Phoenix ST series spring cage terminal block

Phoenix Contact ST Series Spring Cage Terminal Blocks: Comprehensive Analysis and Application Guide

In the fields of modern industrial automation and electrical engineering, the quality of wiring inside control cabinets directly affects the stability, safety, and maintenance efficiency of the entire system. As a leader in connectivity technology, Phoenix Contact has launched the ST series Spring cage terminal block in the CLIPLINE complete system, which has become one of the preferred solutions for engineers worldwide due to its excellent seismic performance, fast wiring experience, and long-term stable connection reliability. This article will provide a comprehensive and in-depth technical analysis of the ST series terminals, from core technology, product line architecture to specific application selection, presenting you with a detailed technical guide.

Core Technology: Advantages of Spring Cage Connection

The core of the ST series lies in its innovative spring cage connection technology. Unlike traditional screw crimping methods, it uses high endurance stainless steel springs as clamping elements. When operated with a standard screwdriver, the terminal point is opened and the wire can be easily inserted into the clamping space; After removing the screwdriver, the spring automatically resets and provides a constant, high-strength contact force.

This design brings several decisive advantages:

Seismic and airtight connection: High contact force ensures that the connection point will not loosen even in strong vibration environments such as rail transit and shipbuilding. At the same time, the pressure is sufficient to penetrate the oxide layer on the surface of the wire, form an airtight connection, prevent electrochemical corrosion, and ensure long-term stability.

Unprocessed wiring: All types of copper wires, up to a maximum of 35mm ², can be directly inserted and connected without any pre-treatment (such as tinning), greatly reducing installation time.

Large tolerance wiring space: Thanks to the optimized clamping space design, convenient and reliable wiring can be achieved for wires with nominal cross-sections, whether or not cold pressed terminals are used.

Front end operation convenience: All operations are carried out on the front of the terminal, and with the help of a standard screwdriver, wiring can be easily completed even in a compact control cabinet, while maintaining a clear view.

Overview of Product Line (Classified by Section)

The ST series provides an extremely rich product matrix to adapt to various application scenarios from signal transmission to power distribution. According to the cross-section of the wire, it is mainly divided into the following levels, each level containing multiple functional terminals.

1. 1.5 mm ² series: precision signal transmission

This series is mainly used for connecting weak electrical signals inside control cabinets. Its product types include:

Straight through, multi wire, and multi-layer terminals: such as ST 1.5/S-QUATTRO (four layer bridging terminal), used to achieve multi-point potential distribution in a limited space.

Double layer terminals: such as MZFKK 1.5, can be wired separately on two layers, effectively saving installation rail space, and both layers can be bridged.

Special function terminals: including STTB 1.5 BUS for fieldbus, STTB 1.5-PV for photovoltaic applications, and models with LED indicators for quick diagnosis of signal status.

Grounding terminal: STTB 1.5-PE with yellow green casing, used for safety protection grounding.

2. 2.5 mm ² Series: Universal Control Core

This is the most widely used series and the main force for I/O connections inside PLC cabinets.

Basic straight through terminals, such as ST 2.5, are the basic units for constructing potential strips.

Multi connection point terminals: ST 2.5-TWIN (three connection points) and ST 2.5-QUATTRO (four connection points), used for star wiring or sharing the same potential.

Sensor/actuator terminals: such as the STIO 2.5 series, designed specifically for connecting on-site sensors and actuators, with some models integrating PE pins or LED status display.

Knife switches and breaking terminals: such as ST 2.5-MT and ZDMTK 2.5, can achieve circuit breaking and testing without disconnecting wires, greatly facilitating debugging and maintenance.

Fuse type terminal: provides overcurrent protection for the circuit.

Hybrid Terminal (STS Series): One side is spring connected, and the other side is screw connected, providing a perfect solution for the transition of different connection technologies.

Micro terminals (MSB series): such as MSBV 2.5, with extremely low height, especially suitable for flat control cabinets with limited depth or 15mm DIN rails.

3. 4 mm ² Series: Balancing Power and Protection

This series achieves a good balance between load-bearing capacity and space occupation.

Fuses and lever type breaking terminals: consistent in appearance, easy to layout uniformly. We offer a variety of fuse specifications ranging from 5x20mm to 6.3x32mm.

Double layer breaking terminal: such as STTBS 4, which integrates breaking function in two layers of one terminal, suitable for compact power distribution and measurement circuits.

4. 6 mm ² Series: Electric Drive and Testing

Mainly used for controlling and testing circuits of small and medium power motors.

Test disconnect terminal (STME 6): This is the star product of this series. Specially designed for the secondary circuit of current transformers, only two STME 6 terminals are needed to form a complete testing circuit. Combined with the PAI-4-FIX test adapter and SB-ME switch jumper, safe and convenient open circuit and short circuit operations of the current transformer can be achieved.

