WIRE, ELECTRICAL, POLYTETRAFLUOROETHYLENE/POLYIMIDE INSULATED, NORMAL WEIGHT, NICKEL COATED, COPPER CONDUCTOR, 260 °C, 600 VOLT ROHS AS22759/87D

DOI: https://doi.org/10.4271/AS22759/87D

Issuing Committee: AE-8D Wire and Cable Committee

Publisher: SAE International

Pages: 6

Rationale: SPECIFICATION UPDATED TO INCLUDE AS29606 CONDUCTOR REQUIREMENTS, ROHS RESTRICTIONS AND AS22759 MODIFICATIONS. THIS CHANGE ALSO INCREASES THE MAXIMUM WEIGHT REQUIREMENTS FOR WIRE SIZES 8 THROUGH 02 TO ACCOUNT FOR INCREASED CIRCULAR MIL AREA (CMA) ADOPTED IN AS29606. AS22759 IS A CONVERTED MILITARY SPECIFICATION ORIGINALLY NOTED AS MIL-W-22759 CREATED IN 1971. CONDUCTOR REQUIREMENTS WERE ORIGINALLY DEFINED BY ASTM B3, B298 AND B355 FOR TIN, SILVER AND NICKEL PLATE RESPECTIVELY. THESE SPECIFICATIONS CONTROLLED THE CONDUCTOR BY ESTABLISHING STRAND SIZE, CONDUCTOR SIZE AND MAXIMUM DCR (DIRECT CURRENT RESISTANCE). BY THE LATE 1980'S CONDUCTOR PRODUCERS WERE PRODUCING TIGHT TOLERANCE CONDUCTORS WHICH WERE MADE AT THE MINIMUM DIMENSIONAL AND MAXIMUM DCR LIMITS OF THE SPECIFICATION TO REDUCE THE WEIGHT (MASS) OF THE FINALLY INSULATED WIRE. BY THE EARLY 1990'S THE TIGHT TOLERANCE CONDUCTORS WERE PREVALENT THROUGHOUT AEROSPACE. ABOUT THE SAME TIME, LARGE GAUGE SIZE CONDUCTORS (SIZE 8 THROUGH 4/0) STARTED EXHIBITING CRIMP FAILURES IN TERMINAL LUGS MOUNTED ON AIRCRAFT GENERATORS. SINCE THESE CIRCUITS ROUTED PRIMARY ELECTRICAL POWER FROM THE GENERATOR TO THE MAIN POWER DISTRIBUTION CENTERS, CRIMP DEGRADATION RESULTING IN DISRUPTION OF ELECTRICAL POWER CAUSED SIGNIFICANT CONCERN. SEVERAL OEM'S AS WELL AS NAVY AND AIR FORCE LABORATORIES INVESTIGATED THE FAILURES AND DETERMINED THAT THE FAILED CRIMPS WERE DUE TO A COMBINATION OF LOW CMA, HIGH VIBRATION AND THERMAL CYCLING. ADDITIONAL TESTING ESTABLISHED MINIMUM CMA LEVELS WHICH WOULD PREVENT THE CRIMP FAILURES. THESE NEW LIMITS WERE OFFERED TO ASTM BUT REJECTED. NAVAIR THEN PRODUCED AN ENGINEERING POSITION LETTER (EPL) TO MANDATE THE INCREASED CMAS ON STRANDING USED IN AS22759 CONSTRUCTIONS. NAVAIR THEN CREATED MIL-W-29606 WHICH WAS INTENDED TO REPLACE THE ASTM SPECIFICATIONS AS THE REQUIRED CONDUCTOR SPECIFICATION. BEFORE THE MIL-W-29606 COULD BE ADDED TO MIL-W-22759, THE SPECIFICATION TRANSITION AND ADOPTION TOOK PLACE CONVERTING THE DOCUMENTS FROM MILITARY SPECIFICATIONS TO AS DOCUMENTS IN THE 1999 - 2000 TIME FRAME. SINCE THE EPL NO LONGER HAD LEGAL STANDING AFTER THE CONVERSION, WIRE PRODUCERS DID NOT HAVE TO ABIDE BY THE RESTRICTIONS WHICH ALLOWED THIS ISSUE TO CREEP BACK INTO THE 'PRODUCTS FROM TIME TO TIME. IN 2011, THE SAE AE-8D COMMITTEE OPENED A PROJECT TO UPDATE THE AS22759 AND ITS ASSOCIATED DETAILED SPECIFICATION SHEETS. WHEN LOOKING AT THIS ISSUE, THE COMMITTEE DECIDED TO ADOPT MIL-W-29606 (NOW AS29606) AND REPLACE THE ASTM REQUIREMENTS WITH THE AS29606 REQUIREMENTS. SINCE THE DIAMETER RANGE OF THE CONDUCTOR STRANDS NEEDED TO SHIFT SLIGHTLY TO THE RIGHT TO MEET THE NEW MINIMUM CMA REQUIREMENTS, OVERALL PRODUCT WEIGHT MAXIMUMS SHIFTED ABOUT 3 TO 5 PERCENT. THE COMMITTEE EVALUATED SEVERAL METHODS OF INCORPORATING THIS CHANGE INCLUDING CANCELING AND SUPERSESSION, BUT THE END USERS DID NOT WANT TO CHANGE PART NUMBERS FOR PRODUCTS WHICH HAVE BEEN USED IN AEROSPACE AND INDUSTRY FOR OVER 40 YEARS AND IS CURRENTLY ON THOUSANDS OF DRAWINGS. SINCE THESE PRODUCTS ARE PRIMARILY USED FOR PRIMARY POWER DISTRIBUTION FROM THE GENERATORS TO THE MAIN DISTRIBUTION PANELS, THE WEIGHT INCREASE TO THE ELECTRICAL INTERCONNECT SYSTEM IS CONSIDERED INSIGNIFICANT. SINCE THIS CHANGE DOES AFFECT THE MAXIMUM WEIGHT LIMITS FOR SIZES 8 THROUGH 4/0, END USERS SHOULD VERIFY THAT THE NEW WEIGHT RANGES MEET THE DESIGN REQUIREMENTS OF LEGACY APPLICATIONS. CORRECTED STATE OF SINTER REQUIREMENT.