Tubular braid on cable
Braided directly over the insulated core during cable manufacture. Used in coaxial, data, instrumentation and EV high-voltage cables.
EMI / RFI cable shielding
Braided Shielding Wire for Cable EMI Protection
Braided shielding wire is fine wire, usually 0.10 – 0.25 mm, woven into a tube or flat strap around a cable core to block electromagnetic interference and carry fault or drain current. The choice of wire metal, plating and braid coverage decides how well the shield works, how much it weighs and how long it lasts. Metline supplies braid wire and finished braids in aluminium, aluminium-magnesium alloy and copper-clad aluminium to cable makers worldwide; copper braids are described here for comparison.
- Wire size
- 0.10 – 0.25 mm (≈ 38 – 30 AWG)
- Coverage
- 70 – 95 % optical
- Metals
- 1350 Al, Al-Mg, CCA
- Forms
- Tubular, flat, expandable
How a braided shield works
A braid is formed on a braiding machine where carriers, each holding a bobbin of several parallel wires, travel in opposite directions around the cable and interlace the wires in an over-under pattern. The result is a flexible metal sleeve that surrounds the conductors and connects to ground at the cable ends.
The shield works in two ways. Incoming electromagnetic fields induce currents in the braid that are drained to ground instead of reaching the signal conductors, and fields generated by the cable itself are contained in the same way. At low and medium frequencies a braid is very effective because its low DC resistance carries induced currents well. At high frequencies energy leaks through the small openings in the weave, which is why many cables combine a braid with an aluminium foil tape underneath.
Engineers rate shields by transfer impedance (how much voltage appears on the inner conductors per ampere of current on the shield, per metre) and by shielding attenuation in decibels. Both improve with higher coverage, lower-resistance wire, a second braid layer and a foil-plus-braid combination.
Types of braided shielding and sleeving
Braided sleeving
A loose tubular braid supplied on reels and slid over harnesses afterwards. Expands to pass connectors, then contracts to fit the bundle.
Flat braid and grounding strap
Braid flattened into a strap, often fitted with crimped or pressed terminals, used for equipment bonding and flexible earthing.
High-coverage braid
Smaller wire, more ends per carrier and a lower braid angle push optical coverage above 90 % for sensitive signals.
Double braid
Two braid layers, sometimes separated by a foil or film, for much lower transfer impedance in military, aerospace and test cables.
Hybrid braid
Mixes aluminium alloy and tinned copper wire on the same machine to reduce weight while keeping solderable copper strands.
Braid wire materials compared
Most braids are made from copper, plain or plated, or from aluminium and aluminium alloys. Conductivity values below are typical approximations for the wire metal.
| Wire | Typical conductivity | Density | Strengths | Limitations | Typical use |
|---|---|---|---|---|---|
| Bare annealed copper | 100 % IACS | 8.89 g/cm³ | Lowest resistance, durable | Tarnishes in humidity, heavy | Indoor signal and instrumentation cables |
| Tinned copper | about 97 – 99 % IACS | 8.89 g/cm³ | Solderable, corrosion resistant | Heavy, tin limits temperature to about 150 °C | Automotive, industrial, telecom |
| Silver-plated copper | ≥ 100 % IACS | 8.9 g/cm³ | High-frequency skin conduction, 200 °C class | Cost | Aerospace, RF and microwave |
| Nickel-plated copper | about 90 – 95 % IACS | 8.9 g/cm³ | Oxidation resistance at high temperature | Lower conductivity, harder to solder | Aerospace, high-temperature zones |
| 1350 aluminium | about 61 % IACS | 2.70 g/cm³ | Light, good conductivity per kilogram | Low strength for fine wire | Heavier gauge braids and straps |
| Al-Mg alloy (about 3 – 4 % Mg, e.g. 5154 type) | about 30 – 35 % IACS | 2.66 g/cm³ | Strong enough to braid fine, corrosion resistant, light | Higher resistance; not solderable | Coaxial (CATV) cable braids, light harnesses |
| Copper-clad aluminium (CCA) | about 63 – 65 % IACS | 3.3 – 3.6 g/cm³ | Copper surface, low weight and cost | Lower flex-life than copper | Data and coaxial cable braids |
| Stainless steel | about 2 – 3 % IACS | 7.9 g/cm³ | Abrasion and crush protection | Poor shield on its own | Rugged mechanical overbraids |
Silver plating, nickel plating and tin coating of copper wire are covered by ASTM B298, B355 and B33 respectively; CCA wire by ASTM B566.
