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EuroWire – September 2007
98
english
Advanced Mechanical
Protection Using
Polymeric Armour
By Paul Cinquemani, Bill Wolfe, Carroll Lindler, Paolo Veggetti and Marco Frigerio, Prysmian Power Cables & Systems USA
Abstract
Electric power and control cables can be
subjected to very high tension during
installation. As cables are pulled around
bends sidewall bearing pressure (SWBP)
should be monitored to keep it below
the limits set by industry standards
and manufacturer’s recommendations,
otherwise the cable can get damaged.
Typically,
manufacturers
and
cable
installers have used various ways to
protect cables from high sidewall bearing
pressures. Cable manufacturers use metal
clad armour of either aluminium inter-
locked armour (AIA) or continuously
corrugated metal armour.
Cable installers have several options.
They can increase the bending radius the
cable is pulled around or can design to
install shorter cable pulls and splicing the
several sections.
This paper will detail the development
and evaluation of a new design of power
cable that provides increased mechanical
protection without the use of metallic
armour while also improving overall
flexibility. The new design incorporates
a polymer layer that has been shown to
improve both the mechanical toughness
of electrical power cables while providing
improved flexibility compared to cables
using metallic armour.
The
data
presented
support
that
polymeric armour provides five times
better impact performance than metallic
armoured products. Power cables that
contain polymeric armour can achieve up
to 3,000 pounds/radius foot of SWBP.
This allows installers and customers to
install cables for longer distances without
the need for expensive splices which also
affects cable reliability.
1. Introduction
The NFPA National Electrical Code (NEC)
clearly defines the applications where
metal clad cables (Type MC) are required
to be installed or may optionally be used
in the occupancies covered therein
[1]
. The
specific types and requirements for such
metal clad cables are also clearly defined
in UL Standards 1569 and 1072
[2] [3] [4]
.
In many other locations and applications,
metal clad cable may be used as a
beneficial option, ie conduit replacement
or as an alternate design when greater
mechanical abuse resistant cable is desired
by the end user.
Figure 1
:
Conventional type MC – continuous corrugated aluminium sheath design
▲
Figure 2
:
Polymeric armour design
▲