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 21 replies
  • Subscribers 32 subscribers
  • Views 2958 views
  • Users 0 members are here
Options
You may also be interested in
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Separate main bonding to outbuilding

Former Community Member
Former Community Member
Hi, I just wanted people’s thoughts on this please.

I have been to a job with a TN-S supply. A sub main feeds a separate building with an SWA, the armour being used as the CPC. I have calculated the armour has not the additional cross sectional area to used as the required main bonding. I understand from GN8 that the main bonding needs to be extended to the building as specified in size by BS7671. I realise that this main bond will run from the MET to the Earth marshalling terminal in the second building. My question is this:

The SWA is buried and cannot be dug up (well easily). There is a second duct that runs between the buildings which is empty, but it follows a different route to the SWA. I seem to remember reading that it is best to run a separate bonding cable in close proximity to the existing SWA, am I correct or did I dream this? Is it advisable not to run the additional cable via a different route? If so, my only option will be to TT the second building.


Thanks in advance.


KS
Parents
  • Former Community Member
    0 Former Community Member
    That is nowhere near a domestic supply BOD. But you are trying to wind me up! 


    Not sure where domestic supply gets a mention in the OP though..............


    Admittedly my real life example is indeed a domestic albeit a large house where the DNO took the incoming service straight into the cellar into a 400 A cut-out and downrated the fuses. The installer assumed that as 100 A fuses, 10 mm2 would do. Unfortunately for him the Reg refers to the incoming neutral size, not that of the cut-out fuse. Quite an expensive job for him to rectify. 


    I did suggest that he could ask the DNO to do what they normally do and terminate their 185 mm2 just outside the property and joint to 35 mm2 and take into the property to a 100 A cut-out. Unfortunately the owner had just spent a fortune on red tarmac so he wasn't going to allow a patch up job in it. Besides which he paid a lot of money to get the HV line and Tx moved out of view, hence the need for 185 mm2 due to distance. Plus he didn't want his £500k+ of wine/port disturbed.


    Whilst I note that 10 mm2 would have been adequate with the second option and compliant, the "as installed" did not comply. As to the difference in reality could be argued at length, it is a Reg and Table 54.8 still applies. 


    No amount of experience or arguments can alter that Reg requirement...................... Unless you were to change the earthing arrangement and go TT of course............


    Regards


    BOD


Reply
  • Former Community Member
    0 Former Community Member
    That is nowhere near a domestic supply BOD. But you are trying to wind me up! 


    Not sure where domestic supply gets a mention in the OP though..............


    Admittedly my real life example is indeed a domestic albeit a large house where the DNO took the incoming service straight into the cellar into a 400 A cut-out and downrated the fuses. The installer assumed that as 100 A fuses, 10 mm2 would do. Unfortunately for him the Reg refers to the incoming neutral size, not that of the cut-out fuse. Quite an expensive job for him to rectify. 


    I did suggest that he could ask the DNO to do what they normally do and terminate their 185 mm2 just outside the property and joint to 35 mm2 and take into the property to a 100 A cut-out. Unfortunately the owner had just spent a fortune on red tarmac so he wasn't going to allow a patch up job in it. Besides which he paid a lot of money to get the HV line and Tx moved out of view, hence the need for 185 mm2 due to distance. Plus he didn't want his £500k+ of wine/port disturbed.


    Whilst I note that 10 mm2 would have been adequate with the second option and compliant, the "as installed" did not comply. As to the difference in reality could be argued at length, it is a Reg and Table 54.8 still applies. 


    No amount of experience or arguments can alter that Reg requirement...................... Unless you were to change the earthing arrangement and go TT of course............


    Regards


    BOD


Children
No Data

Community Rules & Guidelines