AU2001262519A1 - Aerial cable installation and aerial cable suspension device therefor - Google Patents

Description

Aerial Cable Installation and Aerial Cable Suspension Device therefor

This invention relates to aerial cable installations and aerial suspension

devices therefor.

It is known to provide aerial cable installations comprising an aerial

cable suspended from a plurality of spaced apart suspension points provided

on poles, towers and like upstanding supports. Typically the cable is

suspended from the suspension points through respective suspension devices

each of which comprises a clamp provided with a suspension eye and

comprising two saddle members engaging the cable on diametrically opposite

sides thereof and bolted together. One of the functions of the clamp is to

apply a clamping force to the cable which allows slippage of the cable through

the clamp when the cable is subjected to an unbalanced load in the cable spans

immediately adjacent the clamp to reduce this imbalance. The clamping

compression force and the coefficient of friction between the contacting

surfaces of the cable and clamp determine the frictional force opposing

slippage due to an unbalanced load in the cable spans immediately adjacent

the clamp and in a prior art clamp as shown in Figure 4 of the accompanying

drawings the clamping compression force is adjusted during installation by

using spacers of a selected thickness (for example 3.3 mm) between the saddle

members. In the illustrated prior art clamp 1, which is obtainable from

Dulmison of Corby, Northants, England, two saddle members 2 and 3 engage the cable 4 on diametrically opposite sides thereof and are bolted together by

respective nut and bolt fastener assemblies 5 which pass through aligned holes

in flanges 6 and 7 of the saddle members 2 and 3 with respective spacers 8, in

the form of washers, positioned between the flanges 6 and 7. The nut and bolt

assemblies 5 are tightened until the flanges 6 and 7 engage with the spacers 8.

As will be appreciated the spacers limit further movement of the saddle

members towards each other and for a given torque applied to the bolts which

bolt the saddle members and spacers together the clamping compression force

applied to the cable and thus the frictional force opposing slippage will

depend on the actual diameter of the' cable and the thickness of the spacers.

We have discovered that the above-described clamp, whilst suitable

for use with metallic cables having relatively close tolerance outer diameters

(for example ± 3%), is not particularly suitable for use with cables such as all-

dielectric self-supporting (ADSS) cables which have relatively large tolerance

outer .diameters (for example ± 5%) since the variation in the diameter of a

latter cable along its length results in a variation of the force opposing

slippage depending upon the actual cable diameter at the location of the clamp

along the length of the cable. This problem of diameter variation is

exacerbated because an ADSS cable is more compressible than a metallic

cable and also requires reinforcing rods to be wound about the cable at the

clamping location thereby introducing a further tolerance on the cable

diameter. An object of one aspect of the invention is to avoid dependence of the

clamping force and thus the force opposing slippage of the cable in the clamp

on the actual diameter of the cable at the location of the clamp.

The invention includes an aerial cable installation comprising an aerial cable suspended from a plurality of spaced apart suspension points, said cable

being suspended from at least one of said suspension points through a

suspension device comprising a clamp comprising two saddle members

engaging the cable on diametrically opposite sides thereof and an adjustable

biasing arrangement biasing the saddle members towards each other to clamp against the cable with a selected clamping force, said saddle members being

movable further towards each other but for the presence of the cable

therebetween.

Preferably the adjustable biasing arrangement comprises a plurality of

nut and bolt assemblies extending through aligned holes in respective flanges

of said saddle members, each assembly including a helical spring mounted on

the bolt thereof between said flanges and the nut or a bolt head of the

assembly, said springs being compressed a predetermined amount which is

adjustable by tightening or loosening said assemblies.

It will be understood that instead of nut and bolt assemblies extending

through aligned holes in the flanges of the saddle members the adjustable

biasing arrangement may comprise a plurality of threaded studs fastened to

one of the saddle members and extending through holes in a flange of the other saddle member. In this case, each stud has a helical spring mounted

thereon between said flange and a nut threaded on said stud, said springs

being compressed a predetermined amount which is adjustable by tightening

or loosening said nuts.

The invention also includes a method of compressing to a

predetermined length a helical spring in an installation as defined in the last

but one paragraph or that installation modified as described in the last

paragraph, said method comprising fitting a gauge comprising a tubular body

having a radially inwardly extending rim at one end thereof over the spring such that said radially inwardly extending rim of the gauge engages with the

end of the spring remote from the or a said flange or a washer beyond said end

of the spring in a direction away from said flange, and tightening said

assembly until the other end of the tubular body engages said flange.

