Cable Assembly Testing: What Are the Different Tests For Cable Assemblies

Custom cable assemblies are everywhere today, serving several applications. You use these assemblies to send power, data, and sensitive signals. These assemblies undergo several mechanical and environmental stresses; thus, you must ensure that all these cable assemblies work fine without any disruption. Cable assembly testing is the only way to ensure their functional ability.

With these tests, you can be sure the assemblies meet the end point’s requirements and prove their future work. Here we talk about all these tests in this blog post.

What is Cable Assembly Testing Required?

Firstly, the primary purpose of a cable assembly is to connect two devices electrically, and for this, you can do electrical continuity testing to check if they are operational. Apart from this, there are other tests, mainly when medical and military applications use cable assemblies like mechanical and environmental tests.

Electrical tests

With electrical testing, you can check the electrical properties of the wire harness or cable assembly and know if there are any open circuits, internal shorts, or faulty connections. 

Electrical continuity tests: As the name clears, you can check whether the current flows through the cable properly. Measure the electrical connection between two test points and the resistance of the circuit. If you notice high resistance, it means there is some fault in the connection.

How to perform the test:

• First, connect the two or more test points to a multimeter (a device that measures resistance or continuity).
• Now, the multimeter will send voltage between the points and measure the resistance within the circuit.
• If there is electrical continuity, the multimeter gives an audible beep; otherwise, it will send an open loop message for an open circuit.

Caption: technician testing cables

Hipot test: You can also call this test a dielectric strength test. It assesses the cable assembly’s insulation layer and detects defects, gaps, or contaminants. You can also find out any short circuits or current leakage if there.

How to perform the test:

• Firstly, you must pass a high voltage of around 10 Kv across the two conductors. This high voltage induces stress on the soldered connections and electrical insulation.
• Check whether the circuit can withstand this high voltage in a short timeframe. If yes, the cable assembly is safe for use with the standard voltage for its entire lifespan.
• You can do it with a single hipot test machine for up to 20 conductors when testing multi-conductor cable assemblies. However, if there are more than 20 conductors, you will have to use thousands of Hipot machines for testing all conductor combinations.

Caption: electrician testing voltage

Milliohm tests: As the name clears, Milliohms tests very low resistance connections in the cable assembly to know the electrical connection’s quality and condition. Mostly, this test help in measuring the ground circuit’s resistance, and the resistance between the ground and the cable is meager, which typical multimeter devices fail to detect. Thus, you need a milliohm test.

How to perform the test:

• Firstly, get a milliohm meter which needs a four-terminal measurement method.
• Apply the current to a part of the cable assembly. Measure the voltage on two terminals and the current on the other two.
• For proper electrical bonding, the resistance measured should be 2.5 between ground points. If it comes out more than this, the cable is faulty.

Mechanical tests

Mechanical tests gauge the strength of the cable assembly and its resilience to fatigue, such as crush resistance, elongation, impact resistance, and tensile strength.

Pull test: With the pull test, you can test the strength of the mating connectors, wires, cables, and crimp joints. Pull the assembly at a specific load and rate them according to the wire and connector type used. When applying the pulling force, use a motorized pull tester to measure the value of the force applied. For example, if you want to check whether a cable can bear 50 pounds of force, you apply the same force and see if the cable remains undamaged after the test.

There are several methods of performing pull tests:

• Pull and break: It is a destructive pull test as you apply the force continuously on a cable until it breaks to check its highest capacity.
• Pull, hold and break: this is also a destructive test where you apply a force and hold it for a specific rate. You increase the pulling force until the wires break or connectors fail.
• Pull and hold: unlike the above two, it is a non-destructive test. Here you apply a force at a specific rate for a certain period.
• Pull and release: Similar to the above, you also apply a pulling force at a specific rate and then remove the force.

Flex/bend test:

Cable assemblies undergo routing, bending, and flexing, which may result in damage. You use flex cables for applications requiring such bending and twisting. The cable assembly must send undisrupted signals, power, and data, irrespective of movement. If you want to evaluate a cable for such bending and twisting for a particular application, perform a flex/bend test.

