Terminal Blocks (optional): Temperature Range -40°C to +120°C

Q: Why are terminal blocks optional in some PLC racks?

They are optional because some PLC systems use integrated connectors or plug-in I/O modules with built-in terminals. However, separate terminal blocks offer advantages like easier wiring, better organization, and the ability to use different terminal types (e.g., spring clamp vs. screw) based on application needs.

Q: What are the main types of terminal blocks used with PLCs?

Common types include screw terminals (for secure, high-current connections), spring clamp terminals (for quick, tool-free wiring), push-in terminals (for fast installation), and feed-through terminals (for daisy-chaining). Specialized types include fuse, disconnect, and relay terminals for added functionality.

Component Specifications

Definition

Terminal blocks are electromechanical components used to terminate and connect multiple electrical wires within control panels, particularly in PLC racks. They consist of an insulating body (typically plastic) and conductive metal terminals (screw, spring, or push-in type) that clamp wires securely. In PLC systems, they serve as interface points between field devices (sensors, actuators) and the PLC's I/O modules, allowing for organized, reliable wiring and easy maintenance without soldering.

Working Principle

Terminal blocks work by providing a mechanical clamping mechanism (via screws, springs, or levers) that holds stripped wire ends against a conductive metal terminal. This creates a low-resistance electrical connection. The insulating body prevents short circuits between adjacent terminals and to ground. In PLC racks, they channel signals from field wiring to the PLC's input/output cards, enabling centralized control and monitoring.

Materials

Insulation: Polyamide (PA66), polycarbonate (PC), or thermoset plastics (UL94 V-0 rated for flame resistance). Conductors: Copper alloy (often tin-plated or nickel-plated for corrosion resistance), brass, or phosphor bronze. Clamping elements: Steel or copper alloy.

Technical Parameters

Parameter	Typical range	Notes & selection driver
Pitch	2.5–10.16 mm (common: 5.0 mm, 5.08 mm)
Mounting	DIN rail (TS35/TS32), panel mount
Wire Size	0.08–300 mm² (AWG 28–600 MCM)
Current Rating	Up to 300A (varies by type)
Voltage Rating	Up to 600V AC/DC
Protection Class	IP20 (standard) to IP67 (sealed)
Temperature Range	-40°C to +120°C

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

IEC 60947-7-1, UL 1059, DIN 46277, ISO 8820

Parent Products

This component is used in the following industrial products

Main PLC Rack

The primary mounting and housing structure for Programmable Logic Controller (PLC) modules within a control system cabinet.

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Engineering Analysis

Risks & Mitigation

Loose connections leading to overheating or signal loss
Incorrect wiring causing short circuits or equipment damage
Corrosion in humid environments degrading conductivity
Vibration loosening screw-type terminals over time

FMEA Triads

Trigger: Insufficient torque on screw terminals
Failure: High contact resistance, overheating, and potential fire hazard
Mitigation: Use calibrated torque tools and follow manufacturer specifications; consider spring clamp terminals for vibration-prone applications

Trigger: Wire strand breakage due to repeated bending
Failure: Intermittent connections and signal dropout
Mitigation: Use ferrules on stranded wires, provide strain relief, and avoid sharp bends in wiring

Trigger: Environmental contamination (dust, moisture)
Failure: Insulation breakdown or corrosion, leading to short circuits
Mitigation: Select IP-rated terminal blocks (e.g., IP67 for harsh environments) and use protective enclosures

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

Terminal blocks must maintain electrical continuity with contact resistance <5 mΩ, withstand rated voltage without breakdown, and meet mechanical durability standards (e.g., 250+ insertion cycles).

Test Method

Testing per IEC 60947-7-1 includes dielectric strength tests (high-voltage AC withstand), temperature rise tests under load, mechanical strength tests (wire pull-out force), and environmental tests (humidity, corrosion resistance).

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

Verify equipment lists, process limits, capacity, and representative production evidence.

Inspection readiness

Confirm test methods, calibrated equipment, sampling plans, and traceable reports.

Supplier transparency

Check the legal entity, factory address, ownership, certifications, and direct contacts.

CNFX does not score or rank suppliers. Buyers must verify all claims and documents with the legal manufacturer before ordering.

Manufacturers of Terminal Blocks (optional)

Manufacturer profiles associated with Terminal Blocks (optional).

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Frequently Asked Questions

Why are terminal blocks optional in some PLC racks?