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Product

MIL-DTL-55021 twisted pair & triplet avionics cableMIL-DTL-55021BTwisted Pair & TripletType I Unshielded / Type II Shielded

MIL-DTL-55021 Twisted Pair and Triplet Internal Aerospace Hook-UpMIL-DTL-55021B 600 V Type I unshielded & Type II shielded twisted pair and triplet

Precision-lay twisted-pair and twisted-triplet internal aerospace and defence hook-up cable (MIL-DTL-55021) built to MIL-DTL-55021B in Type I (unshielded, unjacketed) and Type II (85 % tinned/silver copper braid shielded, with optional jacket).

Low-EMC design
EMC screen
Flame-retardant
Approved
Order designation
M55021-T2J-2C22-81044
Configuration
Type II · 2 × 22 AWG Shld+Jkt
Max lay pitch
38.1 (1.50")
Nominal OD
2.98 mm
Weight
16.4 kg/km
All sizes (12)
Request a quoteDatasheetWhatsApp
Engineering reply in 2 business hoursCut-to-length export drumsEN 10204 3.1 certificate per drum
Voltage rating
600 Vrms
Up to 1,000 Vrms with Type C/E cores
Configurations
2C Pair / 3C Tri
Precision controlled twist pitch
Cable types
Type I & Type II
Unshielded (I) or ≥ 85 % Shielded (II)
Size range
30 AWG to 12 AWG
19-strand tinned or silver-plated Cu
Temperature
−65 to +200 °C
XL-PVDF (+150°C) or PTFE (+200°C)
Colour coding
White/Black/Red
MIL-DTL-55021 Table II standard

Typical values for this cable type, based on MIL-DTL-55021B (MIL-C-55021) / MIL-DTL-81044 / MIL-W-16878 — confirmed in the datasheet and quotation for your order.

Application fit

Is MIL-DTL-55021 right for your machine?

Designed for internal point-to-point wiring inside military LRU avionics black boxes, radar receivers, synchro/resolver loops, and differential RS-422/485 & LVDS telemetry.

Switchgear & control cabinet wiring

Suitable

Tight, uniform twist pitch (12–40 twists/ft) cancels magnetic-field pickup inside dense airborne LRU chassis.

Fixed installation

Suitable

Type II ≥ 85 % tinned or silver-plated copper braid isolates sensitive IF, synchro and transducer lines from switching noise.

Furnace, kiln & high-temp zone

Suitable

Available with M81044 (+150 °C) or MIL-W-16878 Type E/EE PTFE (+200 °C) primary cores for hot avionics bays.

Energy chain / drag chain

Not suitable

Intended for fixed internal equipment chassis and rack harnesses, not continuous drag-chain duty.

Use M81044
Typical machinesAirborne Line-Replaceable Unit (LRU) Avionics ChassisMilitary Radar, Electronic Warfare (EW) & Sonar RacksSynchro, Resolver, RVDT & LVDT Flight-Control LoopsDifferential RS-422 / RS-485, ARINC 429 & CAN Bus HarnessesMissile Guidance, Fire-Control & Telemetry Subsystems

Construction

Layer by layer

Representative Type II shielded build: 2 (pair) or 3 (triplet) × 26–16 AWG MIL-DTL-81044/12 (XL-polyalkene/PVDF) or MIL-W-16878/4 (PTFE) singles twisted with a left-hand lay (10–25 mm pitch) + ≥ 85 % coverage tinned or silver-plated copper braided shield + optional extruded XL-PVDF, FEP or PTFE outer jacket.

1234
Schematic, not to scale — generated from the layer data
#LayerMaterial & reference
119-strand tinned or silver-plated copper conductors (30–12 AWG)Concentric 19-strand (or 7-strand on 30–28 AWG) tinned copper (+150 °C) or silver-plated copper (+200 °C) per component wire specificationEnsures low contact resistance, high vibration fatigue life and compatibility with MIL-C-39029 crimp contacts
2Component primary insulation (M81044 XL-PVDF or MIL-W-16878 PTFE)Dual-wall radiation-crosslinked polyalkene/PVDF (M81044/12 or /9) or extruded fluoropolymer (PTFE/FEP/ETFE) primary cores colour-coded White/Black (Pair) or White/Black/Red (Triplet)Provides 600 Vrms dielectric isolation and balanced differential capacitance
3≥ 85 % tinned or silver-plated copper shield braid (Type II)Tightly woven 38–36 AWG tinned or silver-plated copper braid applied directly over the twisted pair or tripletProvides ≥ 60 dB electrostatic and RF shielding effectiveness across avionics frequency bands
4Optional thin-wall XL-PVDF, FEP or PTFE outer jacket (Type II Jacketed)Clear or white radiation-crosslinked PVDF, FEP or tape-sintered PTFE outer sheathPrevents shield-to-chassis ground loops and protects the braid against chafing inside card cages

