equipment (e.g. racks, experimenter ORUs etc). When the electrical properties of the user equipment are known, the individual MO containing the SSPC can be selected. The MOs are conceived as plug-in units (in-orbit replaceable) and will be available in different ratings (limitation current adjustable) such that user demands can exactly be matched. Such a design provides outstanding features with respect to maintainability and accommodation of different user. The DB can be applied as a common building block throughout the distribution systems of all COLUMBUS elements. It shall be mentioned finally that in spite of the increased ‘on-resistance' of the SSPCs, the overall voltage drop of the power distribution assembly shall be kept to a minimum. Because the power quality at the user interface is strongly influenced by this overall voltage drop, it represents an important ‘figure of merit' of the distribution assembly. The present goal is to keep an overall value of approximately 2% which shall be achieved in the following way: • distribution systems of COLUMBUS elements shall comprise not more than two distribution levels; • SSPCs to be designed such that the individual device meets a voltage drop requirement of 0.75 V; • cable cross sections to be selected such that overall harness voltage drop stays within a limit of 1.5 V. Technical constraints and guidelines derived so far have been synthesized into a basic distribution design shown in Fig. 7.
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