An In-depth Look at MIL-Spec Connectors - D38999 Series III

Introduction to MIL-Spec Connectors

A MIL-Spec connector offers two crucial features:

• Air Seal: The connector is designed to prevent air infiltration, which can bring in moisture leading to corrosion. This feature also protects against the corrosive effect of Ozone on the crimps.
• Magnetic Permeability: In situations where cables are adjacent to a bundle of wire producing an AC signal, the signal may get carried through the cable. To prevent this, MIL-Spec connectors offer high magnetic permeability and are primarily made from materials such as aluminium instead of steel or iron.

About D38999 Series III

MIL-DTL-38999 connectors, available in four series: Series I, II, III, and IV, are renowned for their environmental resistance. They utilize removable crimp contacts and offer an operational temperature range of -65 to +200°C. The Series III, in particular, is preferred for Military and Aerospace applications due to its exceptional performance in extreme conditions such as high temperatures, moisture, wind, and vibrations.

Part Number Selection for D38999 Series III

Selection of the part number for the D38999 Series III involves several steps:

1. Select Shell Type: Series III has shell type identifiers 20, 21, 23, 24, 25, 27 for different receptacle styles, and 26 for plugs.
2. Select Material and Finish: Different identifiers are used to specify the material and finish type such as F, G, H, J, K, L, M, N, S, T, W, Y, Z.
3. Select Shell Size: D38999 connectors are available in 9 shell sizes, identified by: A, B, C, D, E, F, G, H, and J.
4. Select Insert Arrangement: Each shell size has a set of inset arrangements, for instance, size A has 2 insert arrangement options while size J has 12.
5. Select Contact Type: Besides the standard pins (P) and sockets (S), there are other identifiers for sealed and hermetic contacts.
6. Select Keying Position: There are six distinct keying positions available for each shell size in the D38999 series of connectors: N, A, B, C, D, and E. The keying position is indicated by the last letter in the part number.

Assembly Instructions for D38999 Series III

Correct assembly of these connectors requires a few steps:

1. Wire Stripping: Strip wire to the required length and twist strands together to form a firm bundle.
2. Contact Crimping: Insert stripped wire into contact crimp pot and use the correct crimp tool and locator to ensure the indentors are open.
3. Contact Insertion: After crimping, insert the contact into the connector using an insertion tool, ensuring proper alignment and seating.

MIL-Spec "Equivalent" Connectors

In addition to MIL-Spec connectors, some manufacturers produce "equivalent" connectors. These connectors mimic the form factors and ruggedness of the MIL-Spec designs, although they may not adhere strictly to MIL-Spec standards. Major manufacturers such as TE Connectivity, Cinch, and Glenair produce these equivalent connectors under various product families.

Resources

For a comprehensive guide on D38999 Series III connectors, refer to the Federal connectors guide. A glossary can help you understand industry-specific terminology, and instructional videos can guide you on crimping procedures and best practices.