The IET is carrying out some important updates between 17-30 April and all of our websites will be view only. For more information, read this Announcement

Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 5 replies
  • Subscribers 31 subscribers
  • Views 1935 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

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


Parents
  • 0
    As far as the regulations are concerned, the important thing is the total resistance of the cable to the end - however if this can be made compliant by increasing the cable size only at one end, or the other, or indeed for a short section in the middle if you need to, this is perfectly acceptable (note that joins do need to be accessible or sealed to be watertight,so a joint at a lamp post sounds sensible.).


    I presume from yuor description that the non-compliance is one of Zs at the far lamp versus the current required to trip the protective fuse or breaker, and a lower rated breaker is not a sensible suggestion?.

    Rather than the other problem, of voltage drop when the lights are all on - where a lower rated fuse or breaker will not help you, but the section of cable nearer the supply carries more current so is the more sensible to be reinforced anyway.

    The other possible solution is an RCD or RCBO for earth fault detection, but that is not ideal as arrangements have to be made for if it false trips in a thunderstorm or something, so perhaps OK for a restaurant car park, where there will be staff around, not for unattended operation.

Reply
  • 0
    As far as the regulations are concerned, the important thing is the total resistance of the cable to the end - however if this can be made compliant by increasing the cable size only at one end, or the other, or indeed for a short section in the middle if you need to, this is perfectly acceptable (note that joins do need to be accessible or sealed to be watertight,so a joint at a lamp post sounds sensible.).


    I presume from yuor description that the non-compliance is one of Zs at the far lamp versus the current required to trip the protective fuse or breaker, and a lower rated breaker is not a sensible suggestion?.

    Rather than the other problem, of voltage drop when the lights are all on - where a lower rated fuse or breaker will not help you, but the section of cable nearer the supply carries more current so is the more sensible to be reinforced anyway.

    The other possible solution is an RCD or RCBO for earth fault detection, but that is not ideal as arrangements have to be made for if it false trips in a thunderstorm or something, so perhaps OK for a restaurant car park, where there will be staff around, not for unattended operation.

Children
No Data

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines