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An interesting issue with a TT supply

Alan Capon
An interesting real life example of why you need double pole switching with a TT supply. The scenario is a small village with a few customers supplied by a single pole mounted transformer. 


We got a call from an electrician working in a property who had measured 400V phase to earth, 210V neutral to earth, and 241V phase to neutral, and was understandably worried. Any suggestions of what I tracked the fault down as? This can happen on any TT supply, but is fortunately very rare - I have come across it three times in 20 years. 


Regards,


Alan.
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    Looking at Davezawadi’s answer, it was an interesting problem. The earth fault meant that L3 to earth was only a handful of volts. All the phase to neutral voltages were correct, as were the phase to phase voltages, so everything worked normally. The advantage we had as the DNO, is that we had the ability to look at the whole village, and disconnect properties until we found out who had the problem. 


    Regards,


    Alan.
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  • 0
    Looking at Davezawadi’s answer, it was an interesting problem. The earth fault meant that L3 to earth was only a handful of volts. All the phase to neutral voltages were correct, as were the phase to phase voltages, so everything worked normally. The advantage we had as the DNO, is that we had the ability to look at the whole village, and disconnect properties until we found out who had the problem. 


    Regards,


    Alan.
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