CLAMP ASSEMBLY The present invention relates to a clamp assembly for supporting an elongate object and in particular, but not exclusively, to a clamp assembly for supporting an electrical cable in the nacelle of a wind turbine. Wind turbines use many different types of electrical cable for different applications, such as the transmission of signals and power to control different components of the turbine, e.g. to drive motors or pumps to adjust the pitch of the blades. Information from sensors, such as in the blades, is transmitted to the ground via cables for condition monitoring purposes. Lower voltage power is needed for lighting, whilst high voltage cables are used to bring power generated by the turbine located in the nacelle to the base of the tower for connection to switchgear and the grid. As the nacelle has to rotate with respect to the tower, also known as yaw, these cables must withstand twisting and/or pulling. By arranging the cables in the centre of the tower, tension in the cable is minimized and twisting becomes the most important issue. Typically, the cables are arranged along the circumference of some form of ring or frame and as the cables twist they tend to adopt a helical shape which will create a certain tension in the cables as the helical shape of the twisted cables needs some length compared to a straight cable. To overcome this problem, it is known to form a cable loop or drip loop at the bottom of the hanging cables which simply consists of an over length of cable hanging more or less loose to compensate for the twist of the bundle of cables. However, the cables are typically unsupported down the tower so the loading on the upper end region of each cable, particularly axially as a result of the cable’s unsupported weight, is significant which can overstress the cable insulation and cause the same to breakdown and fail due to partial voltage discharge effects. It is an aim of certain embodiments of the present invention to provide a clamp assembly for supporting an upper end region of an electrical cable in the nacelle of a wind turbine. It is an aim of certain embodiments of the present invention to provide a clamp assembly for retaining an upper end region of an electrical cable in a desired location within the nacelle of a wind turbine and supporting the weight of the remaining cable extending down the tower of the wind turbine, whilst accommodating/withstanding axial and torsional loading of the cable in use and protecting the same from such loads. According to a first aspect of the present invention there is provided a clamp assembly for supporting an electrical cable, comprising: an elongate lower clamp section for supporting a cable; a plurality of axially spaced apart upper clamp sections coupled to the lower clamp section; a plurality of adjustors each for selectively moving a respective one of the upper clamp sections towards or away from the lower clamp section; and at least one connecting member longitudinally coupling the upper clamp sections together. Optionally, each adjustor comprises a spring to resiliently accommodate lateral movement of the cable in use whilst ensuring a clamping force is consistently applied to the cable. Optionally, each clamp section comprises a curved region for engaging the cable. Optionally, the curved region of each clamp section supports a resilient liner for engaging and protecting the cable. Optionally, the lower clamp section and each upper clamp section comprise a pair of flanges extending in opposed directions from the respective curved region for coupling each upper clamp section to the lower clamp section. Optionally, the plurality of upper clamp sections each comprise a pair of laterally opposed upper clamp sections coupled together at corresponding first flanges thereof and to a corresponding flange of the lower clamp section at corresponding second flanges thereof. Optionally, each pair of laterally opposed upper clamp sections is coupled together at the first flanges thereof by a first adjustor of the plurality of adjustors, and each upper clamp section of each pair of laterally opposed upper clamp sections is coupled at the second flange thereof to the corresponding flange of the lower clamp section by a second adjustor and a third adjustor respectively. Optionally, an angle between the opposed flanges of each clamp section is around 120 degrees. Optionally, each flange comprises a hole and each adjustor comprises a bolt located through aligned pairs of the holes and engaged with a nut for providing said selective adjustment. Optionally, the spring of each adjustor is located between the nut and the corresponding flange of the respective clamp section. Optionally, the at least one connecting member is located between a head of each corresponding bolt and the corresponding flange of the respective clamp section and/or between the corresponding springs and the corresponding flange of the respective clamp section. Optionally, the spring of each adjustor is a compression spring. Optionally, the at least one connecting member is an elongate bar comprising an L- shaped cross section defining a wall region for protecting the spring. Optionally, the plurality of axially spaced apart upper clamp sections comprises at least three axially spaced apart pairs of opposed upper clamps sections, wherein each pair of opposed upper clamp sections is laterally coupled together at a respective first end region thereof by a first adjustor