Hello everyone!
I have two 5V wall connected power supplies with a USB output, one rated 1A and the other 2A.
I use them for powering breadboards to test circuits.
I notices that with both of them, If I connect an LED to the positive rail and touch its cathode with my finger, It is turning on slightly.
Same goes for connecting the cathode of the LED to the negative rail and touch its anode with my finger.
These don't have an earthing connection, and they are similar to a phone charger as you can see in the picture attached.
Does it mean that these are not mains isolated? What can be the dangers of it?
Thank's in advance,
128ITSH

 

It sounds like this is the leakage of the mains through the stray capacitance within the wall wart. This is normal. The current is very small and is not harmful to people but may be sufficient to dimly light an LED.

 

It sounds like this is the leakage of the mains through the stray capacitance within the wall wart. This is normal. The current is very small and is not harmful to people but may be sufficient to dimly light an LED.

Thank's for the clarification. I'm less worried of using these supplies now.

 

Unplug the power supply and turn to the range 20MΩ with the multimeter, and the two probes connected to the Gnd pin and each pin of mains, if the meter has shows any values then it is un-isolation and it is also could be had leakage, if the values too small the turn the range to smaller as 2MΩ

 

Unplug the power supply and turn to the range 20MΩ with the multimeter, and the two probes connected to the Gnd pin and each pin of mains, if the meter has shows any values then it is un-isolation and it is also could be had leakage, if the values too small the turn the range to smaller as 2MΩ

Unfortunately my meter has a max range of 2MΩ, testing with this range doesn't show any value so it's probably isolated.
That's a good tip for the future anyway, thank you.

 

While using those wall warts keep in mind that many of them are not properly designed and manufactured with safety as the #1 goal. Try not to make yourself a return path to ground for any leakage that develops and test occasionally to see that ground leakage current is below a few milliamps.

If your wall wars were made by a reputable manufacturer and has recognized safety marks, and is not a counterfeit, you need not be so cautions.

 

The problem with these smps units is they have 1nF suppression capacitor and 10Meg resistor in parallel , and they join the mains Negative and output Negative together, you can open them up and remove them.