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Leakage Current in the circuit Ground Plane

Aakash Dey
Intellectual 590 points

When I have connected the AC Power supply, I get a little shock when I touched the GND of the circuit. When checked by connecting a tester to the GND of the circuit, the tester indicates a potential in the GND plane (see Image attached). I can't able to measure that potential. But, what could be the reason of this potential? In it AC or DC?

While searching, I found that TI has a leakage current measuring board (www.ti.com/.../tidu873a.pdf. So, Can I use this board to measure this GND current in my circuit?

  • 0
    TI__Mastermind 30810 points

    Hi,

    There is not enough information to tell with any certainty the possible reasons for the cause and nature of the ground potential. However from the look of your tester, it appears your board ground is at some AC potential. You probably should also look at the schematic, and see how the board ground is defined.

    Regarding the second question, the reference design can be used to measure insolation. It probably can be useful if you identify the leakage path. But I would understand the nature of the issue first.

    Regards, Guang

  • 0 in reply to Guang Zhou
    Intellectual 590 points

    Dear Guang,

    Thanks for your reply.

    Earlier I have practically tested but can't able to find the reason. So, I have attached the AC Power Part of the Schematic. Please suggest me if there is any wrong with the schematic.

    Also, after measuring the path, How can I measure this leakage current?

    What should I change in the schematic to avoid this leakage? If I connect the circuit Ground to EARTH though a metal plate ( below image), would it be enough to avoid this leakage?

    Thanks.

  • 0 in reply to Aakash Dey
    TI__Mastermind 30810 points

    Hi Aakash,

    Based on the schematic, the rectifier circuit should work. If your power source, ie utility electric, is wired up to US code, there should be no electric shock problem.

    For your circuit, please don’t connect the circuit ground to Earth ground with a metal plate. Doing so directly violates the code, and is potentially dangerous. The correct thing to do, for your own safety, is to find the main breaker panel of the outlet you’re using and make sure Neutral is grounded there. Alternatively find another power source that is properly wired in accordance with code. You should request service from a licensed electrician in investigating/implementing such panel work.

    Also just another advice - proper PPE and lab equipment are required in working directly with utility electric. Please check with your local regulations and make sure you're in compliance. 

    I highly doubt you have a leakage problem that is causing the issue. But I’ll answer the remaining question anyway – the ref design you found measures isolation through measuring leakage. Since they are related, I’m fairly certain knowing one should enable us to know the other.

    Regards, Guang

  • 0 in reply to Guang Zhou
    Intellectual 590 points

    Hi Guang,

    "The correct thing to do, for your own safety, is to find the main breaker panel of the outlet you’re using and make sure Neutral is grounded there."

    Current I am using the below configuration to supply the power to my circuit.

    That's why I want to connect my circuit GND to Earth wire through a metal plate like many electrical/electronics equipment's. By you are saying that it may dangerous. How? kindly please explain as this connections  I have seen in many electrical/electronics equipment's.

    Also, if you are telling to grounded the Neutral line, I can directly connect the Earth terminal of the Socket to the Neutral terminal of the socket side only. Is it fine? Will it be able to bypass the leakage current in my circuit GND to the earth?

    Thanks.

  • 0 in reply to Aakash Dey
    TI__Mastermind 30810 points

    Hi Aakash,

    Please consider my opinions as mere good-will suggestions, because this topic is outside the scope of this forum. You should seek advice from a licensed electrician or a registered PE in this matter. However I’ll continue to offer my 1 cent, please consult with real experts for actual solutions.

    When you connect neutral and earth (equipment) ground together, you’re simply transferring the shock risk to the equipment ground, which is normally tied to the enclosure if it is made of metal. Anyone comes in contact with the enclosure is now exposed to shock risk.

    Like I said previously, connecting equipment ground and neutral at the equipment is against NEC code due to above reason. If the branch circuit is GFCI protected, it will trip the breaker.

    Regards, Guang