and at a respective second end region to the lower clamp section by a second adjustor and a third adjustor respectively, and wherein the first adjustors are longitudinally coupled together by a first elongate connecting member, the second adjustors are longitudinally coupled together by a second elongate connecting member, and the third adjustors are longitudinally coupled together by a third elongate connecting member. According to a second aspect of the present invention there is provided a nacelle for a wind turbine comprising a clamp assembly according to the first aspect of the present invention. According to a third aspect of the present invention there is provided a wind turbine comprising a nacelle according to the second aspect of the present invention. According to a fourth aspect of the present invention there is provided a method of supporting an electrical cable, comprising: locating a cable on an elongate lower clamp section; locating a plurality of axially spaced apart upper clamp sections over the cable; laterally coupling each upper clamp section to the lower clamp section; and longitudinally coupling each upper clamp section together with at least one elongate connecting member; and operating an adjustor to selectively move a respective one of the upper clamp sections towards or away from the lower clamp section. Optionally, each adjustor comprises a spring to resiliently accommodate lateral movement of the cable in use whilst ensuring a clamping force is consistently applied to the cable. Optionally, laterally coupling each upper clamp section to the lower clamp section comprises coupling at least three axially spaced apart pairs of opposed upper clamps sections to the lower clamp section to define at least three clamping regions along the cable Optionally, laterally coupling each upper clamp section to the lower clamp section further comprises laterally coupling each pair of opposed upper clamp sections together at a respective first end region thereof by a first adjustor and at a respective second end region to the lower clamp section by a second adjustor and a third adjustor respectively. Optionally, longitudinally coupling each upper clamp section together comprises longitudinally coupling the first adjustors together by a first elongate connecting member, longitudinally coupling the second adjustors together by a second elongate connecting member, and longitudinally coupling the third adjustors together by a third elongate connecting member. Optionally, operating each adjustor comprises rotating a nut of the adjustor to compress or decompress the spring which is mounted on a bolt of the adjustor engaged with the nut. Description of the Drawings Certain embodiments of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 illustrates an isometric upper view of a clamp assembly according to certain embodiments of the present invention; Figure 2 illustrates an isometric lower view of the clamp assembly of Figure 1; and Figure 3 illustrates an end view of the clamp assembly of Figures 1 and 2. Detailed Description As illustrated, a clamp assembly 100 according to certain embodiments of the present invention includes an elongate and axially oriented lower clamp section 102 and three pairs of axially spaced apart upper clamp sections 104,106,108 to surround a cable to be clamped in a desired position and orientation in the nacelle of a wind turbine. Alternatively, the clamp assembly may include single axially spaced apart upper clamp sections for cooperation with the elongate lower clamp section to clamp a cable therebetween. However, a plurality of axially spaced apart ‘three- section’ clamp arrangements desirably distribute the clamping load equally around the cable and also provides an amount of resilience in more than two directions, as described further below. The elongate lower clamp section 102 includes a central concave region 110 in cross section for partially accommodating and supporting a cable located thereon and a pair of longitudinal flanges 112,114 extending outwardly in opposed directions from the central region 110. Each flange 112,114 is angled downwardly from the horizontal by around 30 degrees. Each flange 112,114 includes three equally spaced apart holes along its length to provide opposed and laterally aligned holes. The inner support surface defined by the central region 110 of the lower clamp section 102 is substantially straight to ensure a cable supported thereon remains substantially straight. Alternatively, the inner support surface may be curved along its length, such as concave, to support a cable in a slight ‘hump-back’ orientation. Each of the upper clamp sections includes a central concave region 116 having the same radius of curvature as the lower clamp section to partially accommodate the cable, and a pair of flanges 118,120 extending in opposed directions from the central region 116. Each flange 118,120 includes a hole for receiving a bolt 122 engageable with a nut 124 to attach the corresponding pairs of upper clamp sections 104,106,108 to the lower clamp section 102. The upper flanges of each opposed pair of upper clamp sections are coupled together by a similar nut and bolt arrangement, such that the clamp assembly 100 effectively defines three clamp regions 150,160,170 wherein each clamp region includes three adjustors 155,165,175. Each curved region of the upper and lower clamp sections may include an optional liner 180 made of a resilient