Comparison of MIL-DTL-38999 and MIL-DTL-22992

In aviation Electrical Wiring Interconnection Systems (EWIS), the MIL-DTL-38999 is nearly synonymous with connector testing. The standard is comprehensive, robust, and serves as a good test reference for nearly any electrical connector, even those that do not align with the entire standard. Connectors qualified to the 38999 are considered suitable for rather extreme aviation environments, namely: high vibration areas, SWAMP environments, and even within weapons systems. Because of its robustness, the test/performance requirements of the MIL-DTL-38999 can sometimes be too restrictive for less intense aircraft environments (such as commercial or low-altitude aircraft) or for EWIS connectors that do not align with the construction of MIL-DTL-38999’s “miniature, high density, circular, environment resistant electrical” connectors.

In these cases, other standards may be considered to more closely align with the anticipated needs of an aircraft’s EWIS. In this article, we will compare the well-known MIL-DTL-38999 with a much less restrictive standard, MIL-DTL-22992, and identify many similarities and gaps between the two standards.

Basic Differences

Some of the most obvious differences between standards include the scope and intended use cases of each standard.

	MIL-DTL-38999	MIL-DTL-22992
Temperature Range	-65°C to 200°C	-55°C to 125°C
Minimum Contact Size	23	16
Maximum Contact Size	8	0000
Construction	Miniature, high density, circular, environment resistant electrical connectors with removable crimp contacts Hermetically sealed electrical connectors with fixed non-removable contacts	Multi-contact, heavy duty, quick disconnect, waterproof, electrical plug and receptable connectors and associated accessories
Plug Types	Straight, without spring fingers Straight, with spring fingers that electrically engage receptacle shell prior to contact engagement (series I, III and IV only) Straight, with spring fingers that electrically engage receptacle shell after contacts engage (series II only) Lanyard release	Cable connecting plug (without coupling ring) Straight plug
Receptacle Types	Box mounting, both front and rear panel mounting Wall mounting, both front and rear panel mounting Jam nut, rear panel mounting Solder mounting Thru-bulkhead	Wall mounting receptacle Box mounting receptacle Jam nut receptacle Jam nut receptacle (box) Wall mounting receptacle (with coupling ring – class L only)
Use Cases	Series I – General application within weapon system; high vibration, SWAMP Series II – General application within weapon system; not high vibe or SWAMP; not scoop proof Series III – General application within weapon system; blind mating areas; high vibe at elevated temp; SWAMP Series IV – General application within weapon system; blind mating areas; high vibe at elevated temp; SWAMP	Class C – External interconnection on vans, shelters, trailers, building, heavy duty applications – not for primary power distribution Class J – Same as class C but where a wire support grommet is necessary Class L – Power connections 40-200A, heavy duty, waterproof, arc-quenching. For use only with heavy-duty jacketed cables Class R – General purpose, heavy duty; pressurization and arc quenching not required – not for primary power distribution

Notably, the MIL-DTL-22992 lacks considerations for altitude, flame testing, and thermal aging methods. This is not too surprising given the significantly less severe environments the standard addresses, but it is important to keep in mind these gaps when using MIL-DTL-22992 for connector qualification testing.

Test Alignment

There are a limited number of test methods between MIL-DTL-38999 and MIL-DTL-22992 that align with one another to varying degrees of accuracy. The following table provides a simplified comparison of tests common between both standards.

Test	Referenced Methods		38999	22992
	38999	22992
Air Leakage	EIA-364-02	None	Hermetic only 30 min unspecified conditioning Test pressure differential 1atm	30 min conditioning at -55oC for classes C and J Connector test pressure differential ~ 2atm Protective cover test pressure differential ~1 atm Allowable leakage much greater (by a factor of ~104)
Insulation Resistance	EIA-364-21	EIA-364-21	Performed at ambient or elevated temperature Minimum ambient temperature requirement: 5,000 MΩ (requirement varies after Humidity and Altitude Immersion testing and at elevated temperature)	Ambient temperature only Minimum requirement: 5,000 MΩ
Insert Retention	EIA-364-35	None	Load application rate: 10 psi/s Test load: 100 psi Test load maintained for 5-10s	Load application rate: 10 psi/s Test load varies by connector size Test load maintained for 5s
Dielectric Withstanding Voltage	EIA-364-20	EIA-364-20	Performed at sea level or altitude All contacts tested Test voltage varies based on service rating (sea level values: 1-2.3kVAC)	Performed at sea level only Voltage applied between the two closest contacts and between the shell and contacts closest to the shell Test voltage varies based on service rating (1-7kVAC)
Salt Spray	EIA-364-26	EIA-364-26	Standard test and dynamic test methods Some duration alignment with 22992 50 mating/demating cycles before and after salt spray (dynamic)	Aligns more closely with 38999 dynamic test – exposure with ends mated followed by shorter exposure unmated Some duration alignment with 38999 50 mating/demating cycles before and after salt spray
Contact Resistance	EIA-364-06	EIA-364-06	Higher maximum voltage drop requirement (for sizes covered by both standards)	Lower maximum voltage drop requirement (for sizes covered by both standards)
Hexavalent Chromium Detection	IEC 62321-7-1	IEC 62321-7-1	Same method Same requirement	Same method Same requirement
Magnetic Permeability	EIA-364-54	ASTM A342	Measured by Lo Mu permeability indicator Relative permeability less than 2.0μ	Measured by Lo Mu permeability indicator Relative permeability less than 2.0μ
Shell-to-Shell Conductivity	EIA-364-83	EIA-364-83	Same test method Maximum voltage drop ranges from 1.0 mV to 200 mV depending on connector properties/construction Max voltage drop may increase by 100% after conditioning	Same test method Maximum voltage drop before conditioning: 200mV Max voltage drop may increase by 100% after conditioning
Contact Retention	EIA-364-29	None	Force applied alternately in each axial direction Test load maintained for 6 seconds Greater test loads (for sizes covered by both standards)	Force applied alternately in each axial direction Duration of force application not specified
High Impact Shock	MIL-DTL-901	MIL-STD-202-207	No electrical discontinuity Drop heights of 1, 3, and 5 ft	No electrical discontinuity in excess of 10 µs Drop heights of 1, 3, and 5 ft
Humidity	EIA-364-31	MIL-STD-202-106	10 cycles (cold exposure inclusive) Min insulation resistance during 10th cycle: 100MΩ Post-test DWV	10 cycles (no cold exposure) Min insulation resistance during 10th cycle: 10MΩ Post-test DWV
Fluid Immersion	EIA-364-10	None	11 standard test fluids Varying duration, temperature, and number of cycles for each exposure Connectors may be mated or unmated as specified	2 Test fluids: hydraulic fluid and lubricating oil 20 hour exposure in each fluid, unmated
Contact Engagement and Separation Force	AS39029	EIA-364-37	Hermetic only Different standards, same test procedure Same separation force requirements Lower maximum engagement force requirements	Different standards, same test procedure Same separation force requirements Higher maximum engagement force requirements
Resistance to Test Probe Damage	AS39029	EIA-364-25	Hermetic with sockets only Max engagement force for size 16: 36 oz Min separation force for size 16: 1.5 oz	Size 16 socket contacts only Max engagement force: 36 oz Min separation force: 1.5 oz
Vibration	EIA-364-28	EIA-364-28	No discontinuity or disengagement of mated connector ends Test condition VI of EIA-364-28	No electrical discontinuity in excess of 10 µs Test condition III of EIA-364-28

