Special considerations for military connectors

A colleague in the standards community once pointed out that “The nice thing about standards is that there are so many of them.”

Military standard connectors clearly illustrate the wisdom in his statement.

Military standards bodies have done their best to specify individual connectors in such a way that multiple sources can be used without issues regarding reliability or intermateability.  To accomplish this, military specs have been written around specific applications and environments, for example:

• MIL-DTL-38999 Cylindrical Connectors: includes connectors used to attach cables to each other or to electronics boxes in a wide variety of applications in vehicles, ships, planes, and hand held equipment of all kinds.  These families are also used in many non military, but rugged applications in transportation and rugged equipment markets.  The 38999 specification defines families of shells that intermate to provide protection from shock, vibration, and moisture. Inside the connectors are inserts that can be configured for a wide variety of contacts arrangements.

But, when you read these specifications, you realize that they have really defined a catalog of different connectors, for different environments and applications, all under one umbrella.  How can design engineers know they are selecting the best version for their application?

I suggest, in this case, the design engineer is not “An Army of One,” but should use all the reinforcements available to choose the right connector for the application.  The right connector choice needs to respect the environment where the connector will live.  Not only the traditional temperature, humidity, shock and vibe, exposure to salt spray or other corrosive chemicals; but also, can the boxes and cables using the connector be easily disconnected and reconnected by gloved hands in the dark, under fire?

The first level of reinforcements is your connector distributor, hopefully one with a group dedicated to military applications.  These people can help guide the design engineer past the many mines along the way to finding the right solution.  If you open the catalog for any of the major military connector companies, you will find a bewildering array of “Military Standard” connectors to choose from.  Each line of connectors has its own history and future.  Some are antiques, still in the catalog because they always have been.  Others are specified for exotic environments like space, or under water, but it is hard for the seeker to know the difference. Fortunately some of the lines are high-running, broadly used connector families that have been, and will be around for many decades.  This is where you normally want to be.

Fortunately, the distributor sales person is motivated to also sell what is on the shelf and sold in volume.

Therefore, I recommend the following selection process:

• Identify number of conductors you need and amount of current for each
• Configuration details
• Cable to cable – Cable diameter and grounding requirements
• Cable to board – Vertical or right angle
  • Environmental requirements
  • Temperature range
  • Vibration and shock
  • Level of protection from moisture
  • Dimensional constraints

Then contact your distributor or OEM

They should be able to lead you toward the most commonly available solutions and:

• Help you avoid specifying end-of-life or low volume hard-to-get connectors
• Help you end up with a solution with multiple sources
• Can recommend the right contacts, accessories,  and tooling you will need

The closer to the mainstream you can stay for military connectors, the happier you will be. Military connector distributors are valuable allies to have.