Wiring Tutor

All 51 wiring + fault-finding lessons

32 panel-wiring fundamentals and 19 fault-diagnosis scenarios. Each lesson runs in your browser with a virtual multimeter, drag-route wiring, and per-connection grading.

Wiring fundamentals

32 lessons covering panel layout, sensors, motors, safety, and communications.

Free

Wiring 1A — Power the PLC

A PLC does nothing until it has power. In a control panel that power comes from a 24 VDC power supply mounted on the DIN rail, and it travels in a loop: out …

See lesson →
Free

Wiring 1 — E-Stop Control Circuit

In this lab you wire an emergency-stop control circuit: an E-stop in series with a relay coil, so pressing the E-stop drops the relay. The panel's power rail…

See lesson →
Free

Wiring 2 — NPN / PNP Sensors (Sinking & Sourcing)

Industrial 3-wire DC proximity sensors normally use this IEC colour convention (always verify the device datasheet):

See lesson →
Free

Wiring 3 — Photoeye Sensor to PLC Digital Input

A retro-reflective photoelectric sensor (photoeye) emits an infrared beam toward a fixed reflector. While the return beam reaches the receiver the output is …

See lesson →
Pro

Wiring 4 — PLC Digital Output to Contactor (via Interposing Relay)

A PLC digital output is a small-signal transistor or relay. Its current rating is typically 0.1–0.5 A — enough to drive a pilot lamp or a small sensor, b…

See lesson →
Pro

Wiring 5 — Pull-up Resistor for an NPN Open-Collector Sensor

Not all sensors push a defined voltage onto their signal wire. An NPN (open-collector) sensor contains an NPN transistor whose collector is exposed directly …

See lesson →
Pro

Wiring 6 — 2-Wire 4-20 mA Loop-Powered Analog Input

Industrial process instruments — pressure transmitters, temperature sensors, flow meters — communicate their measurements using a 4-20 mA current loop. U…

See lesson →
Pro

Wiring 7 — PLC Analog Output Driving a VFD Speed Reference

A Variable Frequency Drive (VFD) controls the speed of a 3-phase induction motor by varying the frequency and voltage of the AC power it delivers to the moto…

See lesson →
Pro

Wiring 8 — Dual-Channel E-Stop with Safety Relay (Cat 3)

EN ISO 13849-1 defines Performance Levels (PL a–e) for safety functions. Category 3 mandates single-fault tolerance: a single failure anywhere in the safet…

See lesson →
Pro

Wiring 9 — RS-485 Modbus RTU Daisy Chain with Termination

Modbus RTU communicates over RS-485 — a differential signalling standard designed for long cable runs in electrically noisy industrial environments. Instea…

See lesson →
Pro

Wiring 10 — Industrial Ethernet (EtherNet/IP) Star Topology

Traditional fieldbuses — RS-485 Modbus, PROFIBUS, DeviceNet — were designed when 9600 bps was fast and network management tools barely existed. Industria…

See lesson →
Pro

Wiring 11 — Quadrature Encoder to PLC High-Speed Counter Input

An incremental quadrature encoder produces two digital pulse trains — A and B — that are 90° out of phase with each other. Because of this phase offset,…

See lesson →
Free

Wiring 12 — Three-Wire Motor Starter

The three-wire motor starter is the most common motor control circuit in industrial automation. You will find it on conveyors, pumps, fans, and compressors e…

See lesson →
Pro

Wiring 13 — E-Stop Chain with Healthy Indicator Lamp

An emergency stop (E-stop) button is the physical switch a machine operator uses to immediately halt a dangerous machine. Pressing the mushroom-head button s…

See lesson →
Pro

Wiring 14 — VFD Run/Stop with PLC Digital Command

A Variable Frequency Drive (VFD) controls motor speed by converting fixed-frequency AC mains to variable-frequency AC output. The core insight you must take …

See lesson →
Pro

Wiring 15 — RS-485 Modbus RTU Drop

RS-485 is the physical-layer standard used by Modbus RTU — the most widely deployed fieldbus protocol in industrial automation. You will encounter it on fl…

See lesson →
Pro

Wiring 16 — Dual-Channel Safety Relay with Monitored Reset

Prerequisite: complete Wiring 13 (E-Stop Chain) first. That lab teaches the single-channel NC E-stop loop. This lab extends it to the Cat 3 / PLd safety arch…

See lesson →
Free

Wiring 17 — Protected Control Power Distribution

Build the front end of a real control panel: incoming three-phase supply, door interlocked main isolator, branch circuit breaker, 24 VDC power supply, fused …

