VFD Diagram

VFD Diagram — interactive diagram. Open it in the editor to customise components and wiring.

This is a free printable vfd diagram: download the diagram as SVG or open it and print to paper or PDF.

A VFD diagram illustrates the system-level connections between the power supply, variable frequency drive, motor, and control devices — including speed reference, feedback, and protection wiring.

Where a VFD circuit diagram focuses on the internal power electronics, a VFD system diagram takes a wider view — showing how the drive integrates into a complete motor drive system. This perspective is critical for engineers and technicians who commission, operate, or troubleshoot drive installations.

At the system level, a VFD diagram typically shows the AC supply through an upstream isolator and MCCB (moulded case circuit breaker) or fuses, then through an optional line reactor or EMC filter, into the drive's input terminals (L1/R, L2/S, L3/T). The drive's output terminals (U, V, W) connect to the motor through the motor cable — ideally screened (shielded) for EMC compliance. An output reactor or sine-wave filter may be shown between the drive output and motor for long cable runs.

The control section of the diagram shows the analogue and digital signal connections. The most common speed reference is a 4–20 mA signal from a process controller or PLC, or a 0–10 V signal from a potentiometer. Digital inputs (DI) typically carry Run/Stop, Forward/Reverse, and preset speed select signals. A fault relay contact (normally closed) is shown wired to the PLC or motor protection circuit — it opens on any drive fault.

Vector control (field-oriented control, or FOC) is a more advanced control strategy shown on modern drive diagrams. Unlike V/f control, which regulates voltage and frequency only, vector control measures or estimates the motor's magnetic flux and torque currents independently, allowing precise torque control even at near-zero speed. Sensorless vector control does this through motor model algorithms. Closed-loop vector control adds a shaft encoder (incremental or absolute) shown on the diagram as a feedback connection to the drive's PG (pulse generator) input card.

Safe torque off (STO) is a functional safety feature now standard on most industrial drives and shown on modern diagrams. Two independent STO input channels disable the IGBT gate pulses without removing power from the drive — the motor loses torque safely without the drive tripping, and power is restored instantly when the STO signal is released. This allows integration with safety PLC systems without contactors.

Most contemporary VFD diagrams also show the communications connection: Modbus RTU (RS-485), Profibus DP, EtherNet/IP, or Profinet — allowing the PLC or SCADA system to command speed, direction, and torque limits, and to read back actual speed, current, voltage, and drive status in real time.

A Variable Frequency Drive (VFD) wiring diagram distinguishes between the power circuit and the control circuit. On the power side, three-phase input (L1, L2, L3) feeds the drive's rectifier section, and the output terminals (T1/U, T2/V, T3/W) connect to the motor; a dedicated ground terminal bonds drive chassis and motor frame. The control circuit carries low-voltage signals for run/stop commands, speed reference (typically 0–10 V or 4–20 mA), and fault outputs. Correct motor cable screening and separation of power from control wiring are essential to prevent EMI issues. Diagram your VFD motor wiring circuit free in the online editor.

How to wire vfd diagram

Draw the power supply and upstream protection Begin the diagram at the AC supply, showing the isolator (disconnector) and MCCB or fuse set rated for the drive's maximum input current. Add the line reactor in series if specified. Label all three phases and the protective earth conductor.
Show the drive enclosure and main terminals Draw the VFD as a block with input terminals (L1, L2, L3 or R, S, T), output terminals (U, V, W), DC bus terminals (P+, P- or PN), brake resistor terminals (BR or PB), and the protective earth terminal (PE). Label nominal voltage and current ratings.
Add the motor cable and motor Connect the U, V, W terminals to the motor through the specified screened cable. Show shield termination at both ends. If an output filter, sine-wave filter, or dV/dt filter is required for the cable length, insert it between the drive output and the cable. Show the motor terminal box with U1, V1, W1 and PE.
Draw the control terminal block connections On a separate section of the diagram, show the control terminal block: analogue speed reference input (AI1: 0–10 V or 4–20 mA), digital inputs (DI: Run, Stop, direction, fault reset), digital outputs (DO: Run indication, fault relay), and the common/earth references. Label each terminal with its function and electrical specification.
Add encoder or PG feedback (if vector control) For closed-loop vector control, show the encoder connected to the PG card input of the drive. Specify the encoder type (incremental, absolute), supply voltage (5 V or 24 V), and pulse count (PPR). The encoder cable must be screened and routed away from power cables.
Include STO connections and safety relay Show the STO1 and STO2 input terminals connected to the safety relay or safety PLC output. Include the STO feedback contact (if provided) wired back to the safety system for loop monitoring. Note the STO circuit is typically at 24 V DC PELV level.
Add communication network connection Show the fieldbus connection (Modbus RS-485, Profinet, EtherNet/IP, or other) with the correct termination resistor at the end of the bus segment. Label node address and baud rate settings. Include shielding and earthing notes per fieldbus standard.

