McIntire joint
An electrical connection spliced together by means of a sleeve (double tube of copper for this purpose).
McIntire joint: a copper-sleeved wire splice for low-voltage circuits
A McIntire joint is a mechanical splice made by inserting the stripped ends of two conductors into opposite ends of a short copper tube (the sleeve), then compressing the sleeve radially around both wires to form a permanent connection. The tube is typically soft copper, roughly 0.5 to 1 inch long depending on wire gauge, with an internal diameter just large enough to accommodate the conductor ends side by side or end to end. Once compressed with a special tool or vise, the deformed copper grips the wires through friction and surface contact.
This joint was common in electrical wiring practice throughout the late 19th and early 20th centuries, particularly in low-voltage telegraph, telephone, and early power distribution systems. The name appears in older electrical manuals and engineering references but is now rarely encountered in new installations. Modern practitioners are more likely to encounter existing McIntire joints during renovation of old buildings or heritage electrical systems.
How it performs and fails
The joint's strength depends entirely on the quality of the compression and the condition of the copper sleeve. A properly made joint can carry current with minimal resistance and modest mechanical strength, adequate for many historical applications. Deterioration occurs when the copper oxidizes at the contact surfaces, increasing resistance and generating heat during current flow. Vibration and thermal cycling can also cause the sleeve to loosen, degrading the connection further. The lack of corrosion protection (unlike modern shrink-tubed or soldered joints) makes these splices vulnerable in damp environments.
The McIntire joint belongs to a family of mechanical splices that preceded soldering and crimping as dominant methods. It required no solder, flux, or heat source, making it practical for field work in an era before portable soldering equipment was standard. However, it demanded both a proper tool and operator skill, and offered no visible indication of connection quality. Modern electrical codes generally do not permit McIntire joints in new work; they are encountered only as existing installations subject to maintenance or replacement.