Choosing the Wire: Solid or Stranded, and What the Gauge Number Means

SOLID core is one thick conductor. It holds its shape, pushes into a breadboard neatly, and is what house wiring uses — because house wiring never moves. STRANDED is many fine conductors twisted together. Each strand bends through a much smaller radius than one thick wire would, so the bundle flexes without fatiguing. Anything on a door, a lid, a robot arm or a lead that gets coiled up must be stranded. The failure is specific and worth recognising: a solid wire that has been flexed repeatedly breaks INSIDE the insulation, so the joint looks perfect and the circuit is open. The published fault-finding rung is where that gets diagnosed; choosing stranded is where it gets avoided.

In AWG, a BIGGER number is a THINNER wire. 30 AWG is hair-fine wire-wrap; 22 AWG is typical hookup wire; 14 AWG is a mains circuit; 4 AWG is a car battery lead. The scale is logarithmic and there is one number worth memorising: every THREE gauges roughly doubles or halves the cross-sectional area. So 16 AWG has about twice the copper of 19 AWG and about half of 13 AWG, and you can estimate the rest from any gauge you know. Metric wire is sized directly by cross-section in square millimetres — 0.5 mm², 1.5 mm², 2.5 mm² — which is less confusing and increasingly common. The notebook step converts between them.

Insulation has a temperature rating and a voltage rating. PVC is the default and softens near a soldering iron; silicone stays flexible and tolerates heat, which is why it is worth the cost for anything near a hot part. Colour carries no electrical meaning at all — it is purely a convention, and its whole value is that you keep it. Red for positive and black for negative in DC work is nearly universal and costs nothing to follow. Inventing your own scheme is fine; changing it halfway through a project is not. Where a wire's colour cannot be chosen, label it. A strip of tape with a number at each end of a long run saves far more time later than it costs now, and it is what turns a bundle of identical black wires from a puzzle into a harness.