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When a power cord is pulled, the strain relief should take the load before it reaches the conductors or terminals. If that load is transferred into the termination, the wires can shift, loosen, or fatigue over time.
This is why cord sets are tested for pull force and strain relief performance. The test applies a defined load to the cable and checks whether the cord remains securely anchored without damaging the conductors, terminals, or insulation.
The required force depends on the applicable standard, cord type, and construction. Those test values turn a simple design feature into a measurable safety requirement.
What Cord Anchorage Has to Do
Cord anchorage secures the cable jacket to the connector body so pulling and twisting forces do not reach the conductor terminations. In a rewirable connector, the requirement is straightforward: the conductors must be protected from strain where they enter the terminals.
The anchorage method depends on the connector construction. Rewirable types typically use a clamp, such as a screw-down bar or saddle, to grip the outer jacket. Non-rewirable connectors may use a crimp sleeve or an overmolded body that locks the cable in place during molding.
What matters is not just how firmly the cable is held at assembly, but whether the anchorage continues to hold after repeated pull and torsion tests.
The Pull Test, and How Many Pulls
IEC 60320-1 handles this in clause 22.2, and the test is short. The cord is pulled 100 times, then twisted with a torque applied for one minute. On rewirable parts the torque figure is two thirds of the tightening torque given in the standard’s screw table.
The acceptance criteria carry more weight than the force:
Other standards use different counts, so buyers should ask for the exact figure rather than a general claim. The rewirable portable socket-outlet standard runs the pull 25 times, at 30 N on a 1.5 mm2 cord and 60 N on a rubber cord, each followed by a one-minute torque test. IEC 60335-1 clause 25.15 uses 30 N, 60 N, 80 N or 100 N depending on the appliance, again 25 times.
Cord size sets the clamp geometry. A 60227 IEC 53 cord measures about 8.0 mm across the jacket at 3 x 0.75 mm2, 8.4 mm at 3 x 1.0 mm2 and 9.8 mm at 3 x 1.5 mm2. A clamp built around one of those diameters will not hold the others with the same force, so a connector offered for two cord sizes needs a clamp that covers the range.
- The cord is not damaged during the test
- After the test the cord has not been displaced by more than 2 mm
- On rewirable connectors the ends of the conductors have not moved noticeably in the terminals
- On non-rewirable connectors there is no break in the electrical connections
Twist and the Two Millimeter Limit
Twisting does as much damage as pulling. A cord gets coiled, wrapped around an elbow and yanked out of a rack, and each of those motions puts torque into the anchorage. That is why the pull test is paired with a torque test and why the limit covers both directions.
A plain tug at the cord end is a useful field check. Pull the jacket rather than the conductors and watch where the cord enters the housing. Visible movement of the jacket, or exposed copper, means the anchorage has stopped working.
Molded assemblies come at the same problem from the other direction, with the jacket bonded to the housing instead of clamped to it. The trade-offs are set out in the guide to overmolded cable assemblies.
Flexing Test Requirements at the Cord Entry
A power cord is usually flexed many more times than it is pulled, so the bend test is designed to run for a much higher cycle count. Published cord-set procedures commonly specify 10,000 flexing cycles at the point where the cable enters the connector. Some European requirements use the same 10,000-cycle target at 60 cycles per minute, with a defined load applied to the cord during the test.
The purpose is to check what happens where repeated bending is concentrated. Fine-stranded copper can fatigue over time, especially close to the termination. Crimped and soldered joints also respond differently to repeated movement because they distribute mechanical stress in different ways. That comparison is covered in crimping versus soldering.
For the finished assembly, the cord entry, strain relief, and termination all have to survive the same service life. A connector may be designed for thousands of mating cycles, but that rating has little value if the cable fails first at the point where it enters the housing.
Other Mechanical Tests
Cord anchorage is only one part of the mechanical qualification. Depending on the connector and applicable standard, testing may also include:
These tests rarely appear in a short product description, but they help explain why connectors with similar dimensions and electrical ratings can perform very differently after years of use.
- Free-fall testing in a tumbling barrel, with the number of drops based on component mass.
- Lateral loading of contacts and impact testing with a spring hammer.
- Combined torque and pull tests on the assembled connector.
- Pin-retention tests using a defined force and duration.
- Ball-pressure, heat-aging, and material-aging tests for thermoplastic and elastomeric parts.
Common Signs of Anchorage Failure
Anchorage problems usually show up in a few recognizable ways. The jacket may pull back from the housing, exposing insulated conductors or copper near the entry point. A protective-earth connection may become intermittent and only fail when the cord is moved. In other cases, the cord entry begins to run hot because movement at the termination has increased contact resistance.
That last symptom can be misleading. Heat near the plug or connector is often blamed on the current rating, when the real problem is a termination that has loosened or shifted under repeated mechanical load.
For more on temperature limits and how they are specified, see power cord temperature ratings.
What to Include in the Anchorage Specification
Cord anchorage can be specified quite clearly. A useful drawing or purchase specification should state:
The applicable test clause and number of pulls, such as clause 22.2 with 100 pulls.
The anchorage method: screw clamp, crimp, or molded strain relief.
The cord outside-diameter range and conductor sizes the design must accommodate.
The flexing requirement, including cycle count and applied load.
It is also worth naming the exact cord construction the connector will be used with. A clamp designed for one jacket diameter may not hold another securely, even if the conductor size is similar. Plug type, cord length, and conductor sizing are covered in the guides to choosing power cord plug gauge and length and AWG wire gauge in power cords.
