ABB REL 551 2.3 Series Installation And Comissioning Manual page 38

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Installing the communication cables
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Note also that recommendation about cable lengths given for modules according ITU/
EIA interface, not short range galvanic module, are under the assumption that the two
equipment, protection terminal and communication, are within the same building and
that the earthing system of the building is well carried out. It also presumes that the en-
vironment is relatively free from electromagnetic noise.
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