Sometime back, I bought a 12 V, 5 A SMPS from a electronics ship for audio amplifier. It was a class-2 SMPS with an earth pin. I used it as such with earth connection and an inductor was used in series with the output to remove any extra oscillations. Without the earth connection, it leaked current through its metal body and caused hum in the amplifier.

Recently, I bought another SMPS and I did the same procedure, but this time it started making some hum even after earthing. Then I found that connecting the 12 V output negative terminal and earth terminal of SMPS stopped the noise. I connected a 1 μF, 63 V capacitor between the negative output DC and earth and the strange hum stopped. Everything seemed fine.

The problem is that my friend installed this set in his home and he reported shocks. While testing with a line tester, he found the equipment to be slightly live.

What could be the cause of this problem?

  • 3
    \$\begingroup\$ Your friend needs a visit from an electrician. His electrical outlet(s) are not grounded as he probably thinks they are, giving him a false sense of security. \$\endgroup\$
    – brhans
    Commented Jun 5, 2017 at 17:23
  • \$\begingroup\$ That point seems to be obvious. I will check that with him. \$\endgroup\$
    – user132257
    Commented Jun 5, 2017 at 17:33
  • \$\begingroup\$ What do you mean "slightly live"? \$\endgroup\$ Commented Nov 5, 2021 at 11:20
  • \$\begingroup\$ The neon glow tester that he used wasn't fully bright but it was mildly lit. The problem seems to be their earth connection as they have been using two pin extension boards for a three pin SMPS power supply \$\endgroup\$
    – user132257
    Commented Nov 27, 2021 at 9:33

1 Answer 1


In some homes, their Earth line/wire is not grounded (aka its not actually touching the earth/soil), and it left floating (God knows why). Same thing happened to my company. We are on the 1st floor. One day we checked the Earth line at he basement, and the Earth Wire was floating! The wire was just there, and did not connect to anything.

We tied it to the GND, and then we were grounded. Some equipment worked better after that!


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.