Diode terminal: such as STME 6-DIO, used for logic control or reverse voltage protection. The manual clearly states that when the diode load reaches 5A, the surface temperature can reach 140 ° C, and attention should be paid to heat dissipation and protection.

Sliding terminal (SGSK 6): The circuit can be turned on and off by sliding the slider, and multiple measuring devices or protective relays can be connected separately.

5. Series of 10 mm ² and above: Main power distribution

10 mm ² series: including straight through, multi-layer, and hybrid terminals. For example, STU 10/4X2.5, which combines a 10mm ² screw main inlet and four 2.5mm ² spring branch outlets, is very suitable as an on-site distribution box.

16 mm ² series: mainly for straight through and multi wire terminals, capable of carrying currents of up to 90A or more.

35 mm ² series: As the high current solution in the series, the straight through terminal ST 35 can carry 125A current. In addition, there is a neutral wire disconnect terminal STN 35, which is used to disconnect the neutral wire circuit without cutting off other phase lines.

Deep functional analysis: not just connectivity

The design philosophy of the ST series goes far beyond simple wire connections, it is more like a modular electrical functional platform.

1. Flexible bridging and potential allocation

Phoenix has designed a comprehensive bridging attachment system for the ST series, greatly simplifying potential distribution.

Fixed Bridge Components (FBS/FBSR): Can bridge 2 to 50 terminals at once, quickly establishing a common potential point. For example, FBS 2-3.5 is used for 1.5mm ² terminals, and FBS 2-8 is used for 6mm ² and above terminals.

Jumping bridge: By removing specific contact guides on standard bridges, a jumping bridge can be created to achieve parallel transmission of two different potentials.

Reducing bridge: allows the connection of terminals with different cross-sections, such as connecting a 10mm ² power terminal with a 2.5mm ² control terminal to form a power distribution block.

2. Testing and measurement capabilities

The ST series fully considers the testing requirements during the debugging and maintenance phases.

Universal plug-in area: On the disconnect type terminal, a universal plug-in area is provided, which can be compatible with P-FIX isolated feedthrough connectors, P-DI isolated plugs, P-CO component connectors, and P-FU fuse plugs, achieving modular combination of functions.

Standard testing interface: Supports testing plugs with a diameter of 2.3mm. At the same time, we provide testing adapters (such as PAI-4) that are compatible with 4mm diameter safety test plugs and support quick connections with all mainstream multimeters and testing instruments.

3. Visual and electrical isolation

Partition plates, such as the D-ST... series, have a contour higher than the terminal body, providing not only electrical isolation but also clear visual grouping to prevent accidental contact between circuits of different voltage levels.

Cover segments: Used to cover the unused protruding parts of three or four layer terminals. When two layers of terminals are installed side by side, it can effectively prevent fingers from touching live parts and meet the highest safety standards.

4. Hybrid Terminal: Integration of Connection Technologies

The STS and STU series hybrid terminals are an ideal choice for meeting the requirements of heterogeneous connections. They integrate two connection methods, spring cage and screw, into one terminal. For example, in the STS 2.5 series, the spring side can quickly connect thin wires from sensors, while the screw side can firmly connect thick cables from power sources. This design is particularly practical when it comes to retrofitting projects and interconnecting different standard devices.

Installation and Attachment System Detailed Explanation

A complete wiring plan cannot do without thoughtful accessories. The ST series accessory system includes:

Marking system: Provides central marking slots (compatible with UC-TM or ZB series marking strips) and side marking slots (compatible with UC-TMF or ZBF series) to ensure that each connection point can be clearly and permanently identified.

DIN rail: compatible with standard NS 35/7.5 and NS 35/15 rails. For the MSB series of miniature terminals, it also supports 15mm wide DIN rails for ultra-thin installation.

End plate/partition: such as D-ST 2.5, used to seal the end of the terminal group and increase the creepage distance.

Operating tool: It is recommended to use SZF series screwdrivers (such as SZF 1-0.6X3.5), whose size precisely matches the spring release hole to avoid damaging the terminals.

Key points for interpreting and selecting technical data

When selecting, it is important to pay attention to the following types of technical parameters:

Rated data: According to standards such as IEC 60947-7-1 (straight through type) or IEC 60947-7-2 (protective conductor terminal). Pay attention to distinguishing the rated voltage and current under different certification systems such as IEC, UL, CSA, etc. (for example, ST 2.5 rated current is 24A under IEC and 20A under UL).

Connection capacity: Clearly indicate the maximum and minimum cross-sections that can be connected to solid wires, thin stranded wires, and wires with/without cold pressed ends.

Maximum bridge current: When using a bridge, the current carrying capacity of the entire terminal block may be limited by the bridge itself (e.g. FBS is 24A, while FBSR is 17.5A), rather than individual terminals.

Stripping length: Strictly follow the stripping length provided in the manual (such as 8-10mm for 1.5mm ² terminals and 25mm for 35mm ² terminals) to ensure that the spring can provide the best clamping force.