Should I use solid or stranded (flexible) cable?
In vehicles, construction machines and all vibrating installations, stranded flexible conductor is used. Solid conductor fatigues and breaks under repeated bending and vibration; the break usually stays invisible under the insulation and shows up first as a voltage drop and then as a complete break. The cross-section calculation is the same for both types; what changes is mechanical endurance and the connection method.
Electrically there is no meaningful difference between the two types: copper of the same cross-section shows the same resistance, and the calculation ΔU = 2 x L x I x 0.0175 / A is the same for both. The difference is entirely mechanical.
Stranded (flexible) conductor is woven from fine wires; because each wire bends to a small radius, its fatigue endurance under vibration and repeated motion is high. This is the right choice for vehicle-mounted runs, moving arms, lid crossings and control cables.
Solid conductor is economical in fixed installations and grips a terminal block easily, but under vibration it fatigues and breaks at a single cross-section.
Points to watch when using stranded cable:
- The end must always be terminated with a suitable ferrule or crimp lug; if the bare braid is clamped into a terminal block, the wires spread and the contact surface and clamping force are lost over time.
- Do not fill the end with solder and clamp it into a terminal block; solder creeps, the connection loosens and heats up.
- Crimping is done with a lug of the correct size and the correct die; squashing it by eye with pliers leads to high resistance.
Diagnostic clue: if the device cuts out when shaken and recovers when it stops, first measure the voltage drop under load; a drop above 0.5 V points to a broken wire or a poor termination.
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