Strand sizes, resistance and weight
The braid wire diameter sets coverage, flexibility and resistance. The table gives calculated DC resistance and mass per metre of a single strand at 20 °C. Resistivity used: annealed copper 0.01724, 1350 aluminium 0.02826 and Al-Mg braid alloy about 0.052 Ω·mm²/m.
| Diameter (mm) | Approx. AWG | Area (mm²) | Cu (Ω/m) | 1350 Al (Ω/m) | Al-Mg (Ω/m) | Cu mass (g/m) | Al mass (g/m) |
|---|---|---|---|---|---|---|---|
| 0.10 | ≈ 38 | 0.0079 | 2.20 | 3.60 | 6.62 | 0.070 | 0.021 |
| 0.12 | ≈ 36–37 | 0.0113 | 1.52 | 2.50 | 4.60 | 0.101 | 0.031 |
| 0.16 | ≈ 34 | 0.0201 | 0.86 | 1.41 | 2.59 | 0.179 | 0.054 |
| 0.20 | ≈ 32 | 0.0314 | 0.55 | 0.90 | 1.66 | 0.279 | 0.085 |
| 0.25 | ≈ 30 | 0.0491 | 0.35 | 0.58 | 1.06 | 0.436 | 0.133 |
Al-Mg braid wire is normally supplied hard-drawn for strength on the braiding machine, or annealed for higher elongation where the cable flexes. Typical minimum tensile strength for hard Al-Mg braid wire in these sizes is about 300 MPa, and around 220 – 230 MPa when annealed; confirm the exact limits on the mill certificate. Copper braid wire is almost always soft annealed.
A braid made from aluminium alloy weighs roughly 30 % of an equivalent copper braid, which is why coaxial cable for cable TV and satellite almost always uses an Al-Mg braid over a bonded aluminium foil.
Braid coverage and how it is calculated
Optical coverage is the percentage of the cable surface hidden by metal. It is calculated from the number of carriers (C), ends per carrier (N), wire diameter (d), picks per unit length (P) and the core diameter under the braid (D):
- Braid angle αtan α = 2π (D + 2d) P / C
- Fill factor FF = N · P · d / sin α
- Coverage KK = (2F − F²) × 100 %
| Coverage | Typical character | Typical use |
|---|---|---|
| 60 – 70 % | Light, flexible, lowest cost | CATV coax braid over foil, general harness sleeving |
| 80 – 85 % | Balanced shielding and flexibility | Industrial control, automotive and marine cables |
| 90 – 95 % | High shielding, stiffer, heavier | Data, instrumentation, aerospace and defence |
| Double braid or braid + foil | Lowest transfer impedance | Test leads, military, broadcast and EV HV cables |
Raising coverage beyond about 95 % adds weight and stiffness for small gains. Braid angle matters too: angles between about 30° and 45° are common; a lower angle gives better flexibility and lower transfer impedance at high frequency, a higher angle better crush resistance.
Foil vs braid, and copper vs aluminium braid
| Shield | Advantages | Limitations | Typical use |
|---|---|---|---|
| Aluminium foil tape | Close to 100 % coverage, light, low cost, excellent at high frequency | Poor flex-life, high DC resistance, needs a drain wire | LAN, USB and HDMI pairs, instrumentation |
| Braid | Low DC resistance, flexible, strong, easy to terminate | Coverage below 100 %, heavier | Industrial, automotive, aerospace, power cables |
| Foil + braid | Combines high-frequency and low-frequency shielding | Cost and diameter | Coaxial, EV HV cables, critical data links |
Copper braid gives the lowest resistance and best solderability and remains the default for aerospace and military cables. Aluminium and Al-Mg braids cut braid weight by around two-thirds and cost less; they are terminated by crimping or clamping rather than soldering. CCA braid sits between the two and can be soldered thanks to its copper skin.
Where braided shielding wire is used
- Coaxial and broadband cable: Al-Mg or CCA braid over bonded foil for CATV, satellite and antenna feeds
- Data and communication: industrial Ethernet, fieldbus, USB and multi-core signal cables
- Automotive and EV: high-voltage cables between battery, inverter and motor, where shields contain switching noise; aluminium braids save weight
- Industrial control: VFD motor cables, robot and drag-chain cables
- Aerospace and defence: silver- or nickel-plated copper braids and sleeving for avionics harnesses
- Marine and offshore: tinned copper or aluminium alloy braids that resist salt atmosphere
- Medical and audio: fine copper braids in patient leads, microphone and instrument cables
- Grounding and bonding: flat braids linking doors, frames and equipment to earth
Termination and common specification mistakes
A shield is only as good as its connection to ground. A braid with 95 % coverage that is terminated by a long twisted pigtail can perform worse than a 70 % braid clamped 360° around a connector backshell, because the pigtail adds inductance that dominates at high frequency.
