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BS7671 Grouping Factors

Mark Freeman

Hi,

With reference to BS7671, in table 4C1 (Page 396) it states that:  Where horizontal clearances between adjacent cables exceed twice their overall diameter, no rating factor need be applied.

However when I reviewed table 4C4 (Page 398) it states that where the installation consist of a number of cables per ladder on a single tier, providing that they are spaced 1 cable diameter apart, no derating need be applied - as all tge 

Can anyone advise why one table states 2 OD spacing and the other states 1 OD spacing.

Many thanks!

M

  • 0
    Mark Freeman said:
    providing that they are spaced 1 cable diameter apart, no derating need be applied

    I don't see that in 4C4, it does give derating factors if spaced 1 cable diameter apart. 

  • 0

    it does give derating factors if spaced 1 cable diameter apart. 

    True, but for a single tier (number of trays or ladders is 1) the tabulated value is 1.0 for all numbers of cables. I'm not sure why it differs from 'item 4 of table 4C1' - unlike the earlier rows.

       - Andy.

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