What happens when the neutral conductor is open circuited

This occurs due to either of the two reasons  i.e. firstly due to  poor  contact at a  jumper connection,
Secondly, the supply being resumed to an installation without  taking care to put the neutral link back normal. Under such conditions, the neutral will assume a potential determine by the load in each of the phase because it is free to move anywhere within the triangle formed by the 3 phase potential ABC,and is no longer tied to the earthed star of the transformer.  (Star point of star winding of distribution transformer is solidly connection to keep the potential zero at the star point. The neutral conductor of 3 phase 4 wire distribution line is connected to star point of star winding of the distribution transformer). Such a neutral is called 'floating'.
        
     Fig. A & B provide balanced load on  the three phase  i.e.230 volt between each phase and neutral.
     Fig. C there are two equal load between line A & B. The floating neutral will now be at point 'Y' and the voltage between neutral and line A B C will be 200,200 & 346 volts. In such cases, there is every possibility of large number of lamps being burnt out if by mistake, installation neutral is not solidly connected  to the  incoming  supply or if there is a  poor contract in one of  the mechanical connectors on  the neutral line.






N.B:-  ABC is a RYB phase, N is a Neutral,  L  is Load, X and Y is a Floating Neutral point. 



Fig.D.  If the floating  neutral is at point 'X' , The voltage between neutral and the different phase
will very causing danger to lamps and other electrical appliances. 

Location: India

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