Light reading

MrJack96:

Yeah thank you I thought that would be the case the extra resistance the earth would limit current flow meaning the parts extraneous conductive parts within the installation would raise to near 230v with respect to the earth outside. 

I think it's better to say that "extra resistance of the earth might limit current flow". As Andy says, the current may well divert down a very low impedance cast iron gas or water pipes !


In fact, things are slightly more complicated especially where the broken PEN conductor is in a three-phase cable. In this case, the L-N voltage may not always drop - it might well increase above Uo, in theory as much as about 350 V (which is a little counter-intuitive, but entirely possible with the right power factor loads on each phase).


And regardless of this, it takes only a few 10s of mA to kill someone, so even of the loads appear not to be working, because not enough current may flow, there may well still easily be enough to cause serious harm, or at worst kill someone.

MrJack96:

Yeah thank you I thought that would be the case the extra resistance the earth would limit current flow meaning the parts extraneous conductive parts within the installation would raise to near 230v with respect to the earth outside. 

I think it's better to say that "extra resistance of the earth might limit current flow". As Andy says, the current may well divert down a very low impedance cast iron gas or water pipes !


In fact, things are slightly more complicated especially where the broken PEN conductor is in a three-phase cable. In this case, the L-N voltage may not always drop - it might well increase above Uo, in theory as much as about 350 V (which is a little counter-intuitive, but entirely possible with the right power factor loads on each phase).


And regardless of this, it takes only a few 10s of mA to kill someone, so even of the loads appear not to be working, because not enough current may flow, there may well still easily be enough to cause serious harm, or at worst kill someone.