# AC voltage on the outside surface of micro USB charger cable

My micro USB mobile charge cable is having about 98V AC voltage on the outside surface. (PFA measurement image. The black probe is connected to the Power socket Ground port. I could not take the whole picture with one hand) The DC voltage is about 0.02V w.r.t. the Ground.

Online QA websites suggested that this may be due to a faulty charging adapter. But I have inserted another micro USB cable into the same adapter and it showed only about 1.5V AC on the surface.

Then, I took another charging adapter and the same thing happened. The first cable showed about 47V AC and the second one only 1.3V.

Thus, it seems that it is not the fault of the charging adapter. My electrical knowledge is not very good. Can someone explain why is this happening?

Edit: Just to clear the confusion I created with the example of 2 wires, actually the AC voltage is always there at the adapter output. I have put my multimeter probe on the metal just inside the adapter (without touching any of the 4 wires inside). and the inside was about 98V AC. the 2nd cable's both bare end metals were not continuous. so, the voltage didn't appear on the micro USB end.

So, my question is, why is the AC voltage appearing and does this mean that the adapter has gone bad?

• @AdamLawrence The black probe is connected to the Power socket Ground port. That's why I wrote that the voltage is w.r.t. the ground. I could not take the whole picture with one hand :P Commented Dec 4, 2018 at 16:39
• Do you measure continuity (0 ohms) between the exposed metal on both ends of the cable (after removing it from the charger of course)? Commented Dec 4, 2018 at 16:51
• @AdamLawrence The cable showing high AC voltage (50-100v) is passing continuity test (resistance is about 2.5 ohm, my multimeter buzzes continuity buzzer if resistance is less than 50 ohm). But the cable showing low AC voltage (1.5 v) is not passing the continuity test. I guess this is the reason the 2nd cable is not getting the AC voltage at the micro USB connector head because the two end metals are not continuous. But the 1st cable is getting the AC voltage from the USB end. Commented Dec 4, 2018 at 17:06
• But can I say that the charging adapter is bad from this? because one of the 2 adapters is the original mobile manufacturer's charger. Also, the shock is very mild at the micro USB end but the voltage is quite high (50-100 v). Why is this? Commented Dec 4, 2018 at 17:08
• You might want to try it with, say, a 470K resistor across the multimeter. You may be measuring the noise coupling into the shield connection without direct contact. If you measure it with a sufficiently high impedance, the voltage can still be high, but with any load it will drop quickly to zero. (If you see >5VAC with a 470K load, then I'd start to worry.) Commented Dec 4, 2018 at 18:43