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

Sensacell

Joined Jun 19, 2012
2,722
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!
 

Thread Starter

Nanda Kumar 1

Joined Aug 25, 2016
40
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!
I want for an automated detection circuit.
 

crutschow

Joined Mar 14, 2008
26,408
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.
 

Thread Starter

Nanda Kumar 1

Joined Aug 25, 2016
40
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.
thank you for your reply @crutschow . But i want circuit where if line and neutral gets reversed it will break the circuit.
 

BillB3857

Joined Feb 28, 2009
2,542
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.
 

BillB3857

Joined Feb 28, 2009
2,542
@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
 

Tonyr1084

Joined Sep 24, 2015
5,707
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.
 

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