Engineering Specification Guide: Base Wires, Shielding, Jackets, & Thermal Limits
1. Series Overview & Aerospace Application Scope
The M27500 / NEMA WC 27500 specification defines the technical construction and performance criteria for high-reliability special purpose and power cables engineered specifically for military, aerospace, avionics, and airframe applications. These multi-conductor cables are constructed using 1 to 15 inner conductors and accommodate a wide spectrum of conductor gauges, primary insulation materials, metallic shielding configurations, and high-temperature protective jacket compounds. Although the finished cable assembly does not require a Qualified Products List (QPL) qualification in itself, all internal base wires must originate from QPL-qualified sources under their respective military basic wire specifications.
Designed to maintain electrical integrity under severe environmental stress, M27500 cables offer continuous operating temperature capabilities ranging from -55°C up to +400°C depending on the selection of base wire insulations (e.g., Cross-Linked ETFE, PTFE, Polyimide) and shielding/jacket materials.
2. Part Number Anatomy Structure
Every military part callout in this specification consists of up to 16 characters following a rigid nomenclature format (e.g., M27500-20SB3T23 or M27500A20JA4C09):
| Component Callout | Example Code | Description & Standard Reference |
| Specification Callout | M27500 | Mandatory specification series callout identifier. |
| Color Code & Shield Coverage | – | Identifies 85% shield coverage with preferred colored stripes on white wire. |
| Conductor Size (AWG) | 20 | Identifies the wire gauge size (e.g., 20 AWG). |
| Base Wire Spec Symbol | SB | SAE AS22759/32 basic component wire (Cross-Linked ETFE). |
| Number of Conductors | 3 | Defines total count of internal conductors (1 to 15). |
| Shield Type & Material | T | Single Tin-Plated Copper (TPC) round braid shield (Max 150°C). |
| Jacket Compound | 23 | Single extruded White Modified Cross-Linked ETFE jacket (Max 200°C). |
3. Master Component Reference Tables
Table 1: Base Component Wire Specifications & Thermal Ratings (Table B Excerpt)
| Symbol | Base Wire Spec | Primary Insulation Compound | Temp Rating | Voltage |
| A / B | SAE AS5086/1, /2 | PVC / Nylon / Glass Braids | 105°C / 90°C | 600V |
| RC / RE | SAE AS22759/11, /12 | Extruded PTFE (Silver / Nickel Plated) | 200°C / 260°C | 600V |
| CA / CB / CC | SAE AS22759/13, /14, /15 | Fluoropolymer / Polyimide Tape | 150°C / 200°C | 600V |
| TE / TF / TG / TH | SAE AS22759/16, /17, /18, /19 | Extruded ETFE Fluoropolymer | 150°C | 600V |
| SB / SC / SD / SE | SAE AS22759/32, /33, /34, /35 | Cross-Linked ETFE (XL-ETFE) | 150°C / 200°C | 600V |
| SM / SN / SP / SR | SAE AS22759/41, /42, /43, /44 | Dual-Wall Cross-Linked ETFE | 150°C / 200°C | 600V |
| MD / ME / MF / MG | SAE AS81044/5, /6, /7, /8 | XL-Polyalkene / PVDF Dual Wall | 150°C | 600V |
| MR / MS / MT / MV | SAE AS81381/7, /8, /9, /10 | Polyimide (Kapton) Tape Wrapped | 200°C | 600V |
| JA / JF | SAE AS25038/1, /3 | Quartz / PTFE Heavy Duty Fire Resistant | 400°C | 600V |
Table 2: Cable Shielding Styles, Materials, & Thermal Limits (Table C Excerpt)
| Single | Double | Shield Material & Geometry | Braid Geometry | Max Temp |
| U | — | No Shield (Unshielded Construction) | N/A | N/A |
| T | V | Tin-Plated Copper (TPC) | Round Braid | 150°C |
| S | W | Silver-Plated Copper (SPC) | Round Braid | 200°C |
| N | Y | Nickel-Plated Copper (NPC) | Round Braid | 260°C |
| F | Z | Stainless Steel | Round Braid | 400°C |
| C | R | Nickel-Clad Copper (27% Heavy NPC) | Round Braid | 400°C |
| M | K | Silver-Plated High Strength Copper Alloy | Round Braid | 200°C |
| P | L | Nickel-Plated High Strength Copper Alloy | Round Braid | 260°C |
| G | A | Silver-Plated Copper (SPC) | Flat Braid | 200°C |
| H | B | Silver-Plated High Strength Copper Alloy | Flat Braid | 200°C |
| J | D | Tin-Plated Copper (TPC) | Flat Braid | 150°C |
| I | Q | Nickel-Chromium Alloy | Flat Braid | 400°C |
Table 3: Protective Outer Jacket Compounds & Operating Temperatures (Table D Excerpt)
| Single | Double | Outer Jacket Material Compound | Max Temperature |
| 00 | 00 | No Outer Protective Jacket | N/A |
| 01 / 02 | 51 / 52 | Extruded White PVC / Extruded Clear Polyamide (Nylon) | 90°C / 105°C |
| 05 / 09 | 55 / 59 | Extruded Clear FEP / Extruded White FEP Fluoropolymer | 200°C |
| 06 | 56 | Extruded or Taped White PTFE | 260°C |
| 07 | 57 | White Glass Braid PTFE Over PTFE Tape | 260°C |
| 08 / 10 | 58 / 60 | Cross-Linked White PVDF / Extruded Clear PVDF | 150°C / 125°C |
| 11 / 12 | 61 / 62 | Polyimide Over FEP Wrapped Polyimide Tape | 200°C |
| 14 / 15 | 64 / 65 | Extruded White ETFE / Extruded Clear ETFE | 150°C |
| 20 / 21 | 70 / 71 | Extruded White PFA / Extruded Clear PFA | 260°C |
| 23 | 73 | Extruded White Modified Cross-Linked ETFE (XL-ETFE) | 200°C |
Table 4: Color Identification & Shield Coverage Methodologies (Table A Excerpt)
| 85% Coverage | 90% Coverage | Identification System Description | Color Marking Method |
| – | C | Preferred Method (Table A-1) | Colored Stripes on White Base Wire |
| A | D | Optional Method A (Table A-1) | Solid Color Base Wires |
| B | E | Optional Method B (Table A-3 / A-4) | Band Marking (Wire Numbers) on Solid Colors by AWG |
| F | H | Preferred Method Alternate (Table A-2) | Colored Stripes on White Base Wire (Alternate Sequence) |
| G | J | Optional Method A Alternate (Table A-2) | Solid Color Wires (Alternate Sequence) |
| K | M | Optional Method C (Table A-3) | Printed Number Marking on Solid Color Wires by AWG |
| L | N | Optional Method D | Printed Number Marking on White Wires |