IEC 60364 Table 48A

The thing is, looking at your graphic, I wonder if any copper is really saved. All the copper that goes into bonding everything together locally could go into a larger CPC whereby touch voltage is reduced in addition to disconnection times via fuses.

Don't forget that bonding does a lot more than just protect against faults within the location/installation. Hazardous voltages can be imported from outside the location/installation and increasing the size of your own c.p.c.s will do little to help that.


The classic for bathrooms (think pre-combi days) is a vented hot water system, insulated from the cold water bonding by a plastic heater cistern, but connected to the exposed-conductive-parts of the immersion heater (usually in a cupboard off the back bedroom). A fault on the immersion - outside the bathroom - traditionally with up to a 5s disconnection time (as fixed equipment) puts the touch voltage directly between the hot and cold taps in the bathroom. (Hence we still require supplementary bonding in bathrooms unless such things cannot happen).


Likewise, for installations, a fault in an adjacent installation but with shared metallic pipework, or the much quoted open-PEN fault on PME supplies. Or for the more exotic, those near to electrified railways lines, where the diverted return traction current can create considerable potential differences in Earthing systems.


Then there's bonding for functional rather than safety considerations - have a read of BS EN 50310 (Application of equipotential bonding and earthing in buildings with information technology equipment) for the lengths some go to to ensure that data or communication signals aren't messed up by differences in earth potentials.


  - Andy.

The thing is, looking at your graphic, I wonder if any copper is really saved. All the copper that goes into bonding everything together locally could go into a larger CPC whereby touch voltage is reduced in addition to disconnection times via fuses.

Don't forget that bonding does a lot more than just protect against faults within the location/installation. Hazardous voltages can be imported from outside the location/installation and increasing the size of your own c.p.c.s will do little to help that.


The classic for bathrooms (think pre-combi days) is a vented hot water system, insulated from the cold water bonding by a plastic heater cistern, but connected to the exposed-conductive-parts of the immersion heater (usually in a cupboard off the back bedroom). A fault on the immersion - outside the bathroom - traditionally with up to a 5s disconnection time (as fixed equipment) puts the touch voltage directly between the hot and cold taps in the bathroom. (Hence we still require supplementary bonding in bathrooms unless such things cannot happen).


Likewise, for installations, a fault in an adjacent installation but with shared metallic pipework, or the much quoted open-PEN fault on PME supplies. Or for the more exotic, those near to electrified railways lines, where the diverted return traction current can create considerable potential differences in Earthing systems.


Then there's bonding for functional rather than safety considerations - have a read of BS EN 50310 (Application of equipotential bonding and earthing in buildings with information technology equipment) for the lengths some go to to ensure that data or communication signals aren't messed up by differences in earth potentials.


  - Andy.