La valeur de la création d’un cadre d’interprètes spécialisés

When long lengths of conductor are required, it may be necessary to splice or join two pieces end to end. Splicing should serve two purposes: to maintain electrical conductivity and to maintain the physical strength of the conductor through the splice.

Where the conductor is small and relatively inexpensive, it may be advisable to avoid splices altogether.

In the case of a distribution line, this would be done by simply deadending the conductor to the pole nearest its end and cutting off the remainder, except for a short tail. The next length of conductor used to continue the line would also be deadended at that pole. A connector (p. 105) would then be used to join together the two loose tails, providing the electrical continuity.

For copper and steel conductor, splices can be made by properly twisting the conductors together and soldering. But special hardware is typically used for this purpose. Four basic types of acceptable splices are described below. Parallel clamps should not be used to splice two conductor together under tension because this can damage the conductor.

However, parallel connectors can be used when the

Fig. 71. Insulated copper line secured to a distribution pole by wrapping once. Stapling the conduc-tor prevents movement down the pole.

Fig. 69. A locally-fabricated J-hook with a flexible insert to support insulated ABC in Nepal.

Fig. 70. Several rudimentary approaches for fixing an insulated conductor to a pole.

(a) (b)

staples

pole

conductors are not under tension, such as between the loose ends of two deadended conductors on the same pole.

Wrapped/twisted splices.

This splice is used on small solid conductors made of copper or steel.

The two wires are laid parallel and one conductor is wrapped over the other in reverse turns. Such a splice is shown in Fig. 72. To improve the conductivity and strength the splice

is soldered. This type of splice requires discipline and an appreciation for quality workmanship if it is to be used successfully.

Twisted splices should not be used with ACSR, AAAC, and other aluminum multiple-wire conductor because these do not provide any mechanical strength and would introduce line loss due to poor conductivity across the splice.

Compression splice

This type of splice is very reliable and now commonplace. For small size conductors, the cost of this splice is very attractive. A compressible splice is a metal tube that slides over the ends of the conductors to be spliced and is squeezed or crimped onto the conductor by a compression tool. The compression sleeve should only be used for the size of conductor for which it has been specified. Furthermore, the compression tool must be fitted with the dies for that particular sleeve. If properly installed, the sleeve should be able to support the full tension of the conductor. A disadvantage of this splice is that is cannot or should not be made without the proper compression tool and die.

For multi-layered ACSR transmission conductors, a couple of sleeves are installed over each other. The inner steel sleeve is used to secure the two ends of the steel core and the outer sleeve is used over the outer aluminum strands and the inner sleeve. However, for the ACSR commonly used for distribution line, this type of splice is increasingly being replaced by a single sleeve placed over the entire conductor.

Sizes range from solid #8 AWG (8 mm²) copper conductor and #4 AWG (21 mm²) ACSR on up.

For small solid-core conductors, a compression splice would be the best recommendation. This splice will offer both good mechanical strength and optimum electrical conductive properties. Hand operated mechanical presses are reasonably priced and can provide years of service if cleaned and maintained periodically.

Preformed splice

This splice is made up of preformed tempered wire that is installed by hand over the conductor as in the case of preformed deadends. The splice principal is based on the “Chinese finger puzzle”. As tension is applied to the splice the covered preformed wires will grip the spliced conductor firmer. As in the case of preformed deadends, preformed splices should not be reused. These types of splices do not require special tools like the press for the compression splices. Splices for small sizes are not readily available below #6 AWG and the splices may not accept full tension.

Fig. 72. A twisted splice before soldering.

Automatic splice

This splice is based on griping wedges inside of a tapered tube (Fig. 73). The bared end of each conductor to be spliced is inserted into the tube with the gripping jaws. When the ends are fully inserted and then placed under tension, the gripping wedges are pulled toward

each end, further tightening their grip on the conductor. The advantage of this splice is that its application requires no special tools. It is the easiest and most trouble-free method of splicing conductor. On the other hand, this type of splice is usually the most expensive of all the mechanical splices available, although prices have been going down as they have gained in popularity. These splices cannot be reused.

Automatics splices are commonly available for solid copper conductor down to AWG #8 (8 mm²) and for ACSR down to AWG #4 (21 mm²).

Knotting

An unconventional but fairly common practice for some low-cost schemes that use smaller insulated conductor is to join the conductors by knotting together their ends. In this manner, it is the knot that provides the strength in tension. The insulation on the free ends of the knot is partially removed and the ends should then be connected using one of the techniques described earlier (p. 105). This is not a conventionally accepted splice and it is not clear how durable it is, what type of knot least compromises on the strength of the line, etc.

Fig. 73. An exploded view of an automatic splice. (Source:

Fargo Mfg. Co., Poughkeepsie, NY.)

X. Guys and anchors

When a line deadends on a pole or when there is a deviation in the direction of the conductor at a pole, it places a permanent force on the pole. If significant, this force must be counteracted by a guy wire that transfers the force to an anchor in the ground. Guy wires are usually made of stranded steel that is heavily galvanized. However, where guys are near chemical plants or in mining districts, galvanized wire will not stand up, and copper-clad cable may be used under such conditions.

While guy wires are commonly used with conventional medium- and low-voltage lines, mini-grids may use considerably smaller conductor. When this is the case, these smaller conductors can be placed under less tension, and forces which are in turn transferred to the poles at bends or at dead ends are

correspondingly smaller and may not require guys to counteract. Furthermore, if ground clearance is more than adequate, lines can have considerable sag, further reducing the tension (see sag-tension relationship, p. 81).

In some countries, guy wire can be useful and tends to “disappear”, placing the system at risk. Therefore, if a guy is essential to ensure the proper operation of the system, all member of the community must be aware of this to avoid tampering or theft. The guy must also be protected vehicles and pedestrians from accidentally running across it.