EXACTNESS
IN CABLE HANDLING, TERMINATING AND SPLICING
In a sense the only cable component necessary for transmitting
power is the conductor. Additional components are added
only when additional functions are required and justified.
These usually fall into the following areas:
(1)
Space is at a Premium. The simple substitution of
suspended insulated cables for bare overhead wires
at least triples the cost of a power circuit, and
the installation of a conduit or duct runs increases
the cost many more times.
(2)
Safety is of Prime Concern.
(3)
Once a decision to use insulated cables is justified
-- furnishing a design that will provide maximum performance.
(4)
An auxiliary component is required, such as a ground
monitoring wire.
It
is well established that, in most applications requiring
our immediate interest, space is at a premium. The basic
building blocks of a cable for this set of conditions
are: (1) a conductor; (2) an insulation; (3) a protective
sheath. Historically this construction has been reliable
through 600 volts and has a good record through 2000
volts. From 2001 to 5000 volts, a calculated risk is
involved. Above 5kV the cable, from a safety point of
view, should be treated like a bare conductor.
To
satisfy customers' safety requirements, or to improve
performance, one or more of the following is usually
added to the basic cable design:
(1)
Strand Shield
(2) Semiconducting Tapes
(3) Conductor Shields
(4) Grounding Conductors
(5) Insulated Control Wires
(6) Armor
Each
additional component added to the basic design requires
an additional degree of exactness in handling, terminating,
and splicing. Certain cable practices become mandatory,
otherwise what was intended in added safety and performance
can be completely defeated and become a potential hazard.
Following
are a few samples:
(1)
Shielded cables are vulnerable to mechanical damage
and must be handled with extreme care. (2) Shielding
systems must be grounded -- a floating shield is a
hazard.
(3) As a rule of thumb, any cable with a shield over
the conductor should be terminated with stress relief
cones.
(4) Semiconducting tapes must be removed at terminations
and the surface of the insulation cleaned.
(5) Grounding conductors must be continuous and grounded.
Sophisticated
cables cost more money. You get your moneys worth when
you take time to understand the function of each component
and make provisions for each component to work at top
efficiency
