VOLTAGE BETWEEN THE GENERAL MASS OF EARTH AND A PME NEUTRAL/EARTH

John Peckham:

Thank you for your input so far.


Zoom


You say you have a VOELCB, is that fitted or on the shelf? If it is fitted do you experience any nuisance tripping if so how frequent? 


There is an old publication produced by Crabtree called: "The Protection of Domestic and Industrial Installations" which covers the use of V.O.E.L.C.B.s in great detail. Publication No. B1181.




I have been carrying out some tests on my collection of VOELCBs from my black museum. I have also been scrutinizing the BS 842 which is still a current (excuse the pun) standard for VOELCBs.


I am not getting this divergence of potential between Neutral and the true mass of earth under FAULT FREE CONDITIONS. I do get it under various fault conditions where it would be desirable for the VOELCB to trip.The required current to trip the device is dependent on the voltage between the mass of earth and the frame terminal of the device. How was this test carried it the good old days given the much quoted voltage of 50V is frequently refer ed to as the required test voltage? Or is an early example of making up test results for the test certificate? If 50V was applied directly between the F and E terminals it would trip in mighty quick time as my experiments get my collection of devices to trip at 12V when applied directly to the coil! I killed one of my collection when I accidentally applied the test voltage with my Variac at the wrong end of the scale, the coil is now open circuit.




R E P L Y>>>>>>>>>>>>>>


Hello John,

                      I do not have a V.O.E.L.C.B. installed anywhere at home. I do remove them from older installations. I partially dismantle them and service them just for fun and add them to my own collection.


Please note that a row of country terraced houses back in the 70s may have had a V.O.E.L.C.B. installed in each house. If the common metal gas pipe serving each house had a Voltage rise on it from house A, then house Bs V.O.E.L.C.B. could trip off, but the fault could still prevail on the gas pipe, so a minor shock risk could exist in house B even with its own electrical supply cut off, in certain situations. A person could feel tingles if they touched both the metal gas pipe and a better earthed metal water pipe.


Nuisance tripping did occur years ago with these devices.


The E.60 device had an E.L.  tripping coil of impedance 500 Ohms and  a minimum tripping current of 35mA.


The V.O.E.L.C.B. was tested with a 45 Volt a.c.  supply connected between N and E. A short circuit rated 750VA double wound step down transformer was used to provide the test supply of 45 Volts..


Z.



 

John Peckham:

Thank you for your input so far.


Zoom


You say you have a VOELCB, is that fitted or on the shelf? If it is fitted do you experience any nuisance tripping if so how frequent? 


There is an old publication produced by Crabtree called: "The Protection of Domestic and Industrial Installations" which covers the use of V.O.E.L.C.B.s in great detail. Publication No. B1181.




I have been carrying out some tests on my collection of VOELCBs from my black museum. I have also been scrutinizing the BS 842 which is still a current (excuse the pun) standard for VOELCBs.


I am not getting this divergence of potential between Neutral and the true mass of earth under FAULT FREE CONDITIONS. I do get it under various fault conditions where it would be desirable for the VOELCB to trip.The required current to trip the device is dependent on the voltage between the mass of earth and the frame terminal of the device. How was this test carried it the good old days given the much quoted voltage of 50V is frequently refer ed to as the required test voltage? Or is an early example of making up test results for the test certificate? If 50V was applied directly between the F and E terminals it would trip in mighty quick time as my experiments get my collection of devices to trip at 12V when applied directly to the coil! I killed one of my collection when I accidentally applied the test voltage with my Variac at the wrong end of the scale, the coil is now open circuit.




R E P L Y>>>>>>>>>>>>>>


Hello John,

                      I do not have a V.O.E.L.C.B. installed anywhere at home. I do remove them from older installations. I partially dismantle them and service them just for fun and add them to my own collection.


Please note that a row of country terraced houses back in the 70s may have had a V.O.E.L.C.B. installed in each house. If the common metal gas pipe serving each house had a Voltage rise on it from house A, then house Bs V.O.E.L.C.B. could trip off, but the fault could still prevail on the gas pipe, so a minor shock risk could exist in house B even with its own electrical supply cut off, in certain situations. A person could feel tingles if they touched both the metal gas pipe and a better earthed metal water pipe.


Nuisance tripping did occur years ago with these devices.


The E.60 device had an E.L.  tripping coil of impedance 500 Ohms and  a minimum tripping current of 35mA.


The V.O.E.L.C.B. was tested with a 45 Volt a.c.  supply connected between N and E. A short circuit rated 750VA double wound step down transformer was used to provide the test supply of 45 Volts..


Z.