Key takeaways
- A braid is defined by carriers, ends per carrier, wire diameter and picks per unit length.
- Copper area is a calculation from those numbers; ampacity needs a derating for weave, termination and mounting.
- Fine wire and a long lay give flexibility; more picks and thicker wire give coverage and abrasion resistance.
- Coverage describes how much of the surface is covered, not how much copper is inside.
What the construction numbers describe
A braid is not described by a single size in the way a cable is. It is described by how many carriers the machine runs, how many wire ends each carrier supplies, the diameter of each wire, and how tightly the weave is closed. Change any one of those and the copper area, the flexibility and the surface all move.
The carrier is the spool position on the braiding machine. Each carrier feeds a group of wires, called an end. The ends from opposing carriers interlace in a maypole pattern, and the take-off speed relative to the carrier speed sets the braid angle and the picks per unit length.
A flat braid is woven over a flat mandrel or flattened after weaving, so it sits against a pad or a bar. A tubular braid keeps a round section and is used where the movement comes from several directions. The same carrier count can produce either, but the flat form has a wider envelope.
Reading a braid specification
Braids are often written as three numbers, for example 24 x 8 x 0.20, meaning 24 carriers, 8 ends per carrier and 0.20 mm wire. That is a useful shorthand, but it is not a complete specification, because it says nothing about the lay, the braid angle, the flat width or the termination.
The wire count follows directly: 24 multiplied by 8 gives 192 wires. The copper area is the wire count multiplied by the area of one wire. For 0.20 mm wire the area of one wire is about 0.0314 mm², so the total is about 6.0 mm². That number is the copper, not the space the braid occupies.
The envelope is larger. A braid of 6.0 mm² copper might sit in a flat section of 10 mm by 1.5 mm, or about 15 mm² of space, because the weave is mostly air. The difference between copper area and envelope area is the fill factor, which decides whether the link fits.
Write the full construction, not just the area
A 6 mm² braid can be made from thick wire in a loose weave or fine wire in a tight weave. The two behave differently in flex and in current. The drawing should state carriers, ends, wire diameter and lay.
Coverage and what it does not tell you
Coverage is the proportion of the braid surface that the wires cover when the braid is viewed from outside. It rises with more picks per unit length, thicker wire and a steeper braid angle. A tight weave approaches full coverage; a loose weave leaves visible gaps.
Coverage is useful for abrasion and appearance, and for keeping a sleeve or potting compound in place. It is not a measure of copper area. A braid can have high coverage with fine wire and a modest copper section, or low coverage with thicker wire and more copper.
The lay length is the distance along the braid for one full revolution of a carrier. A short lay gives a tight, dense weave with a steep braid angle. A long lay gives a more open weave with a shallower angle and more room for the strands to move. That is the main lever on flexibility after wire diameter.
From copper area to ampacity
A first estimate of current capacity starts from copper area and a current density. For illustration, a braid with 6.0 mm² of copper at 2 A/mm² would be described as about 12 A. That is a comparison figure, not a rating. The density that is safe depends on the ambient, the enclosure, the termination and the allowable temperature rise.
The weave reduces the effective conductivity. Strand to strand contact is a set of small contact points, the current path is longer than the straight length, and sharing between carriers is uneven near the ends. A braid therefore runs warmer than a solid conductor of the same copper area, and a derating factor of the order of 15 to 25 per cent is common for free-air ratings, depending on the construction.
Inside an enclosure the local ambient can be much higher than the room. A rating quoted in free air does not transfer into a cabinet with other heat sources. Ask for the rating basis: ambient, mounting, sleeve, termination and permitted temperature rise.
| Construction | Wires | Copper area | Illustrative current at 2 A/mm² | Relative flexibility |
|---|---|---|---|---|
| 16 x 6 x 0.15 | 96 | 1.7 mm² | 3.4 A | High |
| 24 x 8 x 0.20 | 192 | 6.0 mm² | 12.1 A | Medium |
| 24 x 10 x 0.20 | 240 | 7.5 mm² | 15.1 A | Medium |
| 32 x 10 x 0.20 | 320 | 10.0 mm² | 20.1 A | Low to medium |
Illustrative only. The 2 A/mm² figure is a comparison placeholder, not a safe rating. Real ampacity depends on weave, termination, ambient, sleeve and mounting.
Construction and flexibility
Wire diameter is the strongest influence on flex life. A braid made from 0.10 mm wire bends more easily and lasts longer in a tight radius than one made from 0.30 mm wire with the same copper area. The finer wires cost more to draw and to braid, and they are more easily damaged by a rough ferrule.
Lay length is the second influence. A long lay lets the strands move along each other as the braid bends, which spreads the strain. A short lay locks the strands together, which makes the braid stiffer and more abrasion resistant but less tolerant of repeated flex.
The third influence is the termination. A ferrule that crushes the weave into a hard step creates a stress concentration right where the strands stop moving. A gradual transition, a support sleeve or a strain relief boot can add more life than a change of weave.
What to put on the drawing and the RFQ
State the construction in full: carriers, ends per carrier, wire diameter, flat or tubular, lay length or picks, and the nominal flat width and thickness. Add the copper area as a derived check, not as the only callout, so the supplier cannot meet the area with a construction that will not flex.
Add the termination: ferrule or weld, pad size, hole pattern, plating and the length of the consolidated end. State the current, the ambient, the movement and the test. If the braid will be sleeved, say so, because the sleeve changes the thermal rating.
A braid drawing without a lay and a termination length leaves the two most important life variables to the supplier. Those are exactly the variables that will differ between quotes, and the reason two prices for the same copper area can be far apart.
- Carriers, ends per carrier and wire diameter
- Flat or tubular, with nominal width and thickness
- Lay length or picks per unit length
- Copper area as a derived value
- Termination type, pad geometry and plating
- Current, ambient duty and movement
- Sleeve, test and marking requirements
Incoming inspection of a braid
The first check is construction. Count the carriers and the ends, measure the wire diameter on a sample of strands, and confirm the flat width. A braid with the right copper area but the wrong wire diameter will pass a resistance check and fail in flex.
The second check is electrical. A resistance per metre measurement on a known length, compared with the calculated value for the copper area, catches missing ends and poor strand contact. A millivolt drop test across a terminated sample catches a bad ferrule or weld.
The third check is visual and dimensional. Look for broken strands, loose ends, a weld that has not captured the full width, and a flat section that has been crushed in packing. Record the results against the lot, because a braid failure is usually traced back to a construction change rather than to the copper itself.
Frequently asked questions
How is copper braid area calculated?
Multiply the number of carriers by the ends per carrier to get the wire count, then multiply by the area of one wire. For 0.20 mm wire the area is about 0.0314 mm². A 24 x 8 x 0.20 braid therefore has 192 wires and about 6.0 mm² of copper.
Does higher coverage mean more current capacity?
Not directly. Coverage describes the surface, while capacity depends on copper area, strand contact, termination and cooling. A tight weave can have high coverage and less copper than a loose weave of thicker wire.
What wire diameter should a flexible braid use?
Finer wire gives better flex life for the same copper area, at a higher cost and with more risk of damage at the termination. The choice depends on the bend radius and the cycle count, not on current alone.
Why is a braid rated lower than a solid bar of the same area?
The weave has a longer current path, contact resistance between strands and uneven sharing between carriers. It also traps heat. A derating is applied to the solid conductor figure for the actual construction and mounting.
Sources and further reading
- ASTM B3, Standard Specification for Soft or Annealed Copper Wire
- IEC 60228, Conductors of insulated cables
- Qumek braid construction and current rating review notes
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