Specifications

Standard input supply (industrial)	380–415 V AC, 3-phase, 50 Hz (IEC); 460 V, 60 Hz (NEMA)
Typical output frequency range	0 Hz to 300 Hz (drive dependent); typical maximum motor frequency 50–120 Hz
Speed regulation accuracy (sensorless vector)	0.5 % to 2 % of rated speed
Speed regulation accuracy (closed-loop vector)	0.01 % or better of rated speed
Analogue speed reference (standard options)	0–10 V DC or 4–20 mA current loop
STO safety integrity level	SIL 2 (IEC 62061) / PLd (EN ISO 13849-1) — typical for modern industrial drives
Maximum motor cable length (no output filter)	30 m to 100 m (varies by drive; refer to manufacturer specification)
Fieldbus options (typical modern drives)	Modbus RTU, Profibus DP, Profinet, EtherNet/IP, CANopen (option card dependent)

Safety warnings

The VFD DC bus remains at hazardous voltage for several minutes after AC supply isolation. Before opening the drive or disconnecting motor cables, isolate and lock off the upstream supply, then wait the manufacturer-specified discharge time and verify DC bus voltage is below 50 V DC with a calibrated meter.
Never perform insulation resistance tests on the motor or motor cables while connected to the VFD output — the high test voltage (500 V or 1 000 V DC) will destroy the IGBT output stage. Always disconnect the VFD from the motor cable at both ends before any megger testing.
VFD output cables carry hazardous voltages at all operational frequencies including very low frequencies. A motor turning at 1 Hz still receives line voltage on its cables — do not assume a slowly rotating or stationary motor is safe to touch.
Functional safety connections (STO) must be designed, verified, and documented by a competent functional safety engineer in accordance with IEC 62061 (SIL) or EN ISO 13849-1 (PL) as applicable to the machinery safety function.
All VFD system installations must comply with applicable standards including IEC 61800-5-1 (drive safety), IEC 61800-3 (EMC), IEC 60364, and the local electrical code. EMC compliance requires correct cable routing, shielding, and earthing as specified by the manufacturer.

Tools needed

True-RMS multimeter rated CAT III / 1 000 V minimum
Clamp meter (AC and DC, with frequency display)
Laptop with manufacturer drive commissioning software
Tachometer or stroboscope for speed verification
Network analyser or power quality meter (for harmonic assessment)
Oscilloscope with differential probes (for PWM and control signal analysis)

Common mistakes

Routing control cables (speed reference, digital I/O) in the same cable tray as power cables — the high-frequency noise from the power cables induces interference in the low-level control signals, causing erratic speed control or spurious faults.
Failing to terminate the bus shield at both ends of the motor cable, which leaves high-frequency common-mode currents circulating through the earth conductors and causing EMC emissions and bearing current damage.
Setting the minimum frequency too low (below 5 Hz) for a motor with poor low-speed cooling, causing thermal damage to the motor at sustained low-speed operation — self-cooled (TEFC) motors need external or forced ventilation for sustained low-frequency operation.
Not verifying motor insulation class before VFD connection — motors with standard Class F insulation may be stressed by the PWM voltage peaks in long cable run applications and should be specified as inverter duty (reinforced insulation) or protected by an output sine-wave filter.
Connecting a PLC digital output directly to VFD control inputs without confirming voltage compatibility — a 24 V PLC output may not be compatible with a 5 V VFD control input, and the mismatch can cause logic level errors or input damage.

