In high-current scenarios such as new energy, power engineering and industrial control, terminal crimping is the core process to ensure safe electrical connection. Statistics show that 35% of electrical fires are caused by loose or poor terminal connections. As a key parameter of crimping process, compression ratio directly determines the mechanical strength and electrical conductivity of connections. This article elaborates on the optimal compression ratio range, calculation formula, influencing factors and practical operation essentials for high-current terminal crimping, which can be put into practice immediately.
I. What is Compression Ratio? Grasp its core definition first
Compression ratio (also known as compression rate or compaction rate) measures the change ratio of conductor cross-sectional area before and after crimping, reflecting the fitting tightness between conductors and terminals. There are two mainstream calculation methods in the industry.
USCAR-21 (Commonly used in automotive and power fields, compression rate)
Compression Ratio (%) = 100×(1 - Conductor cross-sectional area after crimping / Nominal conductor cross-sectional area before crimping)
Example: A 50mm² conductor before crimping has its cross-sectional area reduced by 20% after crimping, with a compression ratio of 20%.
VW 60330 (Widely used in German standards and industrial fields, compaction ratio)
Compression Ratio (%) = Conductor cross-sectional area after crimping / Nominal conductor cross-sectional area before crimping × 100%
Example: If the post-crimp conductor area accounts for 80% of the original area, the compression ratio is 80%.
II. Optimal Compression Ratio Range for High-Current Terminal Crimping
Core requirements for high-current applications (copper conductors, 6–400mm²): low contact resistance, high pull-out strength, excellent temperature resistance and vibration resistance. The applicable ranges vary by material and working scenario.
1. Copper conductors (most commonly used in new energy, power and industrial control industries)
General optimal range: 15%–25% (compression rate) / 75%–85% (compaction ratio)
Subdivided scenarios:
Ordinary high current (6–95mm²): 18%–22% compression rate, balancing resistance and strength.
Extra-large current (120–400mm²): Compression ratio 22%–25%. Higher pressure is required to break oxide layers.
High-frequency vibration (new energy vehicles / locomotives): 15%–20% compression ratio, prevent wire strand breakage from over-compression.
2. Aluminum conductor (power cable / busbar)
Aluminum is prone to oxidation and has poor ductility. A higher compression ratio is needed to break oxide film: 30%–50% compression ratio, 50%–70% compaction ratio
3. Industry Standard References
National Standard GB/T 14315-2008: Power cable crimping compression ratio 20%-30%
IEC 60352-2: Solderless crimping compression ratio 15%–25%
USCAR-21 (Automotive Standard): Compression ratio 15%–20%, void ratio ＜10%
III. Consequences of Excessively High or Low Compression Ratio
✅ Low compression ratio (<15%)
Loose fitting between conductor and terminal, sharp rise in contact resistance. Severe heat generation under high current with temperature rise over 50℃.
Insufficient pull-out strength, less than 80% of standard value, prone to loosening and falling off under vibration.
Large gaps allow moisture and dust ingress, accelerating oxidation and corrosion.
✅ Excessively high compression ratio (>30%)
Excessive deformation or even strand breakage of copper wires, reduced current-carrying capacity.
Terminal wall cracking and deformation leading to loss of mechanical strength.
Local stress concentration causes cracking under long-term thermal expansion and contraction.
IV. Three Key Factors Determining Suitable Compression Ratio
1. Conductor material
Copper: Good ductility, compression ratio 15%-25%
Aluminum: Hard oxide layer, compression ratio 30%-50%
Copper-clad aluminum: Intermediate range, compression ratio 20%-30%
2. Terminal type
Tube terminal (OT/UT): 18%–22% compression ratio, hexagonal die preferred
Open terminal (SC): 20%–25% compression ratio, compact open edge required
New energy high-voltage terminal (LV): 15%–20% compression ratio, anti-strand-break design
3. Crimping tools and dies
Hydraulic crimping pliers (16–24t): Suitable for 6–400mm², stable compression ratio 20%–25%
Hexagonal die: Uniform stress, compression error ＜±2%, preferred choice
Round die: For simple use only, large error ±5%, not recommended for extra-large current
V. Practical Operation: Compression Ratio Control & Quality Inspection
1.Precision Control Procedures
Specification matching: Match terminals, dies and cable cross-section one-to-one
Stripping treatment: Stripping length equals ferrule depth plus 1-2mm, keep strands intact without oxidation or burrs
Conductive grease application: Apply compound grease on copper conductors and special grease on aluminum conductors to remove oxide film
Crimping operation: Insert conductor fully, pressurize to rated value, hold pressure for 3-5 seconds, crimp 2-3 positions
Compression verification: Measure outer diameter after crimping, control ratio error within ±2%
2. Mandatory Quality Inspection Criteria
Appearance: No cracks, bulges or exposed conductors, uniform indentation
Dimension: Outer diameter deviation ≤±5%, compression ratio within specified range
Electrical: Contact resistance ≤1.1 times that of equal-length conductor, temperature rise ≤30℃ after 1-hour high-current test
Mechanical: Pulling force meets standard (stranded conductor ≥80N), no looseness or broken strands
VI. Summary: Key Figures for High-current Crimping
Copper conductor (6–400mm²): Optimal compression ratio 18%–22%, compaction ratio 78%–82%
Aluminum conductor: Compression ratio 30%–50%
Core principle: Avoid insufficient or excessive crimping. Match dies, precise control and strict inspection to eliminate loose connection risks.
Post time: May-25-2026