Only shorts via earth affect the rating of the earth conductor, which is what I think you are sizing adiabatically in this example.
Also L-N faults have no upper limit to the breaking time, except that set by cable failure.
L-E faults need to be off in half a heart beat for very good safety of life reasons.
DZ is reminding us to look also at the extreme high Zs case, where an L-E short does pull up the earth voltage to near live but does not draw enough current to blow the supply fuse in any usefully short time. The opposite case to the adiabatic how where the limit is "how hot is my cable for a dead short close by the Xformer ? "
300mA RCD 1/3 second delay or 100ma 1/10 second delay at the origin usually fixes.
Only shorts via earth affect the rating of the earth conductor, which is what I think you are sizing adiabatically in this example.
Also L-N faults have no upper limit to the breaking time, except that set by cable failure.
L-E faults need to be off in half a heart beat for very good safety of life reasons.
DZ is reminding us to look also at the extreme high Zs case, where an L-E short does pull up the earth voltage to near live but does not draw enough current to blow the supply fuse in any usefully short time. The opposite case to the adiabatic how where the limit is "how hot is my cable for a dead short close by the Xformer ? "
300mA RCD 1/3 second delay or 100ma 1/10 second delay at the origin usually fixes.
