Reversing Starter Wiring — Step-by-Step Guide & Transcript

How to Wire a Reversing Magnetic Starter with Two Contactors

0h 09m video Published Apr 8, 2014 Transcribed Sep 6, 2026 Сергей Сощенко

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Intermediate 5 min read For: Electricians, electrical engineering students, and hobbyists with basic knowledge of contactors and motor control circuits.

AI Trust Score 70/100

⚠️ Average / Some Fluff

"Delivers a clear, practical explanation of the reversing starter circuit, though the title is generic and the content is standard educational material."

AI Summary

This video explains how to wire a reversing magnetic starter circuit using two contactors, focusing on both the control and power circuits. The presenter demonstrates the schematic, explains the interlock protection, and shows how swapping two phases reverses the motor direction.

Chapters

1 Introduction and Wiring Overview 00:01 2 Control Circuit and Interlock 01:24 3 Full Circuit Demonstration 03:09 4 Power Circuit and Reversal 06:16

[00:01]

Introduction to Reversing Starter

The video covers the reversing connection scheme for a magnetic starter, using two contactors to control motor direction.

[00:13]

Simplified Wiring for Explanation

The wiring is arranged for clarity, not as in real installations where buttons and contactors are often in different locations.

[01:24]

Control Circuit Wiring

Phase goes to STOP button, then to PUSH button. Parallel to PUSH is the block contact (seal-in). From PUSH, wire goes to the normally closed contact of the other contactor before feeding the coil.

[01:56]

Interlock Protection

The normally closed contact of the other contactor provides 'fool protection' (interlock), preventing both contactors from being energized simultaneously.

[02:53]

Coils in Parallel

The coils of both contactors are connected in parallel to the neutral (0) wire.

[03:22]

Full Circuit Operation

The presenter demonstrates the complete circuit: pressing one button energizes its contactor; pressing the other button does nothing until the first is stopped, due to the interlock.

[06:16]

Power Circuit for Reversal

To reverse the motor, any two phases are swapped. The power circuit uses the second contactor to swap phases B and C, while phase A remains unchanged.

[07:12]

Motor Connection

Three phases (A, B, C) feed contactor KM1, then to the motor. When KM1 closes, the motor runs in one direction. When KM2 closes, phases B and C are swapped, reversing the motor.

The reversing starter uses two contactors with an electrical interlock to prevent simultaneous activation, and swaps two phases in the power circuit to reverse the motor direction.

Tutorial Checklist

1 01:24 Connect phase to the STOP button, then from STOP to the PUSH button.

2 01:37 From PUSH, connect a wire to the normally closed (NC) contact of the other contactor.

3 01:56 From the NC contact output, feed the coil of the magnetic starter.

4 02:53 Connect the coils of both contactors in parallel to the neutral (0) wire.

5 06:16 In the power circuit, connect phase A to the first contact of both contactors, phase B to the second contact of KM1 and the third contact of KM2, and phase C to the third contact of KM1 and the second contact of KM2.

Study Flashcards (5)

What is the purpose of the normally closed contact of the other contactor in the control circuit?

medium Click to reveal answer

It provides interlock protection (fool protection) to prevent both contactors from being energized at the same time.