3 core power cable leakage issue

[raman00084]

i am measuring 3 phase voltage using pic micro , for that i am scalling 440v to 1.5v using resister 2.2meg and 6.8k. every thing works fine i can see the 3 phase voltage on lcd
but if i disconnect 1 phase in the 3 core wire i can see some leakage voltage present the line tester glows bot very little current if i touch in hand no shock. my problem is adc reads that voltage as 260v and not coming to zero. if i use single wire for 3 phases no problem. how to solve this issue.

 

[treez]

but first, i need to know the setup, are you measuring the voltage at the output of a 3phase, 6 pulse rectifier?...and you have some capacitance across the lower sense divider resistor?
You disconnected a phase and the sensed voltage goes down?....well thats just normal

 

[raman00084]

no capacitor, you just try this take a 3 core wire connect one wire in hot line phase with the line tester test the other two lines in the cable the tester will glow the wires are open but still the tester will glow, if you touch no shock only little current.

 

[chuckey]

As you have a high input impedance capacitive cross talk could be causing this. Try putting a 220K across from your live end of 2.2M to earthy end of 6k8. It will demonstrate where the voltage is/is not coming from. The other questio0n is to what is your 3 PH referenced to? If its from a delta transformer, then the whole winding can float to any potential. It should be from a Y (star) transformer with the neutral point earthed as I suspect your "earthy" measuring point is actually earth.
Frank