The ideal
joint achieves a balanced match with the electrical, chemical, thermal, and
mechanical characteristics of its associated cable. In actual practice, it is
not always economically feasible to obtain a perfect match. A close match is certainly
one of the objectives.
The splicing
or joining of two pieces of cable together can best be visualized as two
terminations connected together. The most important deviation, from a theoretical
view, between joints and terminations is that joints are more nearly extensions
of the cable.
The splice
simply replaces all of the various components that were made in to a cable at
the factory with field components. Both cable ends are prepared in the same
manner unless it is a transition joint between say PILC and extruded cables.
Instead of
two lugs being attached at the center of the splice, a connector is used. At
each end of the splice where the cable shielding component has been stopped,
electrical stress relief is required just as it was when terminating.
Connector:
Joins the two conductors together and must be mechanically strong and
electrically equal to the cable conductor. In this application, the ends of the
connector are tapered. This provides two functions:
1) It provides a sloping surface so that the
tape can be properly applied and no voids are created
2) Sharp
edges at the end of the connector are not present to cause electrical stress points.
Penciling:
On each cable being joined, you will notice that the cable insulation is
“penciled back. This provides a smooth incline for the tape to be applied evenly
and without voids.
Insulation:
In this application, rubber tape is used. Tape is applied to form the stress
relief cone at each end of the splice. The overlapped tape continues across the
connector to the other side. The thickness at the center of the splice is dictated
by the voltage rating.
Conducting
Layer: Covering the insulation is a layer of conducting rubber tape that is
connected to the insulation shield of the cable at both ends of the splice.
Metallic
Shield: A flexible braid is applied over the conducting rubber tape and connects
to the factory metallic portion of the cable on each end. This provides a ground
path for any leakage current that may develop in the conducting tape.
There must
be a metallic neutral conductor across the splice. This may be in the form of lead,
copper concentric strands, copper tapes, or similar materials. It provides the fault
current function of the cable’s metallic neutral system.
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