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Shock from arduino

Discussion in 'General Electronics Discussion' started by Karthik rajagopal, Aug 18, 2019.

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  1. Karthik rajagopal

    Karthik rajagopal

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    May 9, 2016
    Hi all,
    I was trying out some projects with arduino . I was curious to know the changes in the readings that an analog input will show when it is left free than when touched (through a wire) . So I tried it out and when I touched it nothing happened . But when I touched the wall while holding the input pin ,I felt a electric shock which wasn't too high but was enough to make my hand fell the discomfort for few minutes. I didn't know how I felt that . I was programming my arduino in my PC .So I thought that it must be due to the smps power supply which usually happens when we touch a smps supply. My question is how did I fell that shock in an input pin? In my case it was A0 pin on the arduino which is the analog input.
    Please help me understand what really happened here .
    Thanks in advance .
     
  2. Minder

    Minder

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    Apr 24, 2015
    Your Arduino project must have live chassis WRT the earth GND.
    You normally will not get one from a PC as the SMPS in all the ones I have ever serviced has the power common connected to earth GND.
    It is most likely that you do not have a proper earth conductor.
    M.
     
  3. Karthik rajagopal

    Karthik rajagopal

    238
    9
    May 9, 2016
    Thanks for the reply. As per your reply I think I must replace my smps in my computer bcoz I have been experiencing the shock even if I connect a normal USB cable with exposed wire . If my smps is replaced, will that solve my problem (shock from my arduino )?
    Thanks
     
  4. Minder

    Minder

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    Apr 24, 2015
    If your Arduino is fed from the PC PS and is properly grounded you should not receive any shock.
    If no ground in the SMPS itself, it is usually bonded to the case by the MB screws.
    I would check the validity of your earth conductor from the outlet etc.
    M.
     
  5. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    [​IMG]

    AC power distribution wiring in India can be problematical. Proper grounding often does not exist. It would be a good idea to hire a licensed electrician to check, and it necessary repair, the AC wiring you are using.
     
  6. Bluejets

    Bluejets

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    Oct 5, 2014
    .............and get yourself (at the least) a plug in safety switch.
     

    Attached Files:

  7. Karthik rajagopal

    Karthik rajagopal

    238
    9
    May 9, 2016
    Sure . I will do it. As you mentioned, grounding has been a problem in some areas . Thanks for the reply .
     
  8. Karthik rajagopal

    Karthik rajagopal

    238
    9
    May 9, 2016
    Thanks for the reply .Is it like an extension panel? Does that include any tripping mechanism ?
     
  9. Karthik rajagopal

    Karthik rajagopal

    238
    9
    May 9, 2016
    Must call a technician to look into this earthing problem in my smps .My computer's smps was recently changed and I doubt the service man would have replaced that with a low cost one or must have forgot the ground connection .
     
  10. Bluejets

    Bluejets

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    Oct 5, 2014
    Yes, obviously otherwise what would be the point of using it.
     
  11. Karthik rajagopal

    Karthik rajagopal

    238
    9
    May 9, 2016
    Then I will purchase that right away. Will definitely be useful here .Thanks
     
  12. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    @Bluejets: Will those "safety switches" still work if they are plugged into receptacles that do not have a good earth ground? I know nothing, zip, about such things, but imagined they were somehow a combination of circuit-breaker and ground-fault circuit interrupter or GFCI.

    A circuit-breaker works just fine without an earth-ground, unless it is a GFCI circuit breaker, so maybe your "safety switches" will too. Do you have a link to a datasheet for one of those puppies? Perhaps a printed description of how they are intended to be used? The closest thing I (apparently) have seen here in the States is a contraption that is an integral part of a removable window air conditioner. It looks like a GFCI with TEST and RESET buttons and requires an earth ground to operate properly. This earth ground is separate from the bonded Neutral, which is connected to a local purpose-driven earth ground, or to a cold-water metal plumbing pipe, located near the distribution panel. I have also noticed such things attached to hand-held blow-dryers of the type used for drying hair after bathing.
     
  13. Karthik rajagopal

    Karthik rajagopal

    238
    9
    May 9, 2016
    I must look for the products available here in my country. 99% I am sure that it is not a grounding problem. I will check my smps connection. That must be the culprit .
     
  14. Bluejets

    Bluejets

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    Oct 5, 2014
    Hi Hop,
    If they are core balance relay driven, (which most I have seen are) then yes.