It will be appreciated that the above method is applicable generally to

compressing to a predetermined length a helical spring mounted on a bolt or a

stud extending from a surface. In this case, the method comprises fitting a

gauge comprising a tubular body having a radially inwardly extending rim at

one end thereof over the spring such that said radially inwardly extending rim

engages with the end of spring remote from the surface, or a washer beyond

said end of the spring in a direction away from said surface, providing a nut

on said bolt or stud and tightening said nut and bolt or said nut on said stud

until the other end of tubular body engages said surface. The invention also includes an aerial suspension device comprising a

clamp comprising two saddle members for engaging a cable on diametrically

opposite sides thereof and a plurality of nut and bolt assemblies each

including a helical spring having a plurality of turns, said assemblies being

adapted to extend through aligned holes in respective flanges of said saddle

members such that said springs bias the saddle members together in use.

In order that the invention may be well understood an embodiment

thereof, which is given by way of example only, together with some

modifications will now be described with reference to the accompanying

drawings in which:

Figure 1 shows part of an aerial cable installation;

Figure 2 is a schematic cross-sectional view taken along the line π-LT

in Figure 1 and to a larger scale;

Figure 3 is a schematic cross-sectional view of a part m of Figure 2 to

a larger scale and showing compression of a spring to a predetermined length;

and

Figure 4 is a schematic cross-sectional view similar to that of Figure 2

but of a prior art clamp of known aerial cable installation.

Referring to Figure 1 there is shown an aerial cable installation

comprising an all-dielectric self-supporting (ADSS) cable 10 suspended from

a suspension point, schematically indicated by dotted line 12, provided on an

upstanding support such as a pole or tower (not shown). As will be understood, the aerial cable 10 is suspended from a plurality of suspension

points 12 spaced apart along the cable.

The cable is suspended at at least one and preferably all or most

suspension points through a suspension device 13 comprising a clamp 14 provided with a suspension eye 16 and comprising two saddle members 18, 20

engaging the cable on diametrically opposite sides thereof as better shown in

Figure 2. Am adjustable biasing arrangement biases the saddle members 18,

20 towards each other to clamp against the cable with a selected clamping

force. This clamping force between the clamp and the cable allows slippage

of the cable through the clamp when the cable is subjected to an unbalanced load in the cable spans immediately adjacent the clamp of more than a

predetermined amount. When the saddle members clamp against the cable 10

with the selected clamping force a gap 21 remains between the saddle

members which would allow the saddle members to move further towards

each other but for the presence of the cable 10 between the saddle members.

If a smaller diameter cable were clamped in the clamp with the same clamping

force the gap 21 between the saddle members would be smaller and if a larger

diameter cable were clamped in the clamp with the same clamping force the

gap 21 would be larger. Thus, the provision of the gap between the saddle

members enables the clamp to apply a selected clamping force to a cable such

as an ADSS cable having a large tolerance outer diameter. The adjustable biasing arrangement may comprise any suitable device

or plurality of elements arranged to resiliently bias the saddle members

towards each other, and in the disclosed embodiment, the adjustable biasing

arrangement comprises nut and bolt assemblies 22 extending through aligned

holes 26, 28 (Figure 3) in respective flanges 30, 32 of the saddle members 18,

20 and including respective helical springs 24. The helical spring 24 in each

assembly 22 has a plurality of turns and is mounted on the bolt between the

flange 30 of the saddle member 18 and the nut 34 of the assembly. The spring

is compressed a predetermined amount by tightening or loosening the

assembly.

In the illustrated embodiment four nut and bolt assemblies 22 are

provided although three assemblies only are visible in the figures. The

assemblies are provided in longitudinally spaced apart pairs, one pair to each

side of a central portion of the clamp from which a suspension linkage 36

extends (as shown in Figure 1) and each pair comprising a respective

assembly to each side of the cable 10 (as shown in Figure 2).

Although not preferred it is to be understood that the bolts in the

assemblies 22 could be inverted in which case the helical spring 24 would be

mounted on the bolt between the flange 30 and the bolt head 38 rather than

between the flanges 30 and the nut 34.

Although also not preferred the bolts in the assemblies of the

illustrated embodiments may be replaced with threaded studs fastened to the saddle member 20 and extending through through holes 26 in the flange 30 of the other saddle member. It will also be understood that the springs may be

replaced by resilient plastics tubes although again this is not preferred.

Referring back to Figure 1, mechanical reinforcing rods 40, for example of galvanised steel are helically wound about the cable 10 over a

length thereof which includes that region of the cable in which the saddle

members clamp against the cable. Further, armour rods 42, for example of an

aluminum alloy, are helically wound over a portion of the length of cable

provided with the reinforcing rods including that region which is to be

clamped. To fit the clamp 14 to the cable, the saddle members 18 and 20 are

positioned to engage the armour rods 42 of the cable on diametrically opposite

sides thereof. The armour rods 42 and reinforcing rods 40 are omitted from

Figure 2 for simplicity. The nut and bolt assemblies are fitted through through

holes 26 and 28 of flanges 30 and 32 and the assemblies are tightened to

compress the. springs 24 to bias the saddle members towards each other to

clamp against the cable. The assemblies 22 are tightened using a torque

wrench to provide a desired clamping force between the clamp 14 and the

cable. For example the tightening torque applied to nuts 34 of the assemblies

may be 50Nm to provide a clamping force which allows slippage of the cable

when an unbalanced load in the cable spans immediately adjacent the clamp

reaches 7kN to 15kN. After the clamp 14 has been fitted to the cable the suspension linkage

36 is attached to the clamp and the suspension eye 16 fitted to the suspension

point 12.

