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 3 replies
  • Subscribers 32 subscribers
  • Views 458 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

Bonding Question

me1899
Hi All


Hope you are well - just looking for a bit of guidance on bonding on a job - schematic picture attached.


Basically, 200A head to busbar chamber (TNCS)


63A SPN switch fuse to Building 1 - a big metal shed - 35mm buried SWA 3 core. For main bonding, I understand I have to put 35mm bonds to metalwork. Incoming pipes are plastic. Will I need to bond the incoming BT? Single copper line off the road.


200A isolator to central plant room - 185m away with a 200A MCCB board. This is to feed 5 buildings inc. a 3 phase. Plant room will have an MCB board also for external lighting and air con units which will serve 2 buildings via buried refrigerant pipe. Also a booster pump with metal pipework which is plastic as it leaves/enters the room. Also a central TV/radio system to feed coax out to the 5 buildings fed from here.


As I understand, I need to do 35mm bonds for structure, air con, and also BT incomer and aerial. Believe latter two to be 6mm? Also supplementary 2.5mm bonds for pipes, pumps, metal door frames.


All 5 properties fed from plant room have 35 or 50mm feeds and I understand these all need 35 main bonds for structure, AC pipes (where fed from ac outdoor units at plant room). For coax and BT cables - 6mm bonds? 


In a nutshell - am I correct in my understanding of the bonding sizes, in particular  telecoms and BT feeds? Using combined CPC and bonding conductors. I tend to see 6mm for comms and TV stuff.


A sanity check would be very welcome.


Regards


Muhammad

 
 

446fc18f3228f993e9ad6284b8d5108f-huge-schem.png
Parents
  • 0
    Unfortunately I can't quite read your diagram.


    Double check the bonding size needed - I would have expected a 200A 3-phase supply to arrive on something like a 95mm² cable and presuming the CNE is the same size that would imply a more workable 25mm² bond according to table 54.8 (yours might validly differ though, or have more onerous network conditions).


    I don't every recall seeing a BT line being bonded - many (esp. overhead ones) won't have anything to bond and where an underground cable does have a metallic armour, I think it's more usual just to ensure that armour is covered/insulated so it can't be touched or introduce a potential into the installation, rather than bond it. You'd need the explicit consent of the cable's owner in any event (see reg 411.3.1.2) - which I suspect might not be forthcoming.


    I'm not sure where you get 6mm² bond size from - that's the minimum bonding size for non-PME systems or for connection of type 2 SPDs near the origin. The general minima for individual  protective conductors is 2.5mm² where mechanically protected or 4mm² otherwise - except that main bonding conductors will have to meet table 54.8 of course.


    Bonding metal door frames sounds suspect  - they're unlikely to be exposed-conductive-parts as defined (i.e. introducing a potential) and bonding them creates a significant risk to people just outside the building, especially during faults or open CNE conditions.


      - Andy.
Reply
  • 0
    Unfortunately I can't quite read your diagram.


    Double check the bonding size needed - I would have expected a 200A 3-phase supply to arrive on something like a 95mm² cable and presuming the CNE is the same size that would imply a more workable 25mm² bond according to table 54.8 (yours might validly differ though, or have more onerous network conditions).


    I don't every recall seeing a BT line being bonded - many (esp. overhead ones) won't have anything to bond and where an underground cable does have a metallic armour, I think it's more usual just to ensure that armour is covered/insulated so it can't be touched or introduce a potential into the installation, rather than bond it. You'd need the explicit consent of the cable's owner in any event (see reg 411.3.1.2) - which I suspect might not be forthcoming.


    I'm not sure where you get 6mm² bond size from - that's the minimum bonding size for non-PME systems or for connection of type 2 SPDs near the origin. The general minima for individual  protective conductors is 2.5mm² where mechanically protected or 4mm² otherwise - except that main bonding conductors will have to meet table 54.8 of course.


    Bonding metal door frames sounds suspect  - they're unlikely to be exposed-conductive-parts as defined (i.e. introducing a potential) and bonding them creates a significant risk to people just outside the building, especially during faults or open CNE conditions.


      - Andy.
Children
No Data

Community Rules & Guidelines