- Terminate 360°: use backshells, crimp ferrules or EMC cable glands that clamp the whole braid circumference
- Match the metal to the termination: do not specify aluminium braid where the assembly line solders shields
- Avoid galvanic pairs in wet areas: aluminium braid against bare copper connectors needs plating or sealing
- Specify coverage and angle, not only "braided": two braids of the same wire can differ by 20 % in coverage
- Check flex requirements: drag-chain and robot cables need annealed wire, a low braid angle and flex testing
- Ask for resistivity on the certificate: for Al-Mg wire it varies with magnesium content and temper
Standards for braid wire and shield performance
| Standard | Covers |
|---|---|
| ASTM B3 / ASTM B33 | Soft annealed copper wire / tinned soft copper wire |
| ASTM B298 / ASTM B355 | Silver-coated / nickel-coated soft copper wire |
| ASTM B566 | Copper-clad aluminium wire |
| IEC 62153-4 series | Test methods for transfer impedance and screening attenuation of cables |
| MIL-DTL-17 | Coaxial RF cables, including braid requirements |
| RoHS / REACH | Restricted substances in plated wire for EU markets |
For Al-Mg braid wire there is no single international product standard; cable makers specify diameter tolerance, tensile strength, elongation and resistivity on their purchase specifications, and the mill certificate reports each one.
Supply range and how to order
Supply range
- Braid wire
- 0.10 – 0.25 mm, hard or annealed, on spools or bobbins ready for braiding machines
- Wire metals
- Al-Mg alloy, 1350 aluminium and copper-clad aluminium (CCA), bare or tinned
- Finished braid
- Tubular braid and sleeving about 2.5 – 38 mm, flat braid and grounding straps
- Coverage
- About 70 – 95 % single braid; double braid on request
- Packing
- Spools, reels or cut lengths, labelled by lot
- Documents
- Certificate with diameter, tensile, elongation and resistance results
- SpecifyWire metal (Al-Mg, 1350 or CCA) and any tinning, diameter and tolerance, temper, spool type, or braid diameter, coverage and construction.
- SampleTrial spools or braid samples can be arranged for machine and shielding tests.
- ConfirmWe confirm specification, test plan and delivery terms (EXW, FOB, CIF or DAP).
- ShipSpools packed in cartons on pallets, sealed against moisture for sea freight.
References and standards
- ASTM B33 – Tin-Coated Soft or Annealed Copper Wire for Electrical Purposes
- ASTM B355 – Nickel-Coated Soft or Annealed Copper Wire
- ASTM B566 – Copper-Clad Aluminum Wire
- IEC 62153-4 – Metallic communication cable test methods: electromagnetic compatibility (transfer impedance, screening attenuation)
- MIL-DTL-17 – Cables, Radio Frequency, Flexible and Semirigid
Braided shielding wire: frequently asked questions
Is aluminium braid as good as copper braid for shielding?
Not quite at equal construction, because aluminium alloy wire has higher resistance. But an Al-Mg braid over a bonded aluminium foil gives the shielding needed for coaxial and many data cables at about a third of the braid weight, and that is why it dominates CATV cable.
What braid coverage do I need?
Around 60 – 70 % is common where a foil does most of the high-frequency work; 80 – 85 % suits general industrial and automotive cables; 90 – 95 % or a double braid is used for sensitive, aerospace and military applications.
What wire diameter is used for braided shields?
Most braids use 0.10 – 0.25 mm wire (about 38 – 30 AWG). Finer wire gives higher coverage and flexibility on small cables; thicker wire gives strength and lower resistance on large cables and grounding straps.
Can aluminium braid be soldered?
Plain aluminium and Al-Mg braids cannot be soldered with normal methods; they are terminated by crimp ferrules or clamping connectors. If soldering is required, CCA braid is the aluminium-based option, because its copper skin takes solder; tinned copper braid is the all-copper alternative.
When should I choose nickel- or silver-plated copper braid?
Choose silver-plated for RF and high-temperature service up to about 200 °C, and nickel-plated where oxidation at even higher temperature is the concern. Tinned copper is limited to about 150 °C.
Do you ship braid wire internationally?
Yes. Metline supplies aluminium, Al-Mg and CCA braid wire and finished braids worldwide on spools, reels or cut lengths with lot certificates.
Specifying a cable shield?
Send your wire metal, diameter, coverage and quantity. We will reply with a construction proposal and delivered price.
