Push Button Switches: Functions, Structure, Types, Symbols & Troubleshooting Guide

A Push Button Switch is a master control part in industrial automation. It sits in control cabinets, machine tools, and production lines. However, it only carries low control current below 5A. Therefore, it signals contactor coils instead of driving motors directly. This guide covers its functions, structure, types, symbols, and troubleshooting.

Five Core Functions of a Push Button Switch

Industrial buttons serve five key functions. First, they control basic start and stop. Green NO buttons self-lock the contactor coil to start a device, while red NC buttons cut power for shutdown. Second, self-reset NO buttons enable jogging for maintenance and calibration.

Third, composite buttons give forward-reverse interlock protection. They break the opposite loop first to prevent short circuits. Fourth, red mushroom emergency stops force a shutdown during faults. Finally, illuminated buttons show status, and key-lock buttons block unauthorized use. As a result, these switches fit CNC machines, PLC cabinets, elevators, and lifting gear.

Push Button Switch Structure and Working Principle

A standard 22mm button uses a five-part integrated structure. The color-coded cap is the external part: red for stop, green for start, yellow for alarm. The reset spring returns ordinary buttons automatically, while emergency stops need manual rotation.

Moreover, the moving contact switches circuit status with the button. It works with fixed NO and NC static contacts for wiring. The insulated shell adds dustproof and waterproof protection. In short, pressing compresses the spring to change contact state, and releasing restores the original state.

Main Types of Push Button Switch

Push buttons divide by contact function and structure. Functionally, NO buttons stay open and close when pressed for start and jog. In contrast, NC buttons stay conductive and open under pressure for safer stop and E-stop. Composite buttons use a break-before-make mechanism to avoid short circuits.

Structurally, the range covers self-reset flush buttons, locked mushroom E-stops, key-lock buttons, rotary switches, illuminated buttons, and waterproof models for harsh sites. You can review the full Push Button Switch range to match your environment.

Push Button Switch Symbols in Circuit Drawings

In electrical drawings, buttons use the symbol SB. Detailed marks include SB1 for start, SB2 for stop, and SB0 for emergency stop. Technicians read functions through symbols and colors: green SB means start loops, red means stop and E-stop, and composite symbols show the break-before-make design. By using this coding, wiring mistakes drop sharply.

How to Test a Push Button Switch with a Multimeter

Multimeter testing is the most reliable fault check, but always work power-off. Using the buzzer gear, a good NO button shows infinite resistance at rest and near-zero when pressed. A standard NC button conducts at rest and opens under pressure.

For composite buttons, verify the strict break-before-make order; simultaneous conduction means the part is scrap. In addition, visual checks catch cracked shells, black oxidized contacts, poor rebound, and burned terminals. Consequently, you can replace defective units before they cause downtime.

Conclusion

Correct use and maintenance keep industrial systems stable. Never link buttons straight to high-power loads, use NC for safety stops, and pick waterproof or reinforced types by environment. With the right checks, automated equipment runs safely and efficiently.

FAQ

Q1: Can a push button switch drive a motor directly?
No. It carries under 5A control current and only signals the contactor coil, which in turn switches the motor load.

Q2: What does the SB symbol mean in a circuit diagram?
SB is the standard push button symbol. SB1 marks start, SB2 marks stop, and SB0 marks emergency stop.

Q3: How do I test a push button with a multimeter?
Use the buzzer gear power-off. A good NO button reads infinite at rest and near-zero pressed; a good NC reads the opposite.