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Clean Earth System

Oz
Hi everyone,

I received earthing system design for  the high rise building. Earthing system  single line diagram shows main earthing system and  separate earthing network as clean earth . In every IDF rooms (Telecom Room) there are earth bar and earth bars connected each other for every floors every IDF rooms and its connected in the end to the  main clean earth bar in the main telecom room and main clean earth bar connected to the separate earth pits with earth electrodes. There are main earthing system as well but there is no connection between the main earthing system and clean earth. Earth pits ,earth electrodes,earth bars are all separate .The thing is telecommunication rack fed by the industrial socket inside the IDF Room  and this sockets fed by UDB(UPS DB) in electrical room. UDB connected to the main earthing system within the earth bar inside the electrical room .Telecommunication rack cabinet body connected to the clean earth bar inside the IDF room. So after all separations between main earth and clean earth , they are connected through rack cabinet bonding. My question is what is the purpose  of the "clean earth " provided in this design . And what I tried to explain above is correct practice?
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    alanblaby:

    Yes, I'd like to know the theory too.

    We installed a large DB in a hospital suite to supply a single scanner, and its associated auxilaries.

    The DB/Panel was custom made by T. Clarke. It was fed direct from the substation by a 5 core SWA cable, iirc, 185mm, though it may have been 95mm, its 2 years ago now.


    Inside the panel was the usual earth bar and outgoing circuit connections on it, then a separate 'Clean Earth Bar' which had a number of 10mm cables going to almost all machines in the room.

    Being as the earth was supplied direct from the substation to the DB, then how can that 'clean earth' be any different to the normal earth bar?


    Multiple connections (what used to sometimes be called "cross-bonds") reduce inductance. This is what's shown in Fig A444.2, Fig A444.3 and A444.4 in BS 7671 - and is also recommended by BS EN 50310.


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  • 0
    alanblaby:

    Yes, I'd like to know the theory too.

    We installed a large DB in a hospital suite to supply a single scanner, and its associated auxilaries.

    The DB/Panel was custom made by T. Clarke. It was fed direct from the substation by a 5 core SWA cable, iirc, 185mm, though it may have been 95mm, its 2 years ago now.


    Inside the panel was the usual earth bar and outgoing circuit connections on it, then a separate 'Clean Earth Bar' which had a number of 10mm cables going to almost all machines in the room.

    Being as the earth was supplied direct from the substation to the DB, then how can that 'clean earth' be any different to the normal earth bar?


    Multiple connections (what used to sometimes be called "cross-bonds") reduce inductance. This is what's shown in Fig A444.2, Fig A444.3 and A444.4 in BS 7671 - and is also recommended by BS EN 50310.


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