Grounded Neutral condition detection.

Thread Starter

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.
 

LadySpark

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.
Screenshot_2024-03-26_09-27-51.jpg
 

Reloadron

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.
Earth Grounding Service Entry.png

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

Ron
 

Reloadron

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.
 

Reloadron

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.
 
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