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A Summary of A-620 Cable Testing Standard
What is IPC/WHMA A-620?
The IPC/WHMA-A-620, Requirements and Acceptance for Cable/Wire Harness Assemblies is a joint project of IPC (Institute of Printed Circuits) and WHMA (Wire Harness Manufacturers Association). Originally released in 2002, the IPC/WHMA-A-620 has become the industry standard against which to measure quality.
It describes acceptable assemblies based on visual acceptance criteria. The detailed pictures clearly communicate acceptable and unacceptable features of an assembly. It provides a way to train factory floor people and set expectations between customers and suppliers of the level of quality expected. You can purchase the current version at:
What Has Happened on Cable Testing in A-620?
The A-620 was released in 2002 without a "Test" section. Cirris worked with other WHMA and IPC members in creating the test section, which became the major change in the A-620 standard (Rev A released in July of 2006).
Defining Cable Tests and Test Level requirements
The Test Section uses the existing classifications for assemblies based on their intended use as follows:
The standard encourages the use of cable testing requirements defined for the specific assembly as agreed upon by the Assembler and the Customer. As an alternative, specifications can be defined either by the assembler or the customer and agreed on by the other party. In the absence of agreed upon requirements, default requirements have been established.
"Minimum Default" Electrical Cable Test Requirements for Rev A of A-620
Some Questions You Might Have About The A-620 Test Requirements
None of the information on this page is a substitute for having a copy of the A-620 Rev A standard. This information is intended to help guide you in understanding why specific tests and their required parameters are needed.
The DWV test has a "minimum" time and IR has a "maximum" time. Shouldn't they both be minimum times?
The Dielectric Withstand Voltage test (DWV) identifies a sudden breakdown in the insulation between conductors. This test must continue for some minimum time. The same maximum-allowable current threshold is used throughout the test time. Longer times have better chances of detecting faults.
The Insulation Resistance test (IR) detects a more consistent current flow between insulated conductors, stated as a resistance, by factoring in the applied voltage. When the voltage is first applied the current usually peaks and then, due to humidity that might be dried out by the energy of applied voltage and something called "dielectric absorption", it trends lower over time. This means that the measured resistance starts lower and trends higher over time. The longer you apply the voltage, the better the final measured insulation resistance, so longer times allow cables with worse IR performance to pass. To shorten production test time without degrading the test, the IR test time ends as soon as the minimum resistance value is reached.
My Cirris tester has a leakage setting but not a DWV setting. Is the DWV test performed?
When performing a DC high voltage test Cirris testers check for DWV and IR at the same time. This means that the DWV test will last as long as the IR test. While newer Cirris testers have separate IR and DWV settings, the Signature 1000H, 1000H+ and 1000HN testers do not. No matter what IR setting is used in these older models, the DWV test will always be more stringent than the 1 mA DWV limit required in A-620 Rev A.
In Class 2 cables, why are high voltage (HV) tests required for close spaced contacts (<2mm [.079"])? This seems backwards since the closer the spacing the lower the voltage a connector is likely to be able to withstand.
It is true that smaller gaps between isolated conductors result in lower breakdown voltages. They also increase the chance of an intermittent or latent defect in the form of a short. With creepage distance >2mm the likelihood of finding near-shorts with high voltage tests was not thought to offset the cost of the more rigorous HV tests that would be required.
In Class 2, just as in Class 3, small creepage distances can justify a reduction in the voltage applied for the high voltage test. The A-620 requirements specify that electrical tests should operate at such levels as not to degrade the electrical properties. However, the need for a good HV test increases as the spacing gets smaller. The costs of the testing should not increase when the voltage needs to be reduced. As a guide, you can see what problems you might encounter with your particular creepage distance using the Arc Gap Calculator at: http://www.cirris.com/testing/voltage/arc.html
When testing at 1000 VDC the gap must be larger than .15mm, (.006"). At 1500 VDC the gap must be larger than .48mm (.019"). These are rather small creepage distances. The HV test voltage is most likely problematic for very small connectors in Class 3 applications.
I have insulated wires or connectors with a specified maximum working voltage that is lower than those required in the A-620 test specification. Will these test voltages damage them? Am I caught in a double bind where these required test voltages are considered destructive and render the assembly unusable for service?
This question most often arises from those doing work under military contracts where interpretations for different requirements may conflict. If you have a reason to believe that testing will degrade your assembly, then you may want to perform some confirming tests and make use of a provision of the test section that requires electrical tests on good assemblies to not degrade reliability.
We are not aware of any research or proof that the insulation used in good assemblies can be degraded by high voltage during brief applications in the IR and DWV tests. Here are some sound reasons why this is not considered a risk:
If you become aware of research that supports the fear of degrading insulation in wiring or connectors with the short-term application of high-voltage, we would deeply appreciate knowing of it.
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