replacing.

Avoid changing the control profile, input assignments and speed settings together. One change at a time preserves the link between the symptom and its cause.

Frequently Asked Questions

Why does STO disappear but nSt remain?

Removing the STO condition does not satisfy every other operating requirement. A freewheel-stop input, an incomplete communication sequence or the need for a fresh run-command transition may still hold the drive. Investigate the new state rather than assuming the safety circuit has failed again.

Does terminal-triggered STO require a power cycle to reset?

Schneider states that terminal-triggered STO does not itself require a power cycle. The state can clear when the triggering terminal condition is restored through the intended circuit. Separate faults and the machine’s restart requirements still need their own handling.

The PLC is sending a speed value. Why will the drive not start?

The speed-reference channel may be working while the command channel is not. In a configuration with Modbus reference and terminal Start/Stop, a valid network speed value cannot replace the terminal run command. Verify both paths and the selected control profile.

Why did nSt appear after changing from two-wire to three-wire control?

The meaning of the inputs changes. Schneider’s documented three-wire arrangement uses the first logic input for Stop, with subsequent inputs for forward and reverse start. Existing wiring may therefore no longer satisfy the new control arrangement. Compare the wiring and assignments before attempting another start.

Can the HMI’s STO indication prove that the machine is safe to access?

No. It provides diagnostic information, not proof of electrical isolation or a secured load. Schneider also states that the safety-status registers are not approved for safety-related use. Follow the machine’s validated access and isolation procedure.

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What counts as a completed repair?

A successful repair restores the machine’s intended control sequence.

During controlled commissioning, verify the selected operating mode, deliberate start, expected direction and speed, and normal stop. Where the work affects the safety system, complete the applicable safety validation before returning the machine to service.

Keep the original configuration and a record of the final changes. If the fault began after a replacement, compare both ordinary control settings and the safety configuration rather than assuming that a similar part number means an identical setup.

RDY, nSt or STO alone is insufficient evidence for purchasing another drive. If a separate hardware diagnosis justifies replacement, a Kwoco enquiry should include the full ATV320 reference, supply voltage, motor rating and installed communication option. Include the configuration requirements as well—the replacement has to fit the control system, not just the cabinet.

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ATV320 Shows RDY, nSt or STO but the Motor Will Not Run: What Each State Means

Table of Contents

RDY, nSt and STO at a glance