In electronic control systems and industrial equipment design, push button switches are fundamental components for human–machine interaction and circuit control. The number of terminals and the internal contact arrangement directly determine wiring methods, control logic, and application scenarios.
To help engineers and procurement professionals make informed decisions, this guide outlines six mainstream terminal and contact configurations commonly found in the market, clearly explaining how normally open (NO), normally closed (NC), and common (COM) terminals are arranged and used.
1. Two-Terminal Basic Type: Single NO or Single NC
The two-terminal switch is the most streamlined configuration, featuring only two terminals and a single contact set. It is available in:
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Normally Open (NO): Open in the resting state, closes when pressed
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Normally Closed (NC): Closed in the resting state, opens when pressed
With low cost and simple installation, this type is widely used for basic lighting control, simple triggering functions, and single-circuit on/off applications.
2.Three-Terminal Changeover Type: Common with NO and NC
The three-terminal switch uses a single-pole double-throw (SPDT) design. It consists of:
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One Common (COM) terminal
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One Normally Open (NO) contact
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One Normally Closed (NC) contact
The common terminal serves as the signal input, and pressing the button switches the connection between the NO and NC circuits. Compared to a two-terminal switch, it allows signal redirection and state switching, making it suitable for signal selection, mode switching, and small equipment control.
3. Four-Terminal Independent Type: Separate NO and NC Circuits
This four-terminal configuration features two completely independent contact sets:
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Two terminals form one NO circuit
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Two terminals form one NC circuit
The two circuits do not share a common terminal and operate independently. This allows separate control of two different circuits with improved electrical isolation and reduced interference. It is ideal for applications requiring simultaneous activation of two independent states.
4. Four-Terminal Dual Type: 2NO or 2NC Synchronous Control
Also using four terminals, this configuration integrates two identical contact units that operate simultaneously. It is available in:
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2NO (Double Normally Open)
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2NC (Double Normally Closed)
Both contact sets actuate at the same time, enabling two parallel circuits with identical logic to be controlled together. This type is commonly used in redundancy safety systems, dual power switching, and high-reliability start/stop controls.
5. Six-Terminal Multi-Contact Type: Dual Independent Changeover Sets
The six-terminal switch is a classic multi-circuit solution. Internally, it contains:
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Two complete changeover contact sets (2 × SPDT)
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Each set includes its own COM, NO, and NC terminals
All contact groups are electrically isolated from one another. This configuration enables two fully independent signal switching circuits within a single switch body. It is widely used in industrial control panels, machinery systems, and automotive control interfaces where complex multi-circuit control is required.
6. Compact Four-Terminal Dual-Control Type: Integrated 2NO + 2NC
The final configuration is a compact dual-control design. Within a limited housing size, it integrates:
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Two NO contacts
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Two NC contacts
This space-efficient structure delivers dual switching capability while maintaining installation flexibility. It is commonly found in home appliances, consumer electronics, automotive interior switches, and portable electronic devices where compact dimensions are critical.
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