The invention relates to a cabling method especially for installing thick electric cables for connection to electric devices, in which method the cables are brought to a cabling space, fitted and supported in place, cut and stripped at necessary locations, and the desired cables are equipped with connectors for installing to the electric device. The invention also relates to a cabling space used in this method.
Thick cables are typically installed in a fixed manner to an electric device to be connected. In Europe, cables are generally brought from below through a separate cable channel or chute to the device to be connected. In America, the cables are typically brought from above. Both in Europe and America, the cabling space is a fixed part of the electric device, i.e. this space is set as part of the device. Cabling is done physically from the front of the device.
Cabling usually comprises the following work stages: first the cables are brought to the cabling space, they are supported in place and their detensioning is arranged, which detensioning can also be done from outside the cabling space. Cables are often brought through cable bushings, in which case electrical safety regulations may apply (for instance in the U.S. and England cable-specific bushings and/or wall tubes are used). In double-insulated cables, the outermost sheath is opened and stripped as required. The outer-most ground and protective cabling is wound to a ground wire. In addition, the apparatus may have ground wires of its own or inside the cable. The phase conductors of the cable and possible internal ground conductors are arranged, cut and stripped open as required. Next, cable shoes are pressed with manual or hydraulic presses to the phase and ground conductors or other suitable connectors are connected to them in some other manner. Finally, the cable shoes or connectors are connected by screw fastening to the appropriate connectors of the electric device in the cabling space.
Connectors are used especially in smallish, easily bendable cables, whereby a light and small device can be connected to the cables using connector counterparts belonging to the device. Alternatively, the connector is part of the device, in which case the device can be installed only after the cables have been tightened. In thick cables, regulations, standards and various instructions as well as the physical size and bendability of the cables set restrictions to this connection method.
Installation methods using connectors have been developed, in which the back part of a cabinet or enclosure are used in cabling an electric device. A common feature in these constructions is that cabling in done before the electric device is connected to the back part of the cabinet or enclosure protecting the device or to a separate cabling field that is electrically connected to a counterpart of a connector belonging to the device. After cabling, the electric device is brought to the enclosure by means of rails, slides, conductors or some other controls and set exactly in place, whereby the counterpart of the connector in the cabinet or enclosure touches the connector in the device. Constructions of this type are found for instance in Toshiba frequency transformers and Merlin Ger switches.
Standards defining the minimum space exist for the cabling space. Frequency transformer standards include the Canadian standard C22.2, U.S. standard UL508C and international IEC 61800-5 (draft). In known solutions, it is often in practice necessary to increase the dimensions of the cabling space to be considerably bigger than the minimum requirements of the standards.
The known cabling described above has several drawbacks. The large bending radius and mass of thick cables as well as their termination require space. Because cabling is done from the front of the device, the cables should be grouped either parallel in the installation direction and/or stepwise in elevation utilizing the longitudinal direction. Especially in a small installation space, the cables must be bent outside the device for clamping the cable shoes, whereby the space required by the cables in the longitudinal direction increases significantly.
Because cabling is thus a fixed part of the device, the replacement or repair of the device requires that the cables be detached or a detachable terminal connector be used. Because a terminal connector must be detached from the front of the device, it increases significantly the size of the device. Detaching cables is often difficult or even impossible, since the clamping of the cable shoes stiffens the cables even further and deformations during use hamper significantly the moving of the cables.
There are hundreds of different thick cable types in the world. Because their size, the cabling practice and regulations, connection methods and the dimensioning rules of cables also vary greatly, it is practically impossible to use universal connectors with thick cables. In addition, the price of cabling in comparison with the actual device is often high, and an exact definition of the cables is possible in limited cases only.
The same drawbacks as described above apply to cabling installed to a cabinet or the back part of an enclosure, since cabling is brought from the connector of the electric device to a separate fixed cable connection space. An advantage of this type of construction is that as a whole the depth of the cabinet can be better utilized and the replacement or repair of the device is easier. In addition, the device need not be installed during cabling, whereby this space can be utilized in cabling. A disadvantage in comparison with the present invention is that due to electrical safety, the detaching of an active device must be secured by a disconnector. This means that a device-specific switch or locking device is required that is coupled to the disconnector or switch by a separate mechanism. In addition, fixed cabling causes the same problems as described above.