Crimp Pull Test: Procedure, Standards, and Minimum Force Values

The crimp pull test — also called a pull-out test or tensile test — measures the force required to separate a crimped terminal from its wire conductor. It is the primary destructive test used to verify that a crimp connection meets minimum mechanical strength requirements.

A properly crimped terminal should withstand forces well above the minimum specification. When it doesn’t, the root cause is almost always traceable to incorrect crimp height, worn dies, wrong wire gauge, or improper wire insertion.

Step-by-Step Procedure

Step 1: Specimen Preparation

Cut wire to a suitable length (typically 150-200 mm). Strip insulation from one end. Crimp the terminal at the specified crimp height. Visually inspect for wire brush (0.5-1.0 mm of visible strands) and any cut or broken strands.

Step 2: Neutralize Insulation Support

IPC/WHMA-A-620, UL, USCAR, and most standards require that the insulation crimp wings are opened or peeled back before testing. This ensures only the conductor crimp barrel is being tested, not the insulation grip. Without this step, the insulation grip adds false strength to the measurement.

Step 3: Mount the Specimen

Secure the terminal in a slotted fixture plate. The fixture must hold the terminal without applying pressure to the crimp area itself. Feed the wire into a cable-cam grip or jaw grip that self-tightens under load.

Step 4: Align

The wire and terminal must be aligned axially — in a straight line — to ensure a pure tensile load without bending forces.

Step 5: Apply Force

The tester’s crosshead pulls at a constant, controlled speed until failure occurs. The peak force at failure is recorded automatically.

Test speeds by standard:

Standard	Pull Speed
IPC/WHMA-A-620	25 mm/min
ASTM B913	25 mm/min
UL 486A-486B	25 mm/min (hold for 60 seconds)
USCAR-21 (automotive)	50-250 mm/min (100 mm/min preferred)
NASA-STD-8739.4	25.4 mm/min (1 inch/min)
DEF STAN 59-71	25-50 mm/min

Step 6: Record Results

Record the peak force and the failure mode:

• Wire break — strands fracture before leaving the barrel
• Pull-out — terminal separates cleanly from the wire
• Barrel deformation — barrel opens or splits during the test

Important: If a test is interrupted for any reason, the specimen must be discarded. Partial loading may have damaged the crimp, making continued testing unreliable.

Minimum Pull Force Values

UL 486A-486B (North American Standard)

AWG	Cross-section (mm2)	Min. Force (lbf)	Min. Force (N)
26	0.13	3	13
24	0.20	5	22
22	0.33	8	36
20	0.50	13	58
18	0.82	20	89
16	1.3	30	133
14	2.1	50	222
12	3.3	70	312
10	5.3	80	356
8	8.4	90	400
6	13.3	100	445
4	21.2	140	623

These are minimum values. A properly crimped connection typically exceeds these by 30-50%. Terminal manufacturers often publish their own specifications that may be higher than the standard minimums.

Interpreting Results

Wire Break at or Above Minimum Force = PASS (Ideal)

The crimp is stronger than the wire itself. This is the ideal outcome — it means the crimp barrel has sufficient grip to hold the conductor beyond the conductor’s own breaking strength.

Pull-Out at or Above Minimum Force = PASS (Marginal)

The terminal separated from the wire, but only after exceeding the minimum force requirement. The crimp is adequate but not optimal. Investigate whether crimp height can be adjusted to improve grip strength.

Pull-Out Below Minimum Force = FAIL

The crimp does not meet the minimum specification. Common causes:

• Crimp height too high (under-crimped) — insufficient barrel compression
• Wrong wire gauge — wire too small for the terminal
• Incomplete wire insertion — conductor not fully seated in the barrel
• Worn crimper dies — barrel deformation insufficient
• Wrong terminal/wire combination — engineering specification error

Test Methods Compared

Method	Type	What It Measures
Pull-and-Break	Destructive	Increasing force until failure. Records peak force. Most common method.
Pull-Hold-and-Break	Destructive	Force held for a duration (e.g., 60 seconds per UL 486A), then increased to failure. Combines endurance and strength.
Pull-and-Return (Proof)	Non-destructive	Force applied to a specified value, then released. Specimen survives undamaged. Used for 100% production testing.
Pull-and-Hold (Proof)	Non-destructive	Force applied and held for a specified duration. Specimen must survive.

Destructive testing provides the actual ultimate tensile strength but consumes the specimen. Used for sampling.

Proof testing verifies minimum force without destroying the part. The tested part can still be shipped. However, proof test force must be set below the minimum destructive pull force to avoid weakening the crimp.

Testing Frequency

Event	Pull Test Required?	Sample Size
New terminal/wire combination	Yes	3 samples
Start of production run	Yes	First article
Every 2-4 hours during production	Yes	1 sample
After die change or adjustment	Yes	3 samples
End of production run	Yes	Last article
New wire spool/reel	Yes	1 sample

Equipment

Manual Bench Testers (500-2,000 N)

Hand-lever operation with a calibrated load cell. Suitable for basic production QC. No speed control — the operator controls pull rate manually. Lower cost but less repeatable than motorized testers.

Motorized Bench Testers (up to 10,000 N)

Motor-driven crosshead with controlled speed, digital display, and data logging. This is the recommended type for standards-compliant testing. The constant pull rate eliminates operator variation and ensures repeatable results.

AMT Push & Pull Load Tester

AMT’s Push & Pull Load Tester operates at 230V, weighs 11 kg, and features automatic peak value recording with high accuracy and reproducibility. Designed for crimp pull testing and other force measurement applications in wire harness manufacturing.

Standards Reference

IPC/WHMA-A-620

The primary wire harness standard. Specifies pull testing requirements by class:

• Class 1: Per quality plan
• Class 2: First article + periodic sampling
• Class 3: First article + every lot, with stricter documentation

UL 486A-486B

North American wire connector standard. Specifies minimum pull-out force by wire gauge (table above). Requires the force to be maintained for 60 seconds — the conductor must not separate during the hold period.

USCAR-21

Automotive standard. Pull rate of 50-250 mm/min (100 mm/min preferred). Designed for connections that must survive 15 years and 150,000 miles of automotive service conditions including vibration and thermal cycling from -40 to +125 degrees C.

How the Three Standards Differ

Aspect	IPC-A-620	UL 486A-486B	USCAR-21
Scope	Wire harness assembly	Wire connectors (safety)	Automotive crimped connections
Pull speed	25 mm/min	25 mm/min + 60s hold	100 mm/min (preferred)
Classes	3 quality classes	Single standard	Single standard
Focus	Workmanship acceptance	Safety certification	Automotive durability
Geography	Global	North America	US automotive (SAE)

For a detailed comparison, see our article on wire crimping standards compared.

Conclusion

Crimp pull testing is essential for validating the mechanical integrity of crimped connections. It should be part of every wire harness manufacturer’s quality program — from first-article verification to periodic production sampling.

The key is consistency: use a motorized tester with controlled pull speed, follow the appropriate standard for your industry, and maintain documentation for audit readiness.

Anjali Machine Tools provides the Push & Pull Load Tester for crimp pull testing, along with crimp analysis services for comprehensive quality validation. Contact us for equipment enquiries or testing services.