As an alternative to using a torque wrench to control tightening of the

assemblies 22 to provide a required clamping force, the present mvention

provides according to another aspect thereof a method of compressing the

helical springs 24 in the assemblies 22 to a predetermined length which

provides a required clamping force. With reference to Figure 3, this method

uses a gauge 50 comprising a tubular body 52 having a radially inwardly

extending rim 54 at one end thereof.' The gauge 50 is fitted over the spring 24 of an assembly such that the rim 54 engages with a washer 56 between the end

of the spring remote from the flange 30 and the nut 34. The nut 34 is then tightened, as indicated by arrow 57, until the other end 58 of the body 52

engages the flange 30. The gauge is then removed and used on another

assembly. In this way, each spring is compressed to a predetermined length,

and assuming that the springs 24 used in the assemblies have the same length

and spring characteristics, each spring will provide the same, or substantially

the same, clamping force.

It will be appreciated that given appropriate diametrical clearances the

rim 54 of the gauge could be arranged to engage with the end of the spring

remote from the flange 30 in which case the washer 56 would be omitted. It will also be understood that gauge 50 may be used for any

application in which a helical spring mounted on a bolt or a stud extending

from a surface is to be compressed to a predetermined length.

Claims (8)

CLA S:

1. An aerial cable installation comprising an aerial cable (10) suspended

from a plurality of spaced apart suspension points (12), said cable being

suspended from at least one of said suspension points through a suspension

device (13) comprising a clamp (14) comprising two saddle members (18, 20)

engaging the cable on diametrically opposite sides thereof and an adjustable

biasing arrangement (22) resiliently biasing the saddle members towards each

other to clamp against the cable with a selected clamping force, said saddle

members being movable further towards each other but for the presence of the cable therebetween.

2. An installation as claimed in claim 1, wherein said adjustable biasing

arrangement comprises a plurality of nut and bolt assemblies (22) extending through aligned holes (26, 28) in respective flanges (30, 32) of said saddle

members (18, 20), each assembly (22) including a helical spring (24) mounted

on the bolt thereof between said flanges (30, 32) and the nut (34) or a bolt

head (38) of the assembly, said springs (24) being compressed a

predetermined amount which is adjustable by tightening or loosening said

assemblies.

3. An installation as claimed in claim 1, wherein said adjustable biasing

arrangement comprises a plurality of threaded studs fastened to one of said saddle members and extending through holes in a flange of the other saddle

member, each stud having a helical spring mounted thereon between said flange and a nut threaded on said stud, said springs being compressed a

predetermined amount which is adjustable by tightening or loosening said

nuts.

4. An installation as claimed in claim 1, 2 or 3 wherein said cable is an

all-dielectric self-supporting cable (10).

5. An installation as claimed in' any one of the preceding claims, wherein

said cable is provided with mechanical reinforcement (42) in the region in

which said saddle members clamp against the cable.

6. A method of compressing to a predetermined length, a helical spring

(24) in an installation as claimed in any one of claims 2 to 5, said method

comprising fitting a gauge (50) comprising a tubular body (52) having a

radially inwardly extending rim (54) at one end thereof over the spring (24)

such that said radially inwardly extending rim of the gauge engages with the

end of the spring remote from the or a said flange (30, 32) or a washer (56)

beyond said end of the spring in a direction away from said flange, and

tightening said assembly until the other end of the tubular body engages said

flange.

7. A method of compressing to a predetermined length a helical spring

mounted on a bolt or a stud extending from a surface, said method comprising

fitting a gauge comprising a tubular body having a radially inwardly extending

rim at one end thereof over the spring such that said radially inwardly

extending rim engages with the end of spring remote from the surface, or a

washer beyond said end of the spring in a direction away from said surface,

providing a nut on said bolt or stud and tightening said nut and bolt or said nut

on said stud until the other end of tubular body engages said surface.

8. An aerial suspension .device comprising a clamp comprising two

saddle members (18, 20) for engaging a cable (10) on diametrically opposite

sides thereof and a plurality of nut and bolt assemblies (22) each including a

helical spring (24) having a plurality of turns, said assemblies being adapted

to extend through aligned holes (26, 28) in respective flanges (30, 32) of said

saddle members such that said springs bias the saddle members together in

use.