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Clean Earth System

Oz over 4 years ago

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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0 Harry Macdonald over 4 years ago

A Nuclear Power Station has something similar, though, if I remember correctly the clean earth was connected to the dirty earth at one point (under the control, room?). The point, I was told, is that all the twisted pair cable screens and armours needed to be connected to earth once and once only.

Every multipair screened cable was glanded with an insulated gland and the glands connected so as to provide this path, so if there were two multipair cables from a junction box to the control room, one had its armour and screen used as the earth connection for all the minor cables and one did not. Keeping all this under control on a project with 50,000 cables was fun.

In a big Power Station there is a concern that the local earth and the earth bar earth may be very different , especially at the instant of a fault on the nearby 400kV system but someone cleverer than I had done the calculation of the chance of such a fault coinciding with someone touching the clean earth and deemed it sufficiently low.
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0 Harry Macdonald over 4 years ago

A Nuclear Power Station has something similar, though, if I remember correctly the clean earth was connected to the dirty earth at one point (under the control, room?). The point, I was told, is that all the twisted pair cable screens and armours needed to be connected to earth once and once only.

Every multipair screened cable was glanded with an insulated gland and the glands connected so as to provide this path, so if there were two multipair cables from a junction box to the control room, one had its armour and screen used as the earth connection for all the minor cables and one did not. Keeping all this under control on a project with 50,000 cables was fun.

In a big Power Station there is a concern that the local earth and the earth bar earth may be very different , especially at the instant of a fault on the nearby 400kV system but someone cleverer than I had done the calculation of the chance of such a fault coinciding with someone touching the clean earth and deemed it sufficiently low.
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Clean Earth System

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