    The A and N conductors are taken through a toroid core and if not balanced ( usually within 30mA) as in the case of any current flow to earth then the unit will trip.
    I think even in most "crazy wiring" countries there will be supply referenced to earth on the supply neutral somewhere.
    Did a quick Google for a schematic of operation.

    https://updates.clipsal.com/ClipsalOnline/Files/Brochures/G0000110.pdf

    https://updates.clipsal.com/ClipsalOnline/Files/Brochures/W0000573.pdf
     

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    • RCD.jpg
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    Last edited: Aug 20, 2019
    hevans1944 and Karthik rajagopal like this.
  15. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Thank you! It looks like one of these will "protect" the end-user from electrical shocks that result from no less than either 10 mA or 30 mA (depends on model) of unbalanced current between the "active" and the "neutral" AC power lines. This will be true whether either the "active" or the "neutral" (or both) is/are referenced to earth ground somewhere.

    Since apparently @Karthik rajagopal is getting shocked by placing his delicate body between some sort of earth ground and a terminal on his equipment (an Arduino input port ?!), one of the devices you referenced should prevent that if the unbalanced current exceeds the trip threshold. Nice that it is re-settable after tripping too.

    Not related to what you posted, I have unfortunately discovered that many GFCI receptacles sold in the United States have a limited number of trip cycles (including so-called self-test) before they open their protected circuit one last time. I have had to replace two of these poorly engineered GFCI receptacles in our "new" house in Florida that we purchased in 2016 from the original owners, who custom-built the house in 2007. The receptacles are located in our kitchen, at the rear of the counter tops, and consisted of one GFCI receptacle properly "daisy chained" to protect three more receptacles. I did the same thing when I remodeled my kitchen in Dayton, Ohio several years ago, but I didn't discover the diminished life-time until one of them failed after just a few years of in-service use. These were not el-cheapo receptacles either: their cost was upwards of twenty bux each IIRC, which was the incentive to use just one to protect several nearby receptacles.
     
  16. Minder

    Minder

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    Apr 24, 2015
    If you are getting a shock from the 0v conductor or frame of the PC, then it definitely points to no earth connection.
    Obviously the PC should be connected to a 3 pin outlet to obtain the ground connection.
    To check the GND connection itself on the SMPS, do a resistance check from one of the 0v (black) conductors to the case itself.
    Or even measure resistance from one of the USB port common to the frame of the PC. This would be one of the edge pins of the USB.
    Also confirm the continuity of the PC frame to the ground pin on the plug end of the power cord.
    The last scenario would be the earth ground is non-existent on the outlet.
    M.
     
  17. Bluejets

    Bluejets

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    Oct 5, 2014
    If (both) then there would be a dead short on A and N.
     
  18. Karthik rajagopal

    Karthik rajagopal

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    9
    May 9, 2016
    Sure. I will do it and update you . If not will check the grounding of my outlet .
     
    Minder likes this.
  19. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    My interpretation of "referenced to earth ground" does not mean "connected to earth ground." I am using "referenced" in this context to mean "measured with respect to." Please accept my apology for any confusion my interpretation may have caused.

    Here in the USA, typical house wiring is distributed from a center-tapped transformer, providing 120 VAC from either end of its secondary with respect to the center-tap, the latter being bonded to a nearby earth ground and called the "neutral" terminal. Thus, in my interpretation, either and both of the "live" secondary terminals of the transformer, as well as its neutral terminal, are all referenced to earth ground. The voltage between the two "live" terminals is 240 VAC and this voltage is NOT referenced or measured with respect to earth ground.

    I realize that in other countries 240 VAC, measured with respect to earth ground, is a normal distribution usually labeled "A" (the live wire) and "N" (the neutral wire). Other than that, I have no idea how residential electrical power is distributed outside the USA, or whether it is customary or required that the "N" wire be connected to an earth ground. However, it seems like a good idea to me that the neutral wire be connected to earth ground...
     
  20. Minder

    Minder

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    Apr 24, 2015
    Most jurisdictions earth ground the neutral, UK, Australia etc use a 3phase transformer for distribution with every so many residences on one 230v phase, and the star point neutral, which is connected to earth at the transformer secondary.
    At one time it was mandatory to measure ground resistance from the neutral conductor fed to the residence and the earth ground back to the transformer by means of a low resistance Megger measurement.
    Which had to conform to a limited maximum value.
    M.
     
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