See lesson →
Free

Wiring 18 — Dry-Contact Field Inputs

Connect three common volt-free field devices to PLC inputs: a maintained selector switch, a mechanical limit switch and a tank float switch. The devices do n…

See lesson →
Pro

Wiring 19 — PLC Relay Output to Solenoid Valve

Drive a 24 VDC pneumatic solenoid through an interposing relay. The PLC output only energises the relay coil; the relay contact switches the field load. Add …

See lesson →
Pro

Wiring 20 — Complete DOL Motor Starter

Build both halves of a direct-on-line starter: the three-phase power path through isolator, breaker, contactor and thermal overload to the motor, plus the 24…

See lesson →
Pro

Wiring 21 — Forward / Reverse Motor Starter

Wire paired forward and reverse contactors. The forward contactor preserves phase order; the reverse contactor swaps L1 and L3 before the common overload. A …

See lesson →
Pro

Wiring 22 — Three-Wire Pt100 RTD

Terminate a three-wire Pt100 resistance temperature detector on a dedicated PLC temperature input. The single A conductor lands on RTD-A; the two same-colour…

See lesson →
Pro

Wiring 23 — Thermocouple Input and Shielding

Connect a low-level thermocouple signal directly to a temperature input card with correct polarity and a single-point shield. Thermocouple extension wire mus…

See lesson →
Pro

Wiring 24 — Safety Light Curtain with Dual OSSD

Connect a Type 4 light curtain to a safety relay using two independent OSSD channels, then use a safety output contact to interrupt a contactor coil. Functio…

See lesson →
Pro

Wiring 25 — VFD Safe Torque Off and Status Feedback

Integrate a dual-channel guard switch, safety relay and VFD Safe Torque Off inputs. Add the ordinary run command and hardwired running/fault feedback to a PL…

See lesson →
Pro

Wiring 26 — IO-Link Master and Smart Sensor

Connect a three-wire IO-Link sensor to Port 1 of an IO-Link master and link the master to the PLC network. L+ and L− power the field device; C/Q carries bi…

See lesson →
Pro

Wiring 27 — Control Valve with HART Commissioning

Wire a 4–20 mA analog output to a smart valve positioner, return its position feedback to an analog input, and connect a HART communicator in parallel acro…

See lesson →
Pro

Wiring 28 — Six-Wire Load Cell and Transmitter

Terminate a six-wire strain-gauge load cell on a weighing transmitter, including excitation, millivolt signal, sense conductors and shield. Send the transmit…

See lesson →
Pro

Wiring 29 — Intrinsically Safe 4–20 mA Loop

Build an intrinsically safe analog loop across the safe-area / hazardous-area boundary. The barrier limits the electrical energy that can reach the field tra…

See lesson →
Free

Wiring 41 — Dual-Channel E-Stop into a Safety Relay

Wire the stopping path the way the Industrial Safety track describes it: a two-contact E-stop button, a safety relay that watches both contacts, a reset butt…

See lesson →
Pro

Wiring 42 — Light Curtain OSSD Pair into a Safety Relay

A light curtain guards an opening with a row of infrared beams. Instead of a mechanical contact it reports through two solid-state safety outputs, called OSS…

See lesson →

Fault-finding scenarios

19 planted-fault scenarios. Use the multimeter to trace and diagnose.

Free

Fault 1 — Photoeye Polarity Reversal

Welcome to fault-finding. From here on every lesson hands you a pre-wired panel with a problem buried in it; your job is to find the fault using the multimet…

See lesson →
Pro

Fault 2 — Relay Contact Card Swap

Symptom: the line operator reports the conveyor's safety-OK indicator never came on this morning. You walk to the panel — the PSU LED is on, the relay coil…

See lesson →
Pro

Fault 3 — Rail Short at the Terminal Block

Symptom: the line operator reports the conveyor contactor never pulled in this morning — the panel went dark on the load side. You walk over: the PSU's own…

See lesson →
Free

Fault 4 — Broken +24 V Supply Wire to the PLC

Symptom: the morning shift calls — the panel won't power up. You walk over: the PSU indicator LED is on, but the PLC base is completely dark. None of the i…

See lesson →
Pro

Fault 5 — Broken 0 V Return Wire on the Contactor Coil

Symptom: the PLC is commanding contactor KM1 to pull in — the output is on, you can hear the program asking for it — but the contactor isn't engaging. No…

See lesson →
Pro

Fault 6 — Broken Signal Wire Between Photoeye and PLC

Symptom: the line operator reports the conveyor isn't indexing — the PLC isn't reacting to the photoeye on the infeed. You walk over to the panel.

