Floating 90v AC

Hello All,

I have a strange issue.

I have a double insulated - no earth, phone charger. On one circuit in the house there is about 90V AC between the outer case of the USB plug and earth, earth in the socket or to a water pipe. This is enough to tingle the skin. On all other circuits it is fine. This is reproducible with two different chargers.

There is also enough on the TV aerial connector to feel a little belt.

My questions are therefore -

How is this even possible? I could understand if there was an earth core which was in contact with the live - but just live and neutral going through a rectifier and transformer?

How do I go about tracking down when this leakage is coming from?

Thank you.

Just to add - the TV signal goes through a mains powered amplifier.

EMF1 said:

Hello All,

I have a strange issue.

I have a double insulated - no earth, phone charger. On one circuit in the house there is about 90V AC between the outer case of the USB plug and earth, earth in the socket or to a water pipe. This is enough to tingle the skin. 

Click to expand...

I am assuming what you refer to as the outer case of the USB plug is a non-conductive, plastic-type enclosure? If so you are not reading anything between anywhere. To measure a potential difference you require two points to put your meter probes onto, from what I read you have one probe on electrical earth and the other probe not connected to anything with a conductive surface, (outer case of USB PSU), therefore it is just floating open circuit with no means for your meter to calculate anything of any significance.  

Doc H.

It's not uncommon to be able to feel a "tingle", from mains powered double insulated items, it's usually completely harmless and is due to capacitive coupling.

The difference you see in different rooms is most likely to be due to the environment there, such as type of floor you are standing on.

As regards meter readings, if you are using a digital multi-meter, with a high input impedance, the same applies, The leads and probes and anything touching them can act similarly to a radio antenna, picking up electromagnetic radiation from nearby sources and giving a misleading and completely meaningless display.  

In the very best situation you have a series circuit comprising the capacitance of your device and the  (unknown) input impedance of your meter to ground.