material, such as rubber, for protecting the outer material of the cable from the clamp sections. An angle between the opposed flanges of each of the upper and lower clamp sections is around 120 degrees. Each adjustor 155,165,175, e.g. each nut and bolt arrangement, of each clamp region 150,160,170 allows the respective pairs of opposed upper clamp sections to be selectively urged towards or away from each other and/or allows the respective pairs of opposed upper clamp sections to be selectively urged towards or away from the lower clamp section to thereby accommodate different diameters of cable and/or to increase or decrease a clamping force being applied on the cable. Each adjustor 155,165,175 includes a compression spring 126 located between the nut 124 and the flange of the corresponding clamp section. A washer may be located between the spring and the nut and/or between the bolt head and the corresponding flange. The nut of each adjustor may be configured to be vibration-resistant, such as being nylon-lined, e.g. Nyloc™ nuts, or the bolts may include one or more holes for receiving a split pin and the nuts may be castle nuts. As best shown in Figure 3, two of the three bolts of each clamp region 150,160,170 extend upwardly to diverge away from each other in view of space constraints within the nacelle, but alternatively they could extend downwardly to converge towards each other. Further alternatively, each bolt of each clamp region 150,160,170 may be oriented in substantially the same direction around the respective clamp region, i.e. in the clockwise or anticlockwise direction about a longitudinal central axis of the clamp assembly or cable. The three adjustors 155,165,175 of each clamp region are spaced apart by around 120 degrees about the longitudinal central axis of the clamp assembly to thereby desirably apply an evenly distributed clamping load to the cable in use. As illustrated in Figures 1 and 2, the axially aligned pairs of upper clamp sections 104,106,108 are coupled together by four longitudinally oriented connecting bars 130,132,134,136 each of which include equally spaced apart holes to align with the bolt holes in the flanges of the upper and lower clamp sections. In the illustrated embodiment, a connecting bar 130,132,134 is located between each corresponding spring 126 and the respective flanges of the upper clamp sections. A fourth one 136 of the connecting bars is located between the corresponding bolt heads of the upper adjustors and the respective flanges of the upper clamp sections. Alternatively, a connecting bar may be provided between each bolt head and the respective flanges and a further connecting bar may be provided between the springs of the upper adjustors and the respective upper clamp sections. Each connecting bar 130,132,134,136 aptly has an L-shaped cross section wherein a longer wall of the L-shaped profile serves to protect the corresponding springs from impact or the like and also adds bending stiffness along the length of the connecting bar. Alternatively, each connecting bar may be a substantially flat and elongate strip of material. Aptly, the connecting bars are a metals material such as stainless steel, but aluminium or a plastics material may be suitable for relatively lightweight applications. Aptly, the clamp sections are also a metals material such as stainless steel, but also may be aluminium or a plastics material for relatively lightweight applications. Desirably, the ‘three-part’ clamp regions 150,160,170 ensure an equal distribution of clamping pressure is applied to and around the cable, and the separate clamp regions of the clamp assembly allow the same to accommodate/withstand tolerance and shape changes of the cable along its length. The connecting bars provide the clamp assembly with a longitudinal stiffness to withstand bending and torsional loads applied to the cable in use, such as when the nacelle turns to the direction of the wind. Without the connecting bars, the upper clamp sections would deform and grip on the cable would be lost as a result of the torsional loading. The springs ensure a consistent clamping force is applied to the cable, whilst providing some resilience to each of the clamp regions in at least three directions to prevent damage to the cable, such as permanent deformation, e.g. compression set, or compromised integrity of the cable materials, due to the axial, compressive and/or torsional loads otherwise applied to the cable when the nacelle rotates with the wind and/or caused by the weight of the cable itself extending down the tower. Certain embodiments of the present invention therefore provide a clamp assembly for retaining an upper end region of an electrical cable in a desired position and orientation within the nacelle of a wind turbine, such as a cable/s connecting to the turbine itself or a communications cable/s, and for supporting the weight of the cable extending down the tower of the wind turbine. The clamp assembly is configured to accommodate and withstand axial and torsional loading subjected to the cable in use as a result of the nacelle rotating responsive to the direction of the wind and the weight of the cable itself. The cable assembly is configured to protect the cable from such loads and to prevent the integrity of the cable being compromised and ultimate failure of the cable which is time consuming and costly to repair/replace and could undesirably result in a short circuit event.