MIL-DTL-55021 Type I (Unshielded Twisted Pair & Triplet)

Precision-twisted 2-core pair (White + Black) or 3-core triplet (White + Black + Red) for magnetic-loop cancellation inside shielded LRU boxes

MIL-DTL-55021 Type II (Braided Shielded, Unjacketed or Jacketed)

≥ 85 % tinned/silver copper braid over the twisted pair or triplet, supplied bare-braid (for grounded clamp routing) or with an insulating XL-PVDF/FEP jacket

Technical data

Ratings & operating limits

Typical values: Typical values for this cable type, based on MIL-DTL-55021B (MIL-C-55021) / MIL-DTL-81044 / MIL-W-16878. Values for your order are confirmed in the datasheet and quotation.

Electrical

Rated voltage
600 Vrms (with M81044 or MIL-W-16878 Type B/E cores) · 1,000 Vrms (Type C/EE)
Dielectric withstand
2.0 kVrms to 2.5 kVrms core-to-core & core-to-shield for 1 min
Shield coverage (Type II)
≥ 85 % optical braid coverage
Mutual capacitance (typical)
55 pF/m to 95 pF/m (unshielded) · 95 pF/m to 155 pF/m (shielded)

Thermal

Operating temp (M81044 cores)
−65 °C to +150 °C
Operating temp (PTFE cores)
−65 °C to +200 °C

Mechanical

Conductor sizes
30, 28, 26, 24, 22, 20, 18, 16, 14 & 12 AWG
Twist direction & pitch
Left-hand lay · 10 mm to 50 mm lay length per MIL-DTL-55021 Table I
Min. bend radius
4 × OD (Type I) · 6 × OD (Type II shielded)

Resistance

Fluid & chemical resistance
Resistant to aviation fuels, hydraulic fluids, cleaning solvents & fungus
Flammability
Self-extinguishing per MIL-DTL-55021 / SAE AS4373

Reference standards

Governing specification
MIL-DTL-55021B (supersedes MIL-C-55021A)
Permitted component wires
MIL-DTL-81044 · MIL-W-16878 · MIL-DTL-22759

Identification

Standard core colours
Pair: White + Black (or White + Striped) · Triplet: White + Black + Red
Customs tariff (HS)
8544.49

Sizes

12 standard MIL-DTL-55021 Type I & Type II twisted pair and triplet builds

Dimensions, twist lay pitch, shield configuration, finished OD and nominal weight using M81044/12 primary singles.

Type I / II, pair/triplet, AWG, lay pitch & OD
Order designationType, Cores & AWGPrimary Wire SpecMax Lay Pitch
mm (in.)		Nom. OD
mm		Max R20
Ω/km		Weight
kg/km		Enquiry
MIL-DTL-55021 Type I Unshielded Twisted Pairs (2C) & Triplets (3C)
M55021-T1-2C26-81044Type I · 2 × 26 AWG PairM81044/12-2625.4 (1.00")1.68139.53.7
M55021-T1-2C24-81044Type I · 2 × 24 AWG PairM81044/12-2431.8 (1.25")1.9488.65.5
M55021-T1-2C22-81044Type I · 2 × 22 AWG PairM81044/12-2238.1 (1.50")2.1854.78.0
M55021-T1-2C20-81044Type I · 2 × 20 AWG PairM81044/12-2044.5 (1.75")2.5433.012.0
M55021-T1-3C24-81044Type I · 3 × 24 AWG TripletM81044/12-2431.8 (1.25")2.0988.68.3
M55021-T1-3C22-81044Type I · 3 × 22 AWG TripletM81044/12-2238.1 (1.50")2.3554.712.0
MIL-DTL-55021 Type II Shielded & Jacketed Twisted Pairs (2CS) & Triplets (3CS)
M55021-T2J-2C26-81044Type II · 2 × 26 AWG Shld+JktM81044/12-2625.4 (1.00")2.45139.510.2
M55021-T2J-2C24-81044Type II · 2 × 24 AWG Shld+JktM81044/12-2431.8 (1.25")2.7288.612.8
M55021-T2J-2C22-81044Type II · 2 × 22 AWG Shld+JktM81044/12-2238.1 (1.50")2.9854.716.4
M55021-T2J-2C20-81044Type II · 2 × 20 AWG Shld+JktM81044/12-2044.5 (1.75")3.3833.022.1
M55021-T2J-3C24-81044Type II · 3 × 24 AWG Shld+JktM81044/12-2431.8 (1.25")2.9088.616.5
M55021-T2J-3C20-81044Type II · 3 × 20 AWG Shld+JktM81044/12-2044.5 (1.75")3.6033.029.5
  • Typical values for this cable type; dimensions and weights for your order are confirmed in the quotation.
  • Also supplied with MIL-W-16878/4 (Type E 600 V PTFE) or MIL-DTL-22759 primary singles and bare unjacketed braids per MIL-DTL-55021.

