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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
    Yes the MET could be up to 18.5v relative to the star point earth back at the substation.

    but I am referring to the potential you can measure at the origin of the installation i.e. from the Neutral to the MET. 

    In a PME TNC-S the voltage drop on the neutral supply cable will appear as small potential differences between the various multiple earths.

    so the N - E potential at the installation origin will be close to zero (only the voltage drop through the meter N and the earthing conductor).  

    This does presume zero current in the earth but since that should be minimal (except in fault conditions) the voltage drop in the earth path will be negligible.

    It also assumes equal conductor size for Line and Neutral, so for PME the parallel paths via the Neutral conductor and through the earth will reduce the voltage drop on the neutral side a bit.



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  • 0
    Yes the MET could be up to 18.5v relative to the star point earth back at the substation.

    but I am referring to the potential you can measure at the origin of the installation i.e. from the Neutral to the MET. 

    In a PME TNC-S the voltage drop on the neutral supply cable will appear as small potential differences between the various multiple earths.

    so the N - E potential at the installation origin will be close to zero (only the voltage drop through the meter N and the earthing conductor).  

    This does presume zero current in the earth but since that should be minimal (except in fault conditions) the voltage drop in the earth path will be negligible.

    It also assumes equal conductor size for Line and Neutral, so for PME the parallel paths via the Neutral conductor and through the earth will reduce the voltage drop on the neutral side a bit.



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