Stranded or solid wire - which conductor fits when?

How do stranded and solid conductors differ?

A solid conductor is a single continuous wire, while a stranded conductor is made of many thin wires twisted together. IEC 60228 (mirrored by DIN VDE 0295) sorts conductors into classes 1 to 6: class 1 is the single solid wire, class 2 the standard multi-wire conductor, and classes 5 and 6 are fine and extra-fine flexible strands.

The higher the class, the more numerous and thinner the individual wires and the more flexible the conductor. The very same cross-section, for example 1.5 mm², can be supplied as a stiff class 1 solid wire or as a highly flexible class 6 strand with hundreds of individual wires.

What about flex-life and routing?

For repeated movement the stranded conductor is clearly superior. Because the stress is shared across many thin wires, a fine class 6 strand survives tens of thousands to millions of bending cycles in drag chains and on robots, whereas a solid wire work-hardens and breaks after only a few flexes.

• Stranded (cl. 5/6): ideal for moving, dragged and frequently re-plugged connections.
• Solid (cl. 1): ideal for a one-time routed, then static installation.
• Mind the bend radius: flexible strands allow much tighter radii than solid wire.
• For drag chains use dedicated continuous-flex strands, not standard connecting leads.
• Solid wire can be shaped and holds its position, an advantage in rigid wiring.

Which termination suits which conductor?

Solid wire plugs straight into screw, spring and push-in terminals because it is dimensionally stable. Fine-stranded wire, by contrast, needs a ferrule in many terminals so the individual wires do not splay, no strands are lost and the contact pressure is spread evenly.

Ferrules are crimped gas-tight onto the stripped strand with a crimping tool. For push-in terminals, ferrules with a plastic collar are common because they guide insertion and insulate. Fine-stranded wire must not go under a plain screw terminal without a ferrule, since the screw crushes individual wires and the contact works loose.

Are there differences in current and handling?

At the same copper cross-section the current capacity of stranded and solid wire is virtually identical, because it depends on the cross-section, not on the number of individual wires. The skin effect only matters at high frequencies and is negligible at mains and control voltages.

• Soldering: solid wire tins easily, stranded should be twisted and lightly pre-tinned before soldering.
• Stripping: with stranded wire use sharp blades so no individual strands are cut off.
• Board work: for header pins on PCBs solid wire is often preferred, stranded for moving leads.
• Cost: solid wire is cheaper, highly flexible strand is dearer due to the elaborate stranding.

Frequently asked questions