Similar Intent – Different Tests

Some test methods between the standards have different titles/methodology but align in intent. Typically, this is to account for the different expected use cases of each qualification standard.

An example of this is the MIL-DTL-38999’s Altitude Immersion and the MIL-DTL-22992’s Water Immersion methods. These methods seek to determine if the sample connector is vulnerable to water ingress. Both methods primarily consist of immersion in water, but the main difference is the altitude at which the test is performed. As mentioned above, altitude consideration is not a factor in MIL-DTL-22992. If the connector under test is expected to operate in water-laden conditions at altitudes well above sea level, the MIL-DTL-38999 test may be the preferred option for qualification, even if the connector is not intended for military combat applications.

Test Gaps

There are many MIL-DTL-38999 test methods that are not included in the MIL-DTL-22992 standard; this is unsurprising considering the different application severities identified by each standard. Arguably more interesting are the test methods unique to the MIL-DTL-22992:

• Shell-to-Shell Contact Resistance Grounding – A voltage drop measurement exclusive to ‘arc-quenching’ connector grounding contacts.
• Heat Rise – A four-hour rated DC current application after which the temperature of each terminal is measured.
• Cable Pull-Out – An axially applied pull force evaluating the connector adapter’s ability to hold the cable in place without the assistance from the connector-to-contact attachment.
• Arc Rupture – Repeated mating/demating of powered connector ends to evaluate any resulting arc damage
• Tensile (Protective Cover Chain) – A tensile pull test to evaluate the protective cover attachment chain to resist external force applications.
• Abrasion – Repeated cycles of abrasion applied to panels representing the finish/plating of the connector shell or accessory hardware.

As mentioned above, the MIL-DTL-22992 does not account for considerations of flame exposure, altitude, or thermal aging. This is demonstrated in the absence of familiar MIL-DTL-38999 tests such as Firewall, Altitude-Low Temperature, Thermal Shock, and Temperature Cycling. In circumstances where these properties may affect performance, MIL-DTL-22992 would not provide sufficient results to confirm connector quality for the application.

Arc Rupture

One method that stands out in the MIL-DTL-22992 is the Arc Rupture test. Put simply, connectors undergo 50 continuous mating/demating cycles while carrying test current. As the connector ends are separated and/or connected, the distance between mating electrical points varies. The closer each pin and socket are to one another, the more likely the air between the two will break down into an electrical arcing event (Picture the small electrical arcs that sometimes occur when plugging a device into a wall outlet, particularly when the device’s switch is in the “ON” position). Electrical arcs, even relatively small ones (in AIR6982 these are called “high impedance arcs” or “series arcs”), can result in equipment damage that will affect reliable functionality. The intent is to identify electrical and mechanical damage resulting from electrical arcs that would prevent the mating/demating of the connector ends by normal means.

There is no method in MIL-DTL-38999 with the same performance or intent as the Arc Rupture test of MIL-DTL-22992. Rather, the 38999 connectors are built with more robust coupling mechanisms and require more mechanical testing (Coupling and Uncoupling Torque, Durability, External Bending Moment, Bayonet Coupling Pin strength, etc.) to the extent that accidental demating of powered connectors is not considered a risk.

Conclusion

Ultimately, the planned testing conditions for EWIS components should represent the anticipated vehicle operations and environment. This may mean making changes to standard values or referencing any number of different standards. It is important to explore many testing options to develop a comprehensive qualification plan and ensure sufficient safety in the final aircraft design.

For those looking for guidance or testing regarding connector qualification, contact Lectromec today. Our ISO 17025:2017 accredited lab is ready to help.