A modern autosplice is a simple device made up of several components: a cylindrical shell tapered at both ends, two sets of tapered jaws, two springs, a spring divider, two cups, and two conductor guides. An exploded view of a standard autosplice design is shown in Figure 1.
The splice is installed by pushing the free conductor ends into the openings on either end of the splice body. Installation of a standard autosplice is illustrated in Figure 2. When inserted into the splice, each conductor end goes into a small metal cup that is just larger than the conductor outer diameter. The cup helps to prevent "ballooning" and spreading of the conductor strands during the installation. When the conductor is pushed against the end of the jaws, the jaws move back into the splice body against the compression spring which allows them to open to admit the conductor. The installation is complete when each conductor end is pushed completely through the jaws, and both cups are clear of the jaws. When conductor line tension is applied, the jaws are pulled toward the narrow end of the splice body, which causes them to grip the conductor. High conductor tension provides a high normal force between the splice body, jaws, and conductor, which results in good electrical and mechanical contact.
Autosplices have been submitted to the authors from B.C. Hydro for failure evaluation. The two most common symptoms of failure were simple overheating of the splice, or complete separation of the splice from the conductor. Many of the failures could be attributed to the installer having not pushed the conductor far enough into the autosplice.
To ensure complete insertion of the conductor, the installer is required to mark the conductor at the recommended insertion depth of half the splice length. This is not easily done on live conductors and under poor weather conditions, and often the insertion depth is estimated without marking. The autosplice gives the installer no feedback on the position of the conductor, and the jaws may initially hold the conductor even if it is inserted only part way. If the installer has difficulty in pushing the conductor against the closing force provided by the spring, it may be interpreted as a complete installation even though the conductor may be only part way through the jaws. If the conductor is pulled all or part of the way out of the splice after it has started to enter the jaws the cup usually comes off in the jaws, which increases the chance of a misinstallation if the conductor is reinserted. For a misinstalled autosplice, complete separation of the splice from the conductor often occurs, which results in a live line falling to the ground. It is difficult to predict how long an improperly installed splice may hold before it fails, and it may be in service for months or even years before a failure occurs.
The authors, working on a project supported by B.C. Hydro, conceived of and patented a design that will prevent the splice from being incorrectly installed. The design has the following features:
The installation procedure for the improved splice is illustrated in Figure 4. The conductor is inserted through the guide and directly into the jaws, which are held open by the plug. Since there is very little resistance on the conductor when it is pushed through the open jaws, ballooning of the conductor strands is not a problem and the cup is not required. The advantage of not having the cup is that at this point in the installation the installer can still pull the conductor out of the splice and reinsert it without damaging the splice. When the conductor reaches the plug, resistance is encountered, and increased force is required to dislodge the plug. When the plug is pushed out, the jaws are released and they snap around the conductor due to the force of the spring. A positive indication of complete installation is given by an audible "click" and sudden forward movement of the conductor as the jaws are released.
The modified autosplice design solves the installation problems associated with the old design, but still requires full tension lines for proper operation. Once installed, the modified splice operates exactly the same as the old design. The modified design has only been proof-of-concept tested to date, and is not yet in general production. Power-tech Labs is presently seeking a manufacturer to produce the improved autosplice design.
C.P. Morton and V.L. Bucholz are with Powertech Labs Inc., in Surrey, B.C.