What does happen if neutral conductor is cut or broken? Then what should be predicting the necessary measures to prevent cutting the neutral conductor?

mapj1:

In a single phase system, if the circuit is carrying current and is suddenly open circuit, then like opening a switch, all the voltage appears across the break, and no volts across the load - but now both sides of the load are at the live voltage, so although it is off, it is not safe to stick fingers in!


In a 3 phase system, the neutral only carries the difference of the 3 phases, so if the load is well balanced, then you can take the neutral away, and nothing much happens, until you change the load on 1 phase - then the phase to phase voltages are divided unequally and you may see one load get an under voltage and 2 get an over voltage, but which and by how much depends on the load imbalance. As fuses then blow on the overvolted phase this may get quite pretty, as switching one load off can make 1/3 of the lamps things first go dim, while all the others go bright, then some of them go off, and others that were dim then brighten up and then it all goes off, if you are lucky, with only a modest bang, and a large bill for new lamps.


Neutral to earth shorts are  harder to detect, as when all is well they are at more or less the same voltage. But, RCDs see the imbalance in current in the L and N as a fault, and pop off, but only when the fault loop is low enough resistance, so not always, sometimes in a load dependent way  (not always your load though)- as that alters the neutral currents, and so  the the voltage drop.

 

mapj1:

In a single phase system, if the circuit is carrying current and is suddenly open circuit, then like opening a switch, all the voltage appears across the break, and no volts across the load - but now both sides of the load are at the live voltage, so although it is off, it is not safe to stick fingers in!


In a 3 phase system, the neutral only carries the difference of the 3 phases, so if the load is well balanced, then you can take the neutral away, and nothing much happens, until you change the load on 1 phase - then the phase to phase voltages are divided unequally and you may see one load get an under voltage and 2 get an over voltage, but which and by how much depends on the load imbalance. As fuses then blow on the overvolted phase this may get quite pretty, as switching one load off can make 1/3 of the lamps things first go dim, while all the others go bright, then some of them go off, and others that were dim then brighten up and then it all goes off, if you are lucky, with only a modest bang, and a large bill for new lamps.


Neutral to earth shorts are  harder to detect, as when all is well they are at more or less the same voltage. But, RCDs see the imbalance in current in the L and N as a fault, and pop off, but only when the fault loop is low enough resistance, so not always, sometimes in a load dependent way  (not always your load though)- as that alters the neutral currents, and so  the the voltage drop.