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Corrugated Plastic Conduit Ducts
G. ABERG, TELEFONAKTIEBOLAGET LM ERICSSON, STOCKHOLM
UDC 621.315.616
621.315.671
LMF 823
The corrugation of plastic ducts increases their radial rigidity. The L M
Ericsson Network Department has developed a corrugating machine which
produces from thin-walled plain ducts a corrugated duct with the same (or
better) mechanical properties as a non-corrugated duct with walls 3^f times
as thick.
Non-corrugated plastic ducts are being increasingly used in outdoor conduits.
They have many advantages: low weight, which reduces the freight and
handling costs, no risk of corrosion of lead-sheathed cables, waterproof
conduit, a certain flexibility, reduced friction, which allows longer distances
between manholes, etc. These ducts, however, must have a fairly thick wall,
which makes their price high. Corrugation permits the use of thinner-walled
ducts and so reduces the price.
Non-Corrugated Plastic Ducts
Ordinary non-corrugated plastic tubing, 6 m in length, is a general commercial
commodity in most industrial and certain developing countries. The
diameter of the tubing varies. There are two reasons for this.
• Different diameters of duct are required in different parts of a local cable
network. Near the exchange large-diameter ducts are required to accommodate
multipair cables. This tendency will be accentuated through the
use of light cables and, to a still greater extent, if copper conductors are
replaced by aluminium. On the outskirts of the network and for secondary
cable runs, on the other hand, a smaller duct diameter is sufficient.
• The second reason is that, with different diameters of duct, the ducts can
be telescoped into one another and so form a more convenient transport
package. This is an important advantage when the ducts have to be transported
a long distance from the place of manufacture to the site of corrugation
and installation. The freight cost for ducts of a single dimension is
unreasonably high.
A set of ducts NTB 30101 contains nine ducts telescoped into one another.
Their outside diameter varies between 70 and 110 mm in intervals
of 5 mm.
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