Quality & approvals

Testing & inspection

Routine tests on every production length, sample and type tests per batch — documented on an EN 10204 3.1 inspection certificate.

  1. ConductorClass 5 stranding
  2. Spark test100 % in-line
  3. Lay-upCores, earth, fillers
  4. SheathingInner, braid / screen, outer
  5. Electrical testsAC voltage, resistance
  6. DimensionsOD, wall thickness
  7. Inspection documents & dispatchDrum & dispatch
Testing & inspectionTest value / referenceFrequency
Routine tests
Dielectric withstand & spark test (core-to-core & core-to-shield)100 % spark test on primary cores and outer jacket + 2.0–2.5 kVrms dielectric proof test100 % of manufactured length
Twist lay length, lay direction & shield braid coverage (≥ 85 %)Verify left-hand lay pitch per Table I and optical braid angle/coverageEvery production spool
Sample tests
Cold bend (−65 °C), heat aging (+150/+200 °C) & flammabilityConfirm zero cracking and self-extinguishing behaviour after thermal conditioningLot qualification

Inspection certificate

Issued with every drum, listing the routine test results for that length.

Product approvals

MIL-DTL-55021B (MIL-C-55021) Type I & Type II CompliantSAE AS81044 & MIL-W-16878 Qualified Component Cores

Company certificates

ISO 9001ISO 14001ISO 45001VDE marks approvalUL / cULCE · LVD / EMC

Marking & supply

Ordering & delivery

Sheath marking

MIL-DTL-55021B Colour-Coded Cores (White/Black + Red) & Spool Traceability Tag
Delivery form
500 ft & 1,000 ft spools with MIL-DTL-55021B Certificate of Conformance
Custom twisting
Custom twist pitches (up to 40 twists/ft) & MIL-STD-681 striped colour combinations
Lead time
2–3 weeks ex-works

Technical documents

Downloads

PDFMIL-DTL-55021 Twisted Pair and Triplet Internal Aerospace Hook-Up – technical datasheet12 sizes · construction, technical data, approvalsXLSXMIL-DTL-55021 spec data (Excel)All 12 sizes with dimensions and data, for your BOM or quotation
Revision
2026-10-20
Updated
2026-10-20

FAQ

Questions engineers ask first

Not covered here? Send your drawing — an engineer replies within 2 business hours.

What is the difference between MIL-DTL-55021 and NEMA WC 27500 (MIL-DTL-27500)?
MIL-DTL-55021 specifically covers small-gauge internal equipment hook-up twisted pairs (2C) and triplets (3C)—either unshielded (Type I) or shielded (Type II)—for wiring inside avionics LRU enclosures and electronics racks. NEMA WC 27500 (MIL-DTL-27500) covers external airframe inter-bay harness cables from 1 to 15+ conductors with a structured part-number matrix for 14 different shield and jacket materials.
Why are twisted triplets (3 conductors) specified alongside twisted pairs in MIL-DTL-55021?
Avionics synchros, 3-wire RTDs, resolvers, and 3-phase 400 Hz reference transformers require three phase-balanced conductors routed through the exact same magnetic path so that external 400 Hz magnetic fields induce equal common-mode voltages on all three wires, preventing angular position error.
Should I specify Type II Shielded with or without an outer insulating jacket?
Original MIL-C-55021 Type II included bare-braid shielded pairs so the outer braid could be grounded at multiple chassis clamps. However, inside modern printed-circuit card cages, an uninsulated braid risks shorting against PCB pins and creates multipoint ground loops—so Type II with a thin XL-PVDF, FEP or PTFE outer jacket is strongly preferred.
Why does MIL-DTL-55021 enforce a strict maximum twist lay length in Table I?
Magnetic-field rejection (common-mode noise cancellation) is inversely proportional to the area of each twist loop. By keeping the lay length short and uniform (e.g. ≤ 25.4 mm on 26 AWG, ≤ 38.1 mm on 22 AWG), adjacent half-twists expose equal and opposite loop areas to stray magnetic fields.

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