Have you ever been asked to perform a Dry Circuit Test?
What do you do? If you build cable and wire harness assemblies should “Dry Circuit Testing” be of concern to you? Dry circuit tests do have their place, but not during the production of cables and harnesses.
What is Dry Circuit Testing?
Dry Circuit Testing is used after Environmental Stress Tests to Detect Contaminates and Oxides on Mating Contact Surfaces.
Typically, a dry circuit test is performed in conjunction with environmental stress tests intended to create contamination or metal oxides on connector contact surfaces. A Dry Circuit test is not particularly relevant until these environmental stresses are applied and the oxides and contaminates are deposited on the contact surfaces.
(Think of deposits built up on a drinking glass subjected to repeated washing and drying cycles in hard water. On electrical contacts, these contaminates interfere with a good connection.)
Low Voltage, Low Current is Used to Avoid “Wiping Away” the Contaminates
Excessive current through the contacts during testing can cause a physical change in the contact area on a microscopic level. Current can cause heating, which can soften or melt the contact points and surrounding area. The contact area enlarges, resulting in a reduction in resistance.
To avoid “wiping away” the contaminates, a dry circuit method is used for testing. A dry circuit is one in which the voltage and current are limited to levels that can’t cause changes in the physical and electrical condition of the contact junction. Generally that means the open circuit voltage is 20mV or less and the short circuit current is 100mA or less.
Why Dry Circuit Testing is not Practical for Production Testing. Contaminates are usually wiped away during connector mating. A “dry circuit test” could be helpful in your production cycle if you were checking for oxides and contaminates on the mating surfaces of your connectors. However, there is one big problem with this idea; the wiping action between mating contacts during connector engagement in production testing usually wipes clean the contaminates, invalidating the test (it would be like testing for the white build-up on a water glass after someone has polished away the hard water deposits with a rag).