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Street Lighting cable installation

sinu123
Hi All, 


This is regarding Street lighting cable installation which follows the BS standard 7671, In one of my project contractor has installed16Sqmm cable from first lighting column to the last lighting column. However, due to the impedance/earth fault, the cable size needs to increase from 16sqmm to 25sqmm (feeder pillar to the last lighting column) to get a compliant electrical calculation.

To avoid significant work in the ground, the contractor would like to install bigger size cable(25sqmm) from feeder pillar to the first lighting column and retain the small size (16sqmm) cable from first lighting column to the last lighting column in the ground.  

 Based on BS7671, could anyone let me know that using the bigger size cable from the FP to the first column and drop in cable size from the first column to the last column is acceptable?


Reagrds

Sinu123


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  • 0
    If it helps there is an example in BS 7671 of a circuit with two different cable sizes - appendix 15  Fig 15B - where 2.5mm² spurs are shown from a 4mm² circuit.


    If you really want something to quote - there are bits like 433.3.1 (i) which says that an overload protective device may be omitted where there's a reduction in the value of the current carrying capacity where the upstream protective device already provides overload protection and similarly 434.2.2 for fault protection but those don't really relate to Zs or v.d. requirements.


       - Andy.
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  • 0
    If it helps there is an example in BS 7671 of a circuit with two different cable sizes - appendix 15  Fig 15B - where 2.5mm² spurs are shown from a 4mm² circuit.


    If you really want something to quote - there are bits like 433.3.1 (i) which says that an overload protective device may be omitted where there's a reduction in the value of the current carrying capacity where the upstream protective device already provides overload protection and similarly 434.2.2 for fault protection but those don't really relate to Zs or v.d. requirements.


       - Andy.
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