Bare Copper Wire in E.C. Grade, by SWG or Millimetre

• Size: diameter in millimetres, or a gauge number with the gauge system named (SWG and AWG numbers do not match)
• Temper: hard drawn for strength and straightness, soft annealed for bending, winding and crimping
• Finish: bare, tinned or nickel-plated
• Quantity and packing: total kilograms and the coil or spool weight your machine or crew can handle

India still uses the British Standard Wire Gauge (SWG) widely for bare copper wire, especially for earthing and electrical contracting. American Wire Gauge (AWG) appears on imported equipment and in ASTM standards, and the metric diameter is used in IS specifications and most modern drawings. The numbers look similar but the sizes are not: 14 SWG is 2.032 mm, while 14 AWG is about 1.63 mm. When in doubt, give us the diameter in millimetres and we will work from that.

The chart below gives common SWG sizes with cross-section and theoretical weight. Earthing specifications usually state a cross-section in mm², so the area column is the one to check against a drawing. For lightning protection, IS/IEC 62305 sets 50 mm² as the usual minimum for copper conductors, which is larger than any size in this chart.

Hard drawn copper wire (ASTM B1) is stiff and strong, roughly 340–460 MPa depending on size, and keeps about 96–97 % IACS. It is the choice for bare overhead conductors, exposed earth runs that must stay straight between clips, and lightning down conductors.

Soft annealed copper wire (ASTM B3) has full 100 % IACS and high elongation. It is used for windings, stranding into flexible conductors, binding and lashing, jumpers, buried earth conductors, and anything formed by hand. Indian general engineering wire is covered by IS 4412, and conductors for insulated cables by IS 8130.

Tinned wire to ASTM B33 is the standard choice for marine, coastal and sulphur-laden environments and anywhere the wire will be soldered. Nickel-coated wire to ASTM B355 is for higher temperatures, typically PTFE-insulated wire and furnace leads. Both are normally drawn on soft annealed base wire. Our tinned copper page compares the coatings.

In the trade, bare copper wire is priced per kilogram and supplied in coils. To convert between length and weight, use: kg per km = diameter (mm) × diameter (mm) × 6.99. So 100 m of 3 mm wire weighs 3 × 3 × 6.99 ÷ 10 = about 6.3 kg. If a crew needs a specific length, tell us the length and we will work out the weight, or vice versa.

Coil weight matters on site. A heavy coil of hard drawn wire is awkward to pay out on a roof, while light coils of fine wire tangle easily. Say how the wire will be handled and we can suggest a sensible coil size.

Many earthing layouts use both. Copper strip, such as 25 × 3 mm, is common for main earth conductors and ring mains because a flat section has more surface area for its weight, sits neatly on walls and cable trays, and bolts easily to earth bars. Round wire is usually chosen for branch connections to equipment, for bonding, and for runs that have to bend around obstacles. If the design gives only a cross-section in mm², either form can meet it, so the choice comes down to routing and termination. We supply both, so a single enquiry can cover the whole earthing schedule.

A micrometer on a few points along the coil confirms diameter; out-of-round wire suggests poor drawing. A hand bend tells soft from hard. For conductivity, a resistance check on a measured length against the IACS value, corrected to 20 °C, is the real test, and the test certificate should report it for electrical work. Bright, uniform colour with no black streaks or slivers is a good first sign of clean drawing.