How to detect Line (Hot) and Neutral Reversed with the electronic circuit?

Discussion in 'General Electronics Chat' started by Nanda Kumar 1, Sep 2, 2016.

  1. Nanda Kumar 1

    Thread Starter Member

    Aug 25, 2016
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    Hi every one ,
    I want detect the line and neutral reverse with any electronic circuit .Is there any circuit like that ?
     
  2. Sensacell

    Well-Known Member

    Jun 19, 2012
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    For a test? or part of an automated detection circuit?

    Measure between earth ground and the wire in question, the neutral should measure almost zero with respect to ground.
    The hot will measure full line voltage with respect to ground.

    The tricky part is having a ground!
     
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  3. Nanda Kumar 1

    Thread Starter Member

    Aug 25, 2016
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    I want for an automated detection circuit.
     
  4. crutschow

    Expert

    Mar 14, 2008
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    If you have a typical mains circuit with a safety ground then it's a simple matter to measure between the voltage between the hot wire and safety ground, and the neutral and safety ground.
    The first measurement should give the line voltage and the second should give zero volts.
     
  5. Nanda Kumar 1

    Thread Starter Member

    Aug 25, 2016
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    thank you for your reply @crutschow . But i want circuit where if line and neutral gets reversed it will break the circuit.
     
  6. BillB3857

    Senior Member

    Feb 28, 2009
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    They make plug-in testers that will give a visual indication of proper relationships between Hot, Neutral and Safety Ground. Use one of those and monitor the light pattern with photo sensors. The output of the photo sensors could then be used to determine proper connections with a small microprocessor.
     
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  7. #12

    Expert

    Nov 30, 2010
    16,252
    6,751
    This is one way to break the circuit. Connect this circuit and the circuit breaker will break the circuit if the power line and neutral are reversed.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,507
    2,367
    Or a detect relay coil across the neutral and earth conductor.
    Max.
     
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  9. crutschow

    Expert

    Mar 14, 2008
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    If you had said that at the beginning it would have saved a lot of unnecessary posts. :rolleyes:
     
  10. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
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    A simple half wave diode and capacitor with a relay between Neutral and earth will detect if Phase and Neutral is reversed, or just an AC relay.
     
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  11. BillB3857

    Senior Member

    Feb 28, 2009
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  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Looks more expensive than a $25.00 relay, also does it detect line and neutral reversal ?
    Max.
     
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  13. inwo

    Well-Known Member

    Nov 7, 2013
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    Does it need to meet code?
    Connection between neutral and earth is not safe or allowed downside of service equipment.
     
    Nanda Kumar 1 likes this.
  14. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    @Max

    Automatically shuts off the power when any of the conditions below are present. Automatic reset on power restoration.
    Electrical Rating : 120V, 30A
    Surge Suppression(Joules): 2,450
    Cord Gauge: 10/3
    Max Spike Current: 6,500A
    Over/Under Voltage: Yes
    Open Neutral Protection: Yes
    Plug/Receptacle Temperature Trip: 200°F
    Reverse Polarity Protection: Yes
    Miswired Pedestal Indication: Yes
    Open Ground Protection: Yes
    Dangerous Current on Ground Wire Indication: Yes
    Time delay at power up (128 seconds): Yes
    Weather Resistant: Yes
    Lock Hasp Available: Yes
     
  15. Nanda Kumar 1

    Thread Starter Member

    Aug 25, 2016
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    thank you for u r reply @#12 but that cost is more .
     
  16. Nanda Kumar 1

    Thread Starter Member

    Aug 25, 2016
    35
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    thank you u r reply @ Dodgydavei i will try this
     
  17. Nanda Kumar 1

    Thread Starter Member

    Aug 25, 2016
    35
    0
    @crustchow sorry.
     
  18. Nanda Kumar 1

    Thread Starter Member

    Aug 25, 2016
    35
    0
    hi every one i got some circuit while i am searching .
     
  19. Tonyr1084

    Active Member

    Sep 24, 2015
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    Here's how the AC Safety Test Light tester is wired. It's very simple. There are two Neon bulbs under green plastic lenses and there is one under a red plastic lens. The two green lights should be lit and the red light should NOT be lit. If both green lights are lit then the wiring is connected properly. If either of the green lights are NOT lit then it indicates a fault with the wiring, be it an open ground or an open neutral.

    If the RED light is lit it indicates that the Hot and Neutral lines are wired backwards.

    Armed with this understanding it should be very easy to decide just how you want to test a circuit. But for the life of me I can't imagine why anyone would need an automatic detector circuit to be active on the line at all times. When the wiring is installed THAT is when it's tested to make sure it's done right. What's going to change after that? Unless someone physically alters the wiring (or works on the line) nothing should change. And if someone DOES work on it - testing to verify the wiring was done correctly should be performed BEFORE restoring power to the equipment. But if you want an automatic system to monitor it - that's your prerogative.

    ˚J˚
    ˘

    [edit] Looking at my drawing I see I forgot to label the Hot, Neutral and Ground wires. Well, the black is the hot, the grey (symbolic of white) is neutral and green is ground.

    Comment on your video - that's a nice circuit. But where is this circuit going to be installed? Between the wall plug and an extension cord (or device)? What happens if you have no ground to bounce your test against? Without the ground your video circuit will be useless. You MAY get a false sense of security. Just saying - beware of a false sense of security.

    [edit #2] This is assuming you even have a ground. I have three pin outlets throughout my house. A previous owner installed them. But when tested with the light tester it was discovered that the grounds were connected to nothing. So what he did (highly illegal) was to jump the ground pin to the neutral pin. While it's true that ground and neutral all go to the same place, there still can be a danger: One of the outlets in my (what was once an office) was wired with hot and neutral reversed. When I bought the house and was setting up I plugged my computer into this outlet. Keep in mind that the neutral pin was wired to the ground. This made my computer Case Hot. When I plugged the printer into a different outlet it was case ground. When I attempted to plug the printer into the computer that's when I got a tremendous spark and flash of light. Burned a small hole in the back of the computer and destroyed the printer. That could have easily been ME between case hot and ground. I've been there before. Chances are I would have gotten an unpleasant shock. But the potential for a lethal shock was very real.

    If you make sure your home, office or workshop is wired correctly then anything you plug in should be safe. But like I said, if you want to build a circuit - go ahead. Just don't be surprised when it potentially lets you down. No ground = no protection.
     
    Last edited: Sep 3, 2016
  20. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,507
    2,367
    This method with a $20.00 DP relay will cut off the supply when reversed, an extra contact could be added for indicator.
    Max.
     
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