What would a clean-sheet set of wiring regulations look like today?

In no particular order..
Assuming all countries got the same reset at the same time, an internationally agreed standard for plugs and sockets indoors and outdoors for a start then we could ditch the plug and socket regs. 
Probably higher voltages than 230, as nowadays really good insulation  (by the standards of the old sweats) is cheaper than copper and energy losses are a bigger consideration, so fewer wider spaced transformers would be good. 
Probably not bother with the bayonet lamp holder.
Compulsory all-pole Isolation immediately after metering points.
Double pole breakers.
Standardised Din rail terminal positions and breaker profiles.
No PME
Training on how to do decent diagrams
Insulation on the (full size?) earth cores of cables.

M.

mapj1 said:

No PME

I've never really understood what the alternatives are and how they are 'better', given that 'Earth' is everywhere, and phenomenally good by the cubic mile.

It feels as if the different factions make different assumptions about the natural spacings between electrical equipments, and the ease (lack of) 'earth' connections (and what they are trying to do/not-do with said connections).

It's all as \clear\ conductive as mud.

Three phase doesn't help .

Philip Oakley said:

I've never really understood what the alternatives are and how they are 'better', given that 'Earth' is everywhere, and phenomenally good by the cubic mile.

Agreed ... potentially with the consideration of 'assume TT but connect TN-S' might actually achieve better safety, but possibly with the downside of lack of selectivity pas a certain point in the distribution?

Philip Oakley said:

mapj1 said:

No PME

I've never really understood what the alternatives are and how they are 'better', given that 'Earth' is everywhere, and phenomenally good by the cubic mile.

Earth is good - the problem is getting a adequate connection to it (a square mile of contact would do nicely, but would be a tad inconvenient).

The main problem with PME is the -C- part of TN-C-S - i.e. they put N current down "earth" conductors, so if there's a problem at all you naturally end up with significant voltage differences between things that should by design be at the same potential.

TN-S is the obvious alternative. Although there have been some supply impedance earthed (IN-S?) suggestions that have the advantage that even during an earth fault event all the exposed-conductive-parts remain close to true earth potential - so ADS becomes a lot less critical.

  - Andy.

In a world where we only need 150mA to 'fast' trip a circuit RCBO, which can be backed up in case of failure by a time delay RCCB at the consumer unit (and possibly even a second one with a longer time delay at the meter!), do we really need the very low earth impedances of TN-S?

I suppose belt-and-braces, but I think a system created today would be essentially all RCBO, and TT might be optimum.
As noted above, install TN-S but assume TT?

In a world where we only need 150mA to 'fast' trip a circuit RCBO, which can be backed up in case of failure by a time delay RCCB at the consumer unit (and possibly even a second one with a longer time delay at the meter!), do we really need the very low earth impedances of TN-S?

I suppose belt-and-braces, but I think a system created today would be essentially all RCBO, and TT might be optimum.
As noted above, install TN-S but assume TT?

EIreland said:

do we really need the very low earth impedances of TN-S?

Earthing isn't just about ADS .. there's a bigger problem of trying to keep equipotentiality that spans into other areas - e.g. IT/comms systems, EMI and where SPDs can dump their unwanted surge currents into (and probably a few others too) - so a solid reliable earth is still good in my mind. Not least when you consider the potential unreliability of consumer's TT electrodes in the increasingly dry ground these days.

I still like the idea of IN-S - everything "earthed" is solidly connected together and to Earth, but earth fault currents are low, so large potential differences are mostly avoided. 

  - Andy.

Would IN-S take the form of a conventional earthing resistor at the transformer end?

Would it be possible to build a house wired as if it was a TT system which was connected to a TN-S distribution system through a suitable earthing resistor at or near the cut out?

For example, if we attached a local resistor to keep the resistance at ∼1Ω, we'd be able to limit fault currents to 230A or so.

If all circuits are fitted with 30mA RCBO and the system is backed up by a 100mA S-Type RCD (possibly Type B as a cheap way to gain some protection against blinding) then the adiabatic heating in an earth conductor would be more than less eliminated as an issue.

I make it about 8000A²s for a dead-short earth fault where the 30mA RCBO fails to operate and the S-Type opens at 150ms, which is well within the capability of 1mm² copper conductors, even in PVC.

Even if both the RCD and the RCBO fails (including on a big over-current), with a ∼1Ω earth resistance the fault would have to be passing 50A or so produce hazardous touch voltages. As the installation has a big chunk of resistance in hand, we could use the potential across the earthing resistor to trigger a time delayed solenoid with tens of volts to force contacts open and disconnect the supply. In essence a new take on the old "Voltage triggered earth leakage circuit breaker". The voltage would be large enough to avoid issues with RCD 'stickiness', and we could accept an opening time of about 300ms before a 1mm² XLPE conductor exceeds its acceptable temperature rise.

And if the TN-S connection fails open, the system still operates as a TT system with two levels of protection at <200Ω earth impedance from the local earthing rod.

This means it takes 3 failures to cause a sustained dangerous condition. The circuit RCBO must fail, the S-Type RCD must fail and either the TN-S must fail open or the ELCB must fail. 

or, the resistor might fail instead - 1 ohm carrying 230A for long enough to blow the company fuse will get quite warm:-)  unless its very big. 

M

Well, if we went down that road..... 

As far as I can tell, a BS88 Gg 100A fuse will blow at 230A (~50kW) in about 5 minutes. That implies a total power dispersal of 16MJ, or about the boiling of 7L of water, making allowance for some liquid being expelled.

Well assuming its outside adjacent to the cut out, you could have a sealed stainless steel water can with a burst disc and an old style kettle whistle mounted to the top! A cylinder say 12cm in diameter and 1m tall would hold more than enough!

The water won't start boiling for tens of seconds after the fault commences, and if the mechanical protection hasn't opened by then it probably never will do.