745 قنوات قضبان التوزيع

745 BUS BAR TRUNKING

745-1 Bus bar trunking may be employed as horizontal feeders from main switch board to sub main switch
boards and as risers to the different floor distribution boards. The bus bars shall be totally enclosed in m etallic
housing of substantial construction and of adequate strength to withstand the electro- mechanical forces that may
be induced by the prospective short circuit current.

745-2 All bus bar trunking shall be so designed and arranged that they are free to expand and contract without
detriment to themselves or to adjacent parts of the installation. All dead ends of bus bar trunking shall be closed.
Fire barriers shall be provided at each floor level.

745-3 All bus bar trunking shall be surface mounted and so installed that they are inaccessible to unauthorized
persons. They shall be securely supported and only unbroken lengths shall be permitted at floor crossings. Bus
bar trunking shall not be installed in lift shafts.

745-4 No branch connections shall be permitted except through tap off units. Tap off units shall incorporate the
required excess current protective devices.

NOTE- Clause 507 allows omission of excess current protection if floor distribution board is in the same room.

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745-5 All bus bars employed in bus bar trunking shall be of high conductivity copper supported on adequately
rated and sized insulators.