See lesson →
Pro

Fault 7 — NPN Photoeye Polarity Reversal

Symptom: the line operator reports the conveyor's box-present signal at PLC input X0 has been stuck HIGH all morning even when the conveyor is empty. You wal…

See lesson →
Pro

Fault 8 — Relay Contact Card Swap (Alarm Stuck ON)

Symptom: the night-shift operator phoned: the panel's alarm beacon and X0 input have been ON since power-up, and there's no actual alarm condition — the sa…

See lesson →
Pro

Fault 9 — Blown 24 V Control Fuse

Reported symptom: The incoming supply and PSU indicators are healthy, but the +24 V distribution rail is dead.

See lesson →
Pro

Fault 10 — High-Resistance Solenoid Terminal

Reported symptom: K1 pulls in, but YV1 chatters and measures low voltage only while energised.

See lesson →
Pro

Fault 11 — Thermal Overload Trip

Reported symptom: The control supply is healthy and Start works mechanically, but KM1 cannot energise.

See lesson →
Pro

Fault 12 — Welded Safety Output Contact

Reported symptom: The light curtain is interrupted, yet the contactor coil path remains continuous.

See lesson →
Pro

Fault 13 — Pt100 Open Compensation Lead

Reported symptom: The Pt100 channel is over-range and the input card reports a sensor-break diagnostic.

See lesson →
Pro

Fault 14 — Reversed Thermocouple Polarity

Reported symptom: The indicated temperature falls when the process heats up and rises as it cools.

See lesson →
Pro

Fault 15 — Analog Valve Feedback Drift

Reported symptom: The valve local display is at 50%, but PLC feedback is consistently 7.5% high across the range.

See lesson →
Pro

Fault 16 — RS-485 Terminator Disconnected

Reported symptom: Modbus works at low baud rate but becomes intermittent at the normal rate, especially on long cable runs.

See lesson →
Pro

Fault 17 — VFD STO Channel 1 Open

Reported symptom: The guard is closed and the safety relay resets, but the VFD remains in STO active / inhibit.

See lesson →
Pro

Fault 18 — Intermittent IO-Link C/Q Conductor

Reported symptom: The IO-Link sensor stays powered but repeatedly drops to COMLOST when the machine vibrates.

See lesson →
Pro

Fault 19 — Load Cell Signal Pair Reversed

Reported symptom: The weighing value moves negative when test weight is applied, while excitation and zero stability are normal.

See lesson →

Ready to wire your first panel?

10 foundation wiring labs are Free; advanced and fault-diagnosis labs are Pro.

Sign up free →

Competency and practice field guide

PLC wiring lesson pathway: practice plan

Direct answer

The learner can select the next wiring lesson by competency and retain a signal-path explanation and measurements instead of only a completed screen.

Written for electrical and automation learners choosing a sequence from dry contacts and digital sensors to analog loops, encoders and actuator interfaces.

a technician tracing realistic industrial sensors, signal wiring, PLC inputs and measured trends at an instrumentation learning bench while studying progressive PLC, sensor, motor and instrumentation wiring practice
System map / 02

NODE 01observable

Scope

Learner prerequisites, control voltage, schematics, terminal conventions, digital inputs, outputs, relays, sensors, analog signals, encoders, motors, instruments and assessment order.

NODE 02observable

Signal path

Physical condition through device and conductor to terminal, PLC channel, tag, logic response, output interface and independent equipment result.

NODE 03observable

Baseline practice

One digital and one analog circuit assembled from a clean state and verified at named points.

NODE 04observable

Edge cases

Open wire, short, reversed polarity, wrong common, failed device, scaling error, noise, output overload and power return.

NODE 05observable

Fault practice

A schematic-reading, component, terminal, supply, conductor, I/O, interface, scaling or evidence gap.

NODE 06observable

Transfer to the job

The virtual circuit redrawn and then wired and measured under qualified supervision.

Answer surface / 07

What PLC wiring lesson should a beginner start with?

Begin with supply and common, a dry-contact digital input and a relay output before adding three-wire sensors, analog loops, encoders and motor interfaces.

How do I know a virtual wiring lesson is complete?

Explain the full signal and return path, predict named measurements, pass a changed fault case and state what remains unproven physically.