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

Alasdair Anderson:

Alex,

I am afraid your question is too ambiguous.

Are you referring to a single phase (live + neutral) circuit, a final circuit, a distribution circuit, a three phase + neutral circuit/distribution circuit.  The outcome could be very different in each case.

Next are you meaning a simple break in the conductor (broken wire) or a cut which might also be introducing an earth fault? In which case is it downstream of an RCD?

The answer could be anything from "the circuit stops working" through to "there is a loud bang as the protection operates".

If you could explain a bit more, possibly even your reason for asking, you may get any number of people providing answers to help you out.

Best wishes,

Alasdair

(Postscript during editing time: I have just realised that your question actually sounds a bit like a homework question - if it is then I should point out that this forum is not intended as a source of answers for homework, but you will find any number of contributors willing to provide exhaustive answers in order to show up teachers/lecturers....)

Please tell me if this happen in LV electrical installation.

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.

 

jcm:

... sure enough whole postcode for my area was off, they seemed to break the post code  into blocks but all was off , they said it was equipment fault , power back on after about 2 hours.

jcm:

. . . I got the torch and switched it on , lights came on , one minute later darkness, this time RCD was up/on but no supply, noticed all the street lights were off the whole countryside was off . Candles and after while looked up on laptop to see any information , sure enough whole postcode for my area was off, they seemed to break the post code  into blocks but all was off , they said it was equipment fault , power back on after about 2 hours . Why did this fault trip my main RCD before the power failure I don't know.

jcm