Grounded Neutral condition detection.

moonlystar1111

Joined Feb 1, 2024
65
I was trying to simulate a circuit where it can detect grounded neutral conditions in the household. I need to have a current transformer which can detect the current differential ans sends a signal to op amp which can further amplify it/convert to voltage. How can i do this.

crutschow

Joined Mar 14, 2008
34,680
Just use a current-transformer on the ground wire to earth ground in the electrical box.
Any current detected would indicate a short between ground and neutral in the house.

Joined Feb 7, 2024
173
I was trying to simulate a circuit where it can detect grounded neutral conditions in the household. I need to have a current transformer which can detect the current differential ans sends a signal to op amp which can further amplify it/convert to voltage. How can i do this.
I really don't see the use for the application, Because you have to deliberately put a load across line to earth to detect if the earth wire is connected to common which anything more than a simple neon is going to trip a GCFI circuit detecting current flow on earth.
Here is a simple schematic of an outlet tester to show how they test it.

crutschow

Joined Mar 14, 2008
34,680
Here is a simple schematic of an outlet tester
Don't see how that can detect a grounded neutral, which the TS wants to measure(?).

Joined Jan 15, 2015
7,544
I was trying to simulate a circuit where it can detect grounded neutral conditions in the household.
Shouldn't Neutral and Earth Ground be bonded at the service entrance? Here in the US that is how the NEC has things wired.

The National Electrical Code (NEC) states that neutral and ground wires should be connected at the neutral point of a transformer or generator, or at some other "system neutral point". The NEC also states that the neutral and ground wires should be "bonded" together at the main panel, but not anywhere else.

AC receptical testers are actually pretty inexpensive, like these just as a single example.

Ron

sghioto

Joined Dec 31, 2017
5,420
Shouldn't Neutral and Earth Ground be bonded at the service entrance? Here in the US that is how the NEC has things wired.

View attachment 318497

Ron
At my house the neutral and earth ground are connected at the box on the power pole. It's a 4 wire system under the 2017 code in my county.

Joined Jan 15, 2015
7,544
Still not sure they detect what the TS wants (short between neutral and ground).
Yeah but since Neutral and Ground are bonded at point of entry I would expect to see a very low resistance between the two. My residence I read about 0.4 Ohm between Neutral and Ground and if I measure AC Voltage I get about 20 mV AC. So I am also wondering what the thread starter is actually looking to find? Then too, I have no clue where the thread starter is located.

At my house the neutral and earth ground are connected at the box on the power pole. It's a 4 wire system.
Same here, we come in at service entry where Neutral and Ground are bonded in accordance with NEC. 240 VAC split phase, Neutral and Ground.

Ron

crutschow

Joined Mar 14, 2008
34,680
At my house the neutral and earth ground are connected at the box on the power pole. It's a 4 wire system under the 2017 code in my county.
Yeah but since Neutral and Ground are bonded at point of entry I would expect to see a very low resistance between the two.
Okay.
But you all seem to be missing the point that the TS wants to determine if they are also connected together somewhere inside the house, which is a no-no.
Detecting any current in the ground wire would indicate that.

Joined Jan 15, 2015
7,544
But you all seem to be missing the point that the TS wants to determine if they are also connected together somewhere inside the house, which is a no-no.
Detecting any current in the ground wire would indicate that.
Well alrighty then and with that in mind I would go with your initial suggestion using a CT and likely a clamp on flavor to avoid disconnecting anything.

Ron

sghioto

Joined Dec 31, 2017
5,420
I wasn't missing the point but simply implying my house has 4 wires coming into the breaker box not 3 as shown in Ron's photo.

ronsimpson

Joined Oct 7, 2019
3,131
In an old house where there is no ground, it is common to connect ground and Neutral together at the outlets. A tester thinks that is OK. I think an inductance meter will give you an idea how far away the G & N are connected. If they are connected an inch away, we are looking at nH of inductance but if they are connected at the breaker panel the inductance should be much higher.

Joined Jul 18, 2013
28,760
I wasn't missing the point but simply implying my house has 4 wires coming into the breaker box not 3 as shown in Ron's photo.
4 conductors sounds correct ?
120-0(N)-120 & Earth GND?

sghioto

Joined Dec 31, 2017
5,420
Actually L1,L2, N and Ground-Earth

Joined Jan 15, 2015
7,544
Actually L1,L2, N and Ground-Earth
Same as my house.

Actually the service from the pole is 3 wire, L1, L2 and Neutral with ground being a few 8 foot ground rods pounded into mother earth just outside where the service entry is.

Ron

Joined Feb 7, 2024
173
Don't see how that can detect a grounded neutral, which the TS wants to measure(?).
If FG/Earth OK light is on, then common is grounded to earth.

crutschow

Joined Mar 14, 2008
34,680
If FG/Earth OK light is on, then common is grounded to earth.
How can the OK light signify a fault?

Joined Feb 7, 2024
173
How can the OK light signify a fault?
you can't plug in a device to do that because that function would be covered in the GCFI circuit breaker that would trip at the sign of the stray current.

crutschow

Joined Mar 14, 2008
34,680
you can't plug in a device to do that because that function would be covered in the GCFI circuit breaker that would trip at the sign of the stray current.
How does that answer my question?

moonlystar1111

Joined Feb 1, 2024
65
Just use a current-transformer on the ground wire to earth ground in the electrical box.
Any current detected would indicate a short between ground and neutral in the house.
I tried the way you said. Can you have a look at this.

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