You cannot post a reply to this discussion. If you have a question start a new discussion
Bonding conductor sizes
Former Community Member
What is the reason for bonding conductors being sized according to the size of the supply neutral? I can see how earthing conductors / cpc’s are selected according to adiabatic considerations: making sure they can stand up to a fault. I understand that the bonding is to maintain an equipotential zone but how does the neutral csa and bonding csa relate to this?
Note that main bonding sizes only relate to the supply N for PME systems (or potentially PME systems) - for other systems (TT, true TN-S etc) they're related to the earthing conductor size & a simple minimum (6mm²) to cater for physical robustness & possible currents imported through extraneous-conductive-parts.
It's not only during broken CNE conditions that bonding conductors on PME systems may have to carry significant diverted N currents - bonding conductors (together with extraneous-conductive-parts running between installations) often form a parallel path to the supplier's CNE so will carry a proportion of the N current even under normal conditions. Looking at the sizes involved (in table 54.8) you might even get the impression that they're sized on the assumption that they'll be carrying only about half the installation's N current - which might suggest they're only really sized for normal conditions - rather than broken CNE events when a bonding conductor could easily be pressed into carrying the entire installation's N current (possibly more if several installations share the same extraneous-conductive-parts).
Note that main bonding sizes only relate to the supply N for PME systems (or potentially PME systems) - for other systems (TT, true TN-S etc) they're related to the earthing conductor size & a simple minimum (6mm²) to cater for physical robustness & possible currents imported through extraneous-conductive-parts.
It's not only during broken CNE conditions that bonding conductors on PME systems may have to carry significant diverted N currents - bonding conductors (together with extraneous-conductive-parts running between installations) often form a parallel path to the supplier's CNE so will carry a proportion of the N current even under normal conditions. Looking at the sizes involved (in table 54.8) you might even get the impression that they're sized on the assumption that they'll be carrying only about half the installation's N current - which might suggest they're only really sized for normal conditions - rather than broken CNE events when a bonding conductor could easily be pressed into carrying the entire installation's N current (possibly more if several installations share the same extraneous-conductive-parts).
