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Educational use: ElectraCore supports learning and preliminary checks. It does not replace a competent electrician or engineer. Verify results, equipment data, and current local regulations before installation or live work.
Courses/Industrial Control & PLCs/Control Circuit Diagrams

lesson · 8min · Lesson 14 of 30

Forward-reverse motor control

Course syllabusCourse overview
01Motor Starters
  1. ReadDOL starter: main and control circuit
  2. ReadStar-delta starter: wiring and timer
  3. ReadSoft starters: operation and parameters
  4. ReadVariable speed drives: inverter drives
  5. quizMotor starter quiz
02Contactors & Overloads
  1. ReadContactor construction and ratings
  2. ReadAuxiliary contacts and interlocking
  3. ReadThermal overload relays: setting the dial
  4. ReadElectronic overloads and motor protection relays
  5. exerciseContactor circuit problems
03Control Circuit Diagrams
  1. ReadIEC 60617 symbols: reading control diagrams
  2. ReadLadder diagrams: European and American styles
  3. ReadDrawing a full DOL control circuit
  4. ReadForward-reverse motor control
  5. exerciseDiagram reading exercises
04Safety Systems
  1. ReadEmergency stop requirements: IEC 60204
  2. ReadSafety relays and safety PLCs
  3. ReadLight curtains and safety interlocks
  4. ReadSafe isolation: EAWR and multi-energy control
  5. quizSafety systems quiz
05PLC Fundamentals
  1. ReadWhat is a PLC and where is it used?
  2. ReadPLC architecture: CPU, I/O modules, power
  3. ReadLadder logic basics: contacts and coils
  4. ReadTimers and counters in ladder logic
  5. exerciseWriting a simple motor control program
06Panel Layout & Installation
  1. ReadPanel design: layout and component spacing
  2. ReadCable management inside panels
  3. ReadLabelling, ferrules, and documentation
  4. ReadPanel testing and commissioning checklist
  5. quizFinal assessment
Lesson · 8min
DOL STARTER · CONTROL CIRCUITLNSTOPOL NCSTART NOKM1KM1 aux NO (seal-in)3~control rung shown; power poles and motor protection are separate
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In this lesson

PurposeCore theoryWorked exampleKnowledge checkSources

In this lesson

PurposeCore theoryWorked exampleKnowledge checkSources
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ElectraCore lesson handout

Forward-reverse motor control

Industrial Control · Lesson 14 · Advanced

AdvancedReview: professional review pending

Purpose

Design forward-reverse control with phase-sequence power switching, command logic and fault-tolerant interlocking.

Before you beginMotor starter circuits · Machine hazard and protection fundamentals

Learning objectives

  • Read state and cross-references
  • Separate standard control from safety functions
  • Analyse faults and reset behavior
  • Validate the complete input-logic-output path

Reversing a three-phase motor typically swaps two phases through opposing contactors. Simultaneous closure can create a severe phase-to-phase fault and must be prevented by design.

CONTROL DIAGRAM STATE AND INTERLOCKSCONTROL DIAGRAM STATE AND INTERLOCKSSUPPLYSTARTERmotor · loadshort circuit · overload · command · interlock · isolation

Core theory

Use correctly rated forward/reverse power contactors and a verified phase sequence. Provide electrical cross-interlocks and suitable mechanical interlock; analyze welded-main and auxiliary failures.

Define whether direction change requires stop and delay, or controlled plugging/jogging duty. Select utilization category and braking/drive method for the actual mechanical process.

End-position switches and PLC commands may be operational controls; safety limit functions need the required architecture, diagnostics and validation.

Terms, symbols, and units
TermMeaningSymbolUnit
Reversing contactorOne of a pair arranging opposite motor phase sequenceNot applicableNot applicable
PluggingElectrical braking/reversal by applying opposing phase sequenceNot applicableNot applicable
Cross-interlockEach direction inhibits the opposing commandNot applicableNot applicable
Worked exampleForward is running when an operator presses reverse in a stop-before-reverse design.

Assumptions: Symbols and terminal designations are defined by the supplied drawing set; Required safety performance comes from the machine risk assessment.

  1. Drop: Forward contactor must release.
  2. Verify/delay: The design prevents reverse pickup until forward is open and required deceleration time has passed.
  3. Energize: Reverse may then close if all permissives and safety conditions remain valid.

A direct simultaneous change is rejected; the specified stop/release/delay sequence must complete first.

Reasonableness check: The conclusion is checked across normal, demand, fault, reset and restart states rather than inferred from one component label.

Common mistakes
  • Reading a contact in the energized instead of defined normal state
  • Using an ordinary PLC bit as an unvalidated safety function
  • Assuming emergency stop isolates every energy source

Where this appears in practice

Clear diagrams and validated safety functions let competent people build, test, diagnose and modify machinery without losing the intended protective behavior.

SafetyDo not bypass guards, light curtains, interlocks or safety outputs for production or diagnosis. Control hazardous electrical, pneumatic, hydraulic, gravitational and stored energy; isolate, lock off and prove dead using the site procedure before access.
Local code checkUse the current machine risk assessment, applicable type-C standard, IEC/BS EN 60204-1, ISO/BS EN ISO 13849-1 or IEC/BS EN 62061 design route, IEC 61496 where applicable, Electricity at Work Regulations, site lockout procedure and manufacturer validation instructions. BS 7671 Section 514 identification/notices does not by itself define or authorize the complete safe-isolation procedure.

Knowledge check

Is one PLC software interlock always enough to prevent simultaneous reversing contactors?

No. Use the engineered electrical/mechanical and safety architecture required by the fault analysis.

Answer: No. Use the engineered electrical/mechanical and safety architecture required by the fault analysis.

Practical exercise

Create a forward/reverse state machine covering simultaneous commands, welded contacts, limit actuation and power recovery.

Summary

  • A diagram is a state model plus physical cross-reference
  • Safety performance belongs to the complete function
  • Stop, emergency stop and isolation are distinct

Sources and review

  • IEC 60204-1:2016+AMD1:2021: Electrical equipment of machines: IEC; 6.1; International
  • ISO 13849-1:2023: Safety-related parts of control systems: ISO; 2023; International
  • IEC 62061:2021 with current amendments: Functional safety of machinery control systems: IEC; 2021; confirm current consolidated version; International
  • IEC 61496-1:2020: Electro-sensitive protective equipment: IEC; 2020; International
  • Electricity at Work Regulations 1989: UK Legislation; Current official text; Great Britain

Editorial review date: 2026-08-22. Professional electrical review is pending.

Educational material for learning and preliminary checks. Verify current local requirements and exact equipment instructions. This lesson does not replace competent professional work.

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