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Can someone suggest me circuit to detect the earth to neutral voltage. I would like to trip relay coil using microcontroller if earth to neutral voltage exceeds 3v.

There are device RCB and RCBO which serve for over current protection in these case. If i would like to achieve using PIC or arduino microcontroller how can be done. Please let me know simple circuit or application to get started.

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  • \$\begingroup\$ Why do you want to use a microcontroller? Is it DC or AC voltage detection? RMS or peak? Ever heard of a comparator? \$\endgroup\$ – Andy aka May 11 '18 at 15:29
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    \$\begingroup\$ Whatever you do, don't forget to consider that you can't assume neutral is near earth potential. Isolate your measurement from your system and make sure there's protection circuitry. \$\endgroup\$ – Hearth May 11 '18 at 15:31
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    \$\begingroup\$ @Andyaka nah it's all about DSP these days, he needs an FPGA in there (/s) \$\endgroup\$ – BeB00 May 11 '18 at 15:47
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Firstly make sure you understand exactly what you are trying to sense and why. This Megger document may help you.

Earth and Neutral would normally be bonded at the mains distribution box (power entry) on a building. At this point there obviously should never be a potential difference between Neutral and Earth wires.
Further into the building the N-E potential WILL vary because Neutral carries a current for all loads, and Earth does not.
It's common practice to test the N-E voltage in hospitals, where grounding a patient could be deadly. For this reason medical equipment AC wiring is locally bonded to reduce risk.

Your idea to produce a monitor that triggers a relay trip coil may not be a great idea, unless the unit is separately battery powered (a poor idea in general).
You need to write some specs for what you want to do.

Ask yourself some questions about your functionality:

  1. What are you protecting against?
  2. Is this transient or permanent protection?
  3. What values represent a trip point? (3V is already a dangerous difference if humans are involved)
  4. How will the system be reset after a detection/fault?
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  • \$\begingroup\$ I would like to detect this 3V. Yes its to indicate human being its being danger ,thats reason i wanted to use buzzer for indication purpose, its permanent protection, Like wise in RCD where if phase is balance relay will not trip , if phase unbalance relay will trip. In this case if potential difference is 3v or more trip the relay( Basic Idea) . so is there way can be done through electronic ti.com/lit/an/sboa199/sboa199.pdf \$\endgroup\$ – user50949 May 12 '18 at 1:12
  • \$\begingroup\$ You need power to trip the relay. That's why the earth leakage detectors use current control. You can't guarantee you have any power to trip the relay unless you can draw power from the N-E voltage source. \$\endgroup\$ – Jack Creasey May 12 '18 at 2:42
  • \$\begingroup\$ Is there any way to detect it?? is there any isolated sensor available?? RCB & RCBO are more protective , if any Ic detect like mentioned in my previous comment \$\endgroup\$ – user50949 May 13 '18 at 2:30
  • \$\begingroup\$ what would be difference between ground fault and neutral fault .why cant use GFCI?? weather these relay reliable for sort these kind of issue> \$\endgroup\$ – user50949 May 16 '18 at 7:11

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