Strain Relief and Routing: Wires Fail Where They Are Held

Clamp the outer sheath or the insulation, and leave enough slack inside that the conductors themselves are never in tension. That is what the back grip of a crimp terminal does, what a cable gland does, and what the moulded boot on a purchased lead does. If a cable is pulled hard, the clamp should take the load and the joints should not even notice. Inside an enclosure, leave a SERVICE LOOP — a little extra length so the board can be lifted out without unplugging everything. It costs a few centimetres of wire and saves the joint that would otherwise be torn out by the first person to open the box, who is usually you.

A wire bent around a tight radius concentrates all the strain into a short section of copper. Bent repeatedly there, it work-hardens and cracks. Give it room. The usual guideline is a bend radius of several times the cable's own diameter — more for a cable that flexes constantly. Where a wire must move repeatedly, give it a generous loop rather than a tight corner, so the bending is spread out. Heat shrink extending past the joint helps here: it supports the wire for a centimetre or two on each side, so the flexing happens gradually along that length instead of abruptly at the joint's edge.

A wire passing through a hole in sheet metal will eventually be cut by it. The edge is sharp, the wire vibrates, and the insulation wears through — then the conductor shorts to the chassis. Fit a rubber grommet, or at minimum file the hole edge smooth and wrap the wire where it passes. This is not a refinement; it is the single most common cause of a mysterious intermittent short in anything that vibrates. Route away from heat and moving parts as well. A wire lying against something hot loses its insulation slowly and invisibly, and a wire near a hinge or a fan will find its way into it eventually.

Bundle wires that run together, but do not pull the ties tight enough to deform the insulation. A cable tie crushed down hard is itself a stress point, and over time it cuts in. Label both ends of anything that is not obvious from its colour. A wrap of tape with a number, or a printed sleeve, turns an hour of beeping out wires with a meter into a glance. Route deliberately rather than by the shortest path: along structure, away from heat, with the signal wires separated from anything carrying switched power. A harness laid out on purpose can be followed by someone who has never seen it, which is the actual test of whether it was done well.