Troubleshooting

Motor runs in wrong direction: Cause: Phase sequence at motor terminals is reversed; or forward/reverse command is inverted in drive parameters Fix: Swap any two of the three motor output cables at the drive (U, V, W). Alternatively, change the drive's motor rotation direction parameter. Do not swap phases at the supply input — this changes the drive's internal phase reference.
Speed does not respond to analogue reference changes: Cause: Incorrect analogue input type selected (voltage vs. current), open 4–20 mA loop, or drive is in local keypad control mode Fix: Verify the drive's analogue input configuration matches the signal type (0–10 V or 4–20 mA). For a 4–20 mA input, measure the loop current — below 4 mA indicates an open circuit. Check that the drive is set to remote (terminal) control mode, not local keypad mode.
Intermittent drive faults under varying load: Cause: Undersized drive for peak load current, loose power connection causing high resistance and voltage drop, or DC bus capacitor degradation Fix: Log the fault code and the output current at fault using the drive's event log. Compare fault current against drive rated current. Check all power terminal connections are torqued to the manufacturer's specification. Measure DC bus voltage ripple with an oscilloscope — excessive ripple indicates capacitor wear.

Frequently asked questions

What is the difference between sensorless vector control and closed-loop vector control?

Sensorless vector control estimates motor flux and torque from electrical measurements and a mathematical motor model — no physical sensor is required, and speed regulation accuracy is typically 0.5–2 % of rated speed. Closed-loop vector control adds a shaft encoder for direct speed feedback, achieving accuracy of 0.01 % or better and full torque at zero speed. The encoder feedback connection is shown on the diagram as a dedicated PG card input.

What is Safe Torque Off (STO) and how is it shown on a VFD diagram?

STO is a safety function (SIL 2 or SIL 3 capable, per IEC 62061 and EN ISO 13849-1) that disables IGBT gate pulses through two independent hardware paths, causing the motor to lose torque without removing power from the drive. On the diagram, STO appears as two dedicated input terminals (STO1 and STO2) with connections to the safety relay or safety PLC output.

Why is a screened (shielded) cable specified for VFD motor connections?

The PWM switching of VFD output IGBTs generates high-frequency common-mode noise currents that radiate from the motor cable. A screened cable with the shield terminated at both the drive's EMC earth clamp and the motor's terminal box provides a return path for these currents, preventing radiated emissions from interfering with nearby control and communication circuits and ensuring EMC compliance.

What does a 4–20 mA speed reference signal represent in a VFD system?

4–20 mA is a current loop signal where 4 mA typically represents zero speed (or minimum speed set point) and 20 mA represents maximum speed. Current loops are preferred over voltage references for long cable runs in industrial environments because they are inherently noise-immune — a noise voltage picked up in the cable changes the cable voltage but not the loop current, which is driven by a constant-current source.

Can a VFD be used to control a single-phase motor?

Standard VFDs are designed for three-phase induction motors and produce three-phase output. Single-phase induction motors have start capacitors and run capacitors whose reactance is optimised for one frequency, making them unsuitable for variable-frequency control. Permanent-capacitor single-phase motors can sometimes be driven by a three-phase VFD if the motor construction tolerates it, but this is non-standard and must be verified per the motor manufacturer's specifications.

How do you wire a VFD to a motor?

Connect the three-phase supply to the VFD input terminals (L1, L2, L3) through a suitable isolator and fusing; do not use a contactor for regular start/stop as it can damage the drive. Run screened motor cable from the drive output terminals (T1/U, T2/V, T3/W) to the motor, bonding the screen at both ends to earth. The motor's direction of rotation is changed by swapping any two output phase connections or via a parameter setting — never swap the input phases for direction change on a VFD installation.