I got a Question to bounce back with if you don't mind... 1/  WHY "between conductors" and not ground? Is that the 3 phase business and balanced conductors phase and out of phase ??

Indeed - a.c. comes in a number of varieties - for example you can have 230/400V 3-phase where each line is 230V above Earth or Neutral but there's 400V between any two lines, or 230/460V "split phase" (or 115V-0-115V used on industrial hand tools). Even with d.c. you can have +ve, 0V and -ve rails- e.g. +12V/0/-12V giving 24V between the two outer lines.

Most of the time when we're considering electric shock it's under single fault conditions where a line conductor comes into contact with something that can be touched (typically an exposed-conductive-part) - in those cases the voltage between lines is pretty irrelevant - as it's just the voltage to Earth that's  imposed on the victim (or a proportion of it). Direct contact with two different lines simultaneously is normally prevented by basic insulation (or enclosures etc) and would require multiple simultaneous faults to allow it to happen - which mostly so unlikely we can ignore the possibility.. The voltage between lines only becomes significant where someone could easily touch two different lines simultaneously - that shouldn't happen in LV systems, but can sometimes be a risk in some ELV systems where basic insulation might be omitted - think of some of those ELV lighting system where light fittings are suspended from a pair of bare wires stretched between two walls.

The factor between voltages between lines and between one line an Earth on the common 3-phase a.c. system is √3 (or about 1.73) - which (with a bit of rounding off) is what you see between the stated limits for LV systems - so maybe think about it as deciding on a single voltage limit that a victim might be exposed to, but then writing it down in a way that's recognisable both to those doing single phase and those doing 3-phase work.

   - Andy.

I got a Question to bounce back with if you don't mind... 1/  WHY "between conductors" and not ground? Is that the 3 phase business and balanced conductors phase and out of phase ??

Indeed - a.c. comes in a number of varieties - for example you can have 230/400V 3-phase where each line is 230V above Earth or Neutral but there's 400V between any two lines, or 230/460V "split phase" (or 115V-0-115V used on industrial hand tools). Even with d.c. you can have +ve, 0V and -ve rails- e.g. +12V/0/-12V giving 24V between the two outer lines.

Most of the time when we're considering electric shock it's under single fault conditions where a line conductor comes into contact with something that can be touched (typically an exposed-conductive-part) - in those cases the voltage between lines is pretty irrelevant - as it's just the voltage to Earth that's  imposed on the victim (or a proportion of it). Direct contact with two different lines simultaneously is normally prevented by basic insulation (or enclosures etc) and would require multiple simultaneous faults to allow it to happen - which mostly so unlikely we can ignore the possibility.. The voltage between lines only becomes significant where someone could easily touch two different lines simultaneously - that shouldn't happen in LV systems, but can sometimes be a risk in some ELV systems where basic insulation might be omitted - think of some of those ELV lighting system where light fittings are suspended from a pair of bare wires stretched between two walls.

The factor between voltages between lines and between one line an Earth on the common 3-phase a.c. system is √3 (or about 1.73) - which (with a bit of rounding off) is what you see between the stated limits for LV systems - so maybe think about it as deciding on a single voltage limit that a victim might be exposed to, but then writing it down in a way that's recognisable both to those doing single phase and those doing 3-phase work.

   - Andy.