Ah, but now imagine it is fed by that open wire single phase TT supply, with or without bird.Now it all floats up to near mains voltage, and sits there for quite a while until something trips. Now I think, if you are in the bathroom you'd like the taps bonded to the towel dryer and so on.
And personally, I'd not want to 'upgrade' to a PME like arrangement either lower Zs or not, as a stray tree branch could easily break just one line and leave you with a very hot earth indeed. Neither will the DNOs - round here they insist to convert to a sort of insulated twisted pair they call ABC (Aerial Bundled Cable) before PME is even an option.
As a historical note in that era that the bonding came in, the TT main cut out would probably open contacts based on CPC to electrode voltage rise, not current balance, so not as a modern RCD or GFCI. But from 1985 they were no longer accepted and the RCD type dominated . Between 1981 to 1985 RCDs were preferred but both methods were acceptable on new work where the earth electrode was not man enough to blow a fuse in a few seconds, and that would be most domestic with the then new style plastic water pipes to be honest.
Yeh, but the fire was started by a propane torch not an electrical arc. Why worry about electrical arcs when the fire has already been started by another cause? Illogical.
Edit, add.
In the U.K. we have the wonderful 13 Amp. plug made to B.S. 1363. Have you ever heard of it? It contains a fuse. The fuse rating can popularly be either 3 Amp or 13 Amp, but other sizes are available like 5 Amp or 10 Amp. Flexes are protected by these fuses which are less in value than the 20 Amp circuit breakers referred to in the dated video.
Z.
Illogical indeed, but sadly this was enough to get AFCIs taken seriously.
Of course I've heard of BS 1363 plugs. AFCIs were supposed to to mimic their their ability of clearing flex faults rather quickly.
Yeh, but the fire was started by a propane torch not an electrical arc. Why worry about electrical arcs when the fire has already been started by another cause? Illogical.
Edit, add.
In the U.K. we have the wonderful 13 Amp. plug made to B.S. 1363. Have you ever heard of it? It contains a fuse. The fuse rating can popularly be either 3 Amp or 13 Amp, but other sizes are available like 5 Amp or 10 Amp. Flexes are protected by these fuses which are less in value than the 20 Amp circuit breakers referred to in the dated video.
Z.
Illogical indeed, but sadly this was enough to get AFCIs taken seriously.
Of course I've heard of BS 1363 plugs. AFCIs were supposed to to mimic their their ability of clearing flex faults rather quickly.
To quick? These can not tell the difference between sparks and LED lights, motors starting, bulbs burning out, switch mod power supplies, microwave ovens, ham radios, TVs, the list of devices and conditions which trips them gets its own library.
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.
but IMO I think bonding to the MET vs pipe bonding in every room would accomplish the same.
But in a fault situation where lots of current is flowing in the cpc but little current is flowing in the bonding conductor (just the 50mA or whatever flowing between two hands touching two things) then a bond to MET as opposed to a bond to the cpc near the fault will add the voltage drop along the cpc from MET to fault to the total touch voltage.
