PLC Cabinet Too Crowded? 3.5mm Push-In Terminals Recover 50% Rail Space
PLC control cabinet miniaturization requires three specific actions:
-
Select 3.5mm-wide push-in terminal blocks instead of 6–8mm screw types—every 100 terminations frees 450mm of DIN rail.
-
Deploy double-level or triple-level stacking to multiply wiring density on the same rail length.
-
Adopt spring-clamp push-in wiring to cut installation time from 13.5 seconds to 3.6 seconds per connection.
These measures deliver measurable space recovery, higher I/O density, and faster assembly without cabinet enlargement.
Push-In vs. Screw Terminals: Head-to-Head Comparison
| Comparison Metric | Screw Terminal | Push-In Terminal |
|---|---|---|
| Width per pole | 6.0 – 8.0 mm | 3.5 mm |
| Rail space for 100 points | 600 – 800 mm | 350 mm |
| Solid wire connection time | 13.5 sec | 3.6 sec |
| Flexible wire connection time | 14.4 sec | 4.1 sec |
| Installation tool required | Screwdriver + torque wrench | None |
| Vibration performance | Prone to loosening, needs maintenance | Spring maintains constant pressure |
| Maximum stacking levels | 1 level per position | Up to 8 levels (32 connection points) |
The width reduction alone—from 6–8mm down to 3.5mm—recovers 40–50% of DIN rail length. For control cabinets with hundreds of terminations, this translates into tangible space for additional I/O modules or a smaller enclosure footprint.
Standards and Certifications That Matter
Control panel engineers must verify that terminal blocks comply with industry safety benchmarks. Push-in terminal blocks are designed to meet IEC 60947-7-1 for low-voltage switchgear and controlgear assemblies, as well as UL 1059 for terminal block safety standards. Additional specifications include:
-
Flammability rating: UL94 V-0
-
Operating temperature range: -40°C to +105°C
-
Shock and vibration testing per IEC 60068-2-6
These certifications confirm that push-fit DIN rail terminals withstand industrial environments without compromising connection integrity.
Selection Guide: Matching Terminals to Application
Selecting the correct push-in type terminal block depends on three parameters:
-
Wire cross-section: 0.14 – 1.5 mm² suits PLC digital I/O signals; 1.5 – 4 mm² handles analog signals and small loads; 4 – 6 mm² serves power distribution.
-
Rated current: 16A covers standard control circuits; 24A supports actuator supply; 32A accommodates drive and power circuits.
-
Stacking level: Single-level for general signal connections; double-level for I/O-dense zones; eight-level marshalling blocks (32 connection points) for PLC signal concentration and DCS distribution.
Vibration Resistance: A Critical Advantage
Industrial machinery generates continuous vibration that gradually loosens screw terminals. Push-in spring clamp technology maintains constant contact pressure regardless of mechanical stress or thermal cycling. Laboratory testing per IEC 60068-2-6 subjects terminals to vibrations up to 300 Hz with 5mm displacement across three axes for two hours each. Push-in type terminal blocks preserve milliohm-level contact resistance throughout, eliminating the intermittent faults that plague screw-type connections in high-vibration environments.
Integration and Mixed Installations
Push-in terminal blocks mount on standard 35mm DIN rails per EN 60715, compatible with NS 35/7.5 and NS 35/15 profiles. This standards alignment enables phased upgrades—screw terminals and push-in blocks can coexist on the same rail, allowing gradual migration during scheduled maintenance without cabinet rework.
Frequently Asked Questions
Q: What is the minimum width of a push-in terminal block?
A: 3.5mm per pole, compared to 6–8mm for conventional screw terminals.
Q: How much faster is push-in wiring than screw terminals?
A: Solid wire connections take 3.6 seconds vs. 13.5 seconds; flexible wire takes 4.1 seconds vs. 14.4 seconds—a 60–65% reduction.
Q: Are push-in terminal blocks vibration-resistant?
A: Spring clamp technology maintains constant contact pressure under continuous vibration, eliminating the loosening issues common with screw terminals.
Q: What standards do push-in terminal blocks comply with?
A: IEC 60947-7-1 and UL 1059, with UL94 V-0 flammability rating.
Q: Can push-in and screw terminals be mixed in the same cabinet?
A: Yes. Both mount on standard 35mm DIN rails (EN 60715), allowing phased upgrades during scheduled maintenance.
