IEC 60364 Table 48A

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


Oh no saving at all really. The big problem with your idea is that is that the CPC to the light above the sink does not  go to the taps at all, unless you bond it, and the 'equipotential'  idea here was that during fault it all flashed live together, and the hapless user feels no shock because he and everything he can possibly touch is at the same voltage, so you can afford an upper limit of 5 seconds for the fuse to blow. Bit like the bird on the LV cable. Some single phase O/H TT for you here.

Note that this pole could not be made PME without some changes to the cable arrangement.






Note I say 5 seconds, not 0.4 - that faster limit applied to the ccts in the bathroom, but not to everything sharing the same CPC and plumbing, so a fault in the bedroom, left  of picture, ( note the bond to the metal bits of the fire place - did anyone ever do that, really ?) could perhaps take anything up to 5 seconds to clear with extension leads and a defective heater or something,  - and the whole bathroom may go up with it as well, as the radiator pipes are shared. Pity about the poor old window cleaner touching the same live for 5 seconds window frames from outside of course....


And the fact is that a new installation probably met all the resistance test limits for all of about a week until someone changed the taps, or the radiator or something  led to the whole concept falling to one side a bit.

And it is no damn good having live taps and all that jazz if you are standing on a modern concrete floor either. The traditional floor boards  with a 2 foot airgap work really well but solid floors downstairs are a bit more variable.

So now we drop the EEB, fit an RCD to get the breaking time down for all circuits, not just bathrooms, and it is just called ADS.

Mike.

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


Oh no saving at all really. The big problem with your idea is that is that the CPC to the light above the sink does not  go to the taps at all, unless you bond it, and the 'equipotential'  idea here was that during fault it all flashed live together, and the hapless user feels no shock because he and everything he can possibly touch is at the same voltage, so you can afford an upper limit of 5 seconds for the fuse to blow. Bit like the bird on the LV cable. Some single phase O/H TT for you here.

Note that this pole could not be made PME without some changes to the cable arrangement.






Note I say 5 seconds, not 0.4 - that faster limit applied to the ccts in the bathroom, but not to everything sharing the same CPC and plumbing, so a fault in the bedroom, left  of picture, ( note the bond to the metal bits of the fire place - did anyone ever do that, really ?) could perhaps take anything up to 5 seconds to clear with extension leads and a defective heater or something,  - and the whole bathroom may go up with it as well, as the radiator pipes are shared. Pity about the poor old window cleaner touching the same live for 5 seconds window frames from outside of course....


And the fact is that a new installation probably met all the resistance test limits for all of about a week until someone changed the taps, or the radiator or something  led to the whole concept falling to one side a bit.

And it is no damn good having live taps and all that jazz if you are standing on a modern concrete floor either. The traditional floor boards  with a 2 foot airgap work really well but solid floors downstairs are a bit more variable.

So now we drop the EEB, fit an RCD to get the breaking time down for all circuits, not just bathrooms, and it is just called ADS.

Mike.