splice

A splice is a permanent joint where two conductors are joined end-to-end, then insulated. Unlike a connector or terminal that allows disconnection, a splice is meant to stay put. It carries the same current as the wire itself and must maintain continuity of both electrical conductivity and mechanical strength. Splices appear in power distribution, control circuits, and signal lines wherever wire runs must be extended or repaired without adding bulk or introducing a discontinuity.

The basic method is to strip insulation from both wire ends, overlap or twist the bare conductors together, then crimp or solder them. Soldered splices use soft solder (typically 60/40 tin-lead or lead-free alloys) and require a hot iron and flux; the joint cools to solid mechanical connection. Crimped splices use a metal sleeve, usually copper or aluminum, pushed over the overlap and crushed with a dedicated tool. Some trades favor twisting, soldering, and taping as a budget method, though it produces a larger, weaker joint than crimping. The choice depends on wire gauge, current rating, environment, and labor cost.

Insulation is critical. Once the conductor joint is made, it must be covered with electrical tape, heat-shrink tubing, or a splice cap to restore the dielectric rating of the original cable. Bare joints will corrode, collect moisture, and risk shock or short circuits. Heat-shrink tubing is favored in damp or harsh environments because it bonds to itself as it cools, sealing against moisture and physical damage. Tape is cheaper and faster but prone to peeling and creeping over time.

Resistance is the enemy. A poor solder joint or loose crimp creates a high-resistance contact that heats under load. This causes insulation to soften, connection to degrade further, and eventually arcing or fire. Loose twists that rely only on tape degrade fastest. Crimps that use the wrong tool size or wrong sleeve material also produce intermittent high-resistance joints. In high-current circuits, even a small resistance rise is dangerous; in control or signal circuits, resistance causes voltage drop that affects downstream equipment.

Building codes and standards limit where splices are allowed. In permanent building wiring, splices must be made inside accessible junction boxes or enclosures. Direct burial or inside-wall splices are prohibited because repair or inspection becomes impossible. Industrial practice is stricter still: many critical systems require all splices to be counted, marked, and traceable. Telecommunications and aviation splice only with rated connectors or factory-terminated assemblies to avoid field-generated weak points.