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Neutral Voltage Question

fiftyhertz
Hi all, 


Hoping someone can help with this, as it bothering me that I dont know this. 


This is quite tricky to explain without an image. Essentially, if we have a circuit supplying one luminaire. The line conductor has a voltage of 230v from earth potential supplying the light. To complete the circuit, on the return leg a neutral is required (<50v from earth potential). Where is the point where the neutral is no longer at mains voltage, is it at the neural terminals? 


Is it a case of the luminaire will "use up" the supplied mains voltage? 


Any assistance is appreciated. 


Thanks
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  • 0
    I am not aware of any DNO installing superconducting Neutrals ? so there will always be some potential difference between the various earths along a PME PEN (except when zero load).


    In the case of a reduced neutral the Line conductors should be sized for the full load on all three phases with an absolute maximum of 37 volt drop. 

    If only one phase is being fully loaded then the DNO has an undersized neutral and their design assumption is false in providing a reduced N.

    If the single phase only load is within the capacity of the half sized neutral then their will be a correspondingly lower drop on the one loaded Line.

    If the voltage drop on the neutral + the drop on the line exceeds 37v then the DNO is in breach of ESQCR.  Either because of undervoltage at full load or overvoltage at no load.


    In either case I don't see the N - E voltage at the origin of the installation exceeding this worst case figure of 18.5v.

    In all other situations the N - E voltage will be considerably less.
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  • 0
    I am not aware of any DNO installing superconducting Neutrals ? so there will always be some potential difference between the various earths along a PME PEN (except when zero load).


    In the case of a reduced neutral the Line conductors should be sized for the full load on all three phases with an absolute maximum of 37 volt drop. 

    If only one phase is being fully loaded then the DNO has an undersized neutral and their design assumption is false in providing a reduced N.

    If the single phase only load is within the capacity of the half sized neutral then their will be a correspondingly lower drop on the one loaded Line.

    If the voltage drop on the neutral + the drop on the line exceeds 37v then the DNO is in breach of ESQCR.  Either because of undervoltage at full load or overvoltage at no load.


    In either case I don't see the N - E voltage at the origin of the installation exceeding this worst case figure of 18.5v.

    In all other situations the N - E voltage will be considerably less.
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