The numbers 30, 85, 86, and 87 represent a standardized terminal numbering system defined by the DIN 72552 standard, originally developed for automotive applications but now widely adopted in various industrial settings. These terminal designations create a universal language for relay connections, allowing engineers and technicians across different industries to correctly identify and wire relay components.
This standardization is particularly important as relays serve as critical switching elements in control circuits. The terminal numbers don't indicate the physical arrangement of pins but rather their functional purposes within the relay circuitry. For industrial engineers working with control systems, recognizing these designations significantly reduces the risk of miswiring and subsequent system failures.
Each numbered terminal on a relay has a specific function that determines how the relay operates within a circuit. Understanding these functions is crucial for proper implementation in industrial control systems.
| Terminal Number | Function | Circuit Role |
|---|---|---|
| 30 | Common Output | The shared connection point for the relay's switching circuit |
| 85 | Coil Negative/Ground | Provides the ground reference for the relay coil |
| 86 | Coil Positive/Power | Connects to power source to energize the relay coil |
| 87 | Normally Open Output | Connects to terminal 30 when the relay is activated |
| 87a | Normally Closed Output (when present) | Connected to terminal 30 when the relay is de-energized |
When voltage is applied across terminals 85 and 86, the relay coil energizes, creating a magnetic field that changes the internal switch position. This action connects terminal 30 (common) to terminal 87 (normally open), completing the switched circuit. When power is removed from the coil, the relay returns to its resting state, breaking the connection between terminals 30 and 87.
In more complex relay configurations, additional terminals may be present, such as 87a (normally closed contact) which is connected to terminal 30 when the relay is not energized.
Electromechanical relays (EMRs) and solid-state relays (SSRs) differ significantly in their physical operation, which affects their terminal numbering approaches. While EMRs strictly follow the 30, 85, 86, 87 convention, solid-state relays often use different terminal identification methods.
| Aspect | Electromechanical Relays | Solid-State Relays |
|---|---|---|
| Terminal Numbering | Standard DIN 72552 (30, 85, 86, 87) | Often simplified to input/output designations |
| Physical Components | Mechanical contacts, coil, armature | Semiconductor switching elements, no moving parts |
| Connection Method | Physical pin arrangement in socket | Various formats including terminal blocks |
| Identification Method | Pin numbers stamped on housing | Clear input/output labeling |
Understanding relay terminal numbering is crucial for industrial applications because it directly impacts system reliability, maintenance efficiency, and overall operational continuity. Proper terminal identification prevents costly errors that can cascade throughout automated systems.
For industrial engineers, correctly interpreting relay terminal designations provides several critical advantages:
With industrial systems becoming increasingly complex, understanding component standards like relay terminal numbering becomes a foundational skill. This knowledge allows engineers to confidently implement high-reliability components like our solid-state relays while minimizing integration challenges.
Understanding relay terminal numbering is essential for industrial automation reliability. The standardized 30-85-86-87 designation system provides a universal framework that transcends language barriers and technical backgrounds, creating consistency across industrial control applications.
Key points to remember include:
If you are looking for high quality relays for your applications, find your nearest Delcon distributor.