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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?
Yes, the requirements for sizing of main protective bonding conductors seems to be a rather blunt instrument. A TT installation with a 2.5 earthing conductor sized using the adiabatic would require a 6mm MPB. The same installation with an earthing conductor selected on the basis of table 54.1 where the conductor has no protection against mechanical damage or corrosion and therefore needs to be 25mm2 would have a 16mm2 MPB. On the other hand, where the risk of diverted neutral currents exist on a similar installation with a PME terminal, the MPB can be as little as 10mm2.
Yes, the requirements for sizing of main protective bonding conductors seems to be a rather blunt instrument. A TT installation with a 2.5 earthing conductor sized using the adiabatic would require a 6mm MPB. The same installation with an earthing conductor selected on the basis of table 54.1 where the conductor has no protection against mechanical damage or corrosion and therefore needs to be 25mm2 would have a 16mm2 MPB. On the other hand, where the risk of diverted neutral currents exist on a similar installation with a PME terminal, the MPB can be as little as 10mm2.