• While performing the test, attach a flex or bend machine to one end of the cable. 
• Tie the other end to a pretzel shape or attach a weight so that cable bends at 90 degrees angle. 
• For a rolling bend test, you can attach the other end to a swing arm mechanism that constantly moves back and forth in a semicircle arc or 180 degrees arc. 
• Before you start the test, there is a predefined minimum bend radius and number of cycles for a particular cable.

Environmental tests

You use cable assemblies in different environmental conditions, some of which are pretty extreme. Cables in such environments must show resilience; otherwise, they will show premature corrosion, aging, or degradation. Some applications require cable assemblies to comply with standards like IP67 to ensure suitability for a particular environment.

The wide range of environmental tests which a custom cable assembly goes through are:

• Thermal shock
• Waterproofness
• Humidity
• Vibration
• High or low-temperature storage
• Fungus exposure
• Salt spray
• Chemical and fluids exposure

Some of these tests are quite expensive, and you may also need to wait for the chamber availability.

IP66/IP67 water ingress test:

When developing cable assembly specifications, most manufacturers refer to IEC or the International Electrotechnical Commission for giving protection ratings to a cable for a specific application or environment. 

According to IEC, there are three international protection (IP) code standards. Here, you can refer to IP as ingress protection also. 

Every IP code has two numbers; the first indicates the protection rate from dust, dirt, or other solid matter, whereas the second tells the rate of protection from liquid substances like water. So, the code represents their level of protection. 

There are two common Ip ratings for cable assemblies. Most manufacturers design their cable assemblies to meet these conditions. They are:

IP 66 rating: A cable assembly with an IP66 rating means the wires and cables have high protection against dust. The first number, “6,” represents this protection, and the second, “6,” indicates its protection against water ingression through high-powered water jets inclined at any angle.

IP67 rating: In the IP67 rating, the first “6” indicates the cable assembly protection against dust. In contrast, the second number, “7,” represents protection from moisture and water ingression if submerged to a depth of 15cm to 1 m and when held in that position for 30 minutes.

Fungal resilience test:

Warm and humid conditions often produce fungal growth in cable assemblies. The fungal growth occurs mainly in assemblies used in marine conditions with high and prolonged exposure to moisture and darkness. The growth of fungus leads to corrosion, aging, and other damage to the cable jacket, conductors, and connectors. Thus, the cable must go through the fungal test. The common fungal test standard is MIL-STD-810, a US military standard to show that a product is resistant to fungal growth.

While performing the test, material coupled with fungus spore is sprayed on the cable. Now, you place this in a chamber having warm and humid conditions. Regular monitoring is done to check whether there is fungal spore growth and its growth rate.

caption: electrician testing the cables

VSWR testing:

VSWR, or voltage standing wave ratio testing, is a low-less line’s max to min voltage ratio. This test helps measure radio frequency loss in RF cable assemblies and coaxial cables. The perfect ratio is 1:1, and a completely mismatched ratio, i.e., for an open or short circuit, is ∞:1.

In general, there is some loss in the transmission line. To perform the test, you need to detect the forward and reverse power at the testing point on the system. Now, this value is converted to VSWR.

When is the cable assembly testing performed?

Mostly, manufacturers perform tests during the final inspection; however, they need to do some tests after manufacturing to show the correct fabrication of the cable assemblies. Manufacturers either perform the tests on 100% cables built or at a predefined AQL or acceptance quality limit quantity. 

Sometimes, designers and technicians also perform some tests during the manufacturing process to ensure the completion of a particular step. For example, Hipot tests need to be done before heat shrink tubing in the complex cable harnesses. 

All these tests are expensive and time-consuming, so there is no set sequence for performing the tests. Sometimes, you need special equipment for testing cable assemblies, and other times, tests may damage cable assemblies. So, reviewing everything, including user requirements, is always better before setting any test sequence.

Conclusion:

Cable assemblies are complex equipment with multiple connections and terminals, and cable assembly manufacturers need to check all potential failure points. We perform reliable testing on our cable assemblies to ensure the best products suit customers’ requirements. Our products meet the required and toughest standards to withstand mechanical, environmental, and electronic stresses.