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Need guidance for earth failure indication

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Rajaneesh

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Hi All ,

Can anyone give me an idea to build a simple circuit for Earth failure indication?

If earth connection fails , the indicator should light... I have some view which is cited down.

Between Earth and neutral , there will some voltage ( 3 to 10V ). By using a comparator circuit , we can switch a transistor which in turn light the indicator(LED) .

Is there any other simple way to do this? I mean With out using any electronic circuit .............

Your valuable points are welcome...
 
Rajaneesh said:
Hi All ,

Can anyone give me an idea to build a simple circuit for Earth failure indication?

If earth connection fails , the indicator should light... I have some view which is cited down.

Between Earth and neutral , there will some voltage ( 3 to 10V ). By using a comparator circuit , we can switch a transistor which in turn light the indicator(LED) .

Is there any other simple way to do this? I mean With out using any electronic circuit .............

Your valuable points are welcome...

Hi,

The usual way to check for EARTH line continuity is to connect a mains voltage rated lamp, say, 60Watt between LINE and EARTH.

If the EARTH is connected the lamp will light at full brilliance.[unless the lamp is 'blown' [ie: open circuit]
A 'high' resistance to EARTH will cause the lamp to dim, with no EARTH connection the lamp will not light.

You cannot rely on the small/variable voltage between EARTH and NEUTRAL.
 
You can invert the above by connecting a mains rated lamp or voltmeter between the earth and an independant earth well away (10 to 20 metres) from the existing earth and waterpipes.

If the earth fails, a voltage will develop between the earth and the independant earth only under fault conditions of the appliances connected.

Under normal conditions there should be no current flow in the earth wire for non MEN installations.
I take it that in India the Neutral and Earth are separated from each other.
 
Re Earth fault indication

HI Eric n Rodalco .

Thanks for your points. But i have an equipment in which P.N.E are there. If earth fails , i need to glow the indicator ( Neon or any low voltage type bulbs) . Hoping to hear from you...

Thanks




ericgibbs said:
Hi,

The usual way to check for EARTH line continuity is to connect a mains voltage rated lamp, say, 60Watt between LINE and EARTH.

If the EARTH is connected the lamp will light at full brilliance.[unless the lamp is 'blown' [ie: open circuit]
A 'high' resistance to EARTH will cause the lamp to dim, with no EARTH connection the lamp will not light.

You cannot rely on the small/variable voltage between EARTH and NEUTRAL.
 
A neon needs at least 60 volts to strike.
An additional series resistor needs to be added to limit the current.
For 220 Volts operation a 220 k.ohms ½ Watt may be used in series.

A high efficiency LED can be used also. I have used 5000 MCAD LED's at mains voltages for indicator lamps.
I set the current at about 3 mA which is ample for those led's.
Use 2 x 33 k.ohms 1 Watt R's in series with the led. a 1 N914 in anti parrallel with led and a 1N4007 forward biased in series with led.

Q. Why would you have problems with your earth ??
 
Rajaneesh said:
HI Eric n Rodalco .

Thanks for your points. But i have an equipment in which P.N.E are there. If earth fails , i need to glow the indicator ( Neon or any low voltage type bulbs) . Hoping to hear from you...

Thanks

Hi,
This circuit is more complex than a simple lamp.
I prefer Fig #1 as its isolated, Fig #2 is NOT isolated.

Using either circuit will enable you to switch ON any indicator/alarm you choose, as its uses an isolated relay contact.

If you are interested, let me know your local mains voltage and frequency.

Eric
 
Last edited:
hi,
This is the most basic circuit that I can think of at this time.
 
Last edited:
Re Earth fault indication

Hi Eric ,

Your idea sounds good. Thank you so much for your dedicated response. Here the mains voltage will be 220 to 235V at the max. Wating to hear from you..

Thanks.

ericgibbs said:
Hi,
This circuit is more complex than a simple lamp.
I prefer Fig #1 as its isolated, Fig #2 is NOT isolated.

Using either circuit will enable you to switch ON any indicator/alarm you choose, as its uses an isolated relay contact.

If you are interested, let me know your local mains voltage and frequency.

Eric
 
Re

Hi Rodalco

Thank you for your timely response.



RODALCO said:
A neon needs at least 60 volts to strike.
An additional series resistor needs to be added to limit the current.
For 220 Volts operation a 220 k.ohms ½ Watt may be used in series.

A high efficiency LED can be used also. I have used 5000 MCAD LED's at mains voltages for indicator lamps.
I set the current at about 3 mA which is ample for those led's.
Use 2 x 33 k.ohms 1 Watt R's in series with the led. a 1 N914 in anti parrallel with led and a 1N4007 forward biased in series with led.

Q. Why would you have problems with your earth ??
 
Rajaneesh said:
Hi Eric ,

Your idea sounds good. Thank you so much for your dedicated response. Here the mains voltage will be 220 to 235V at the max. Wating to hear from you..

Thanks.

Hi,
What is your mains frequency 50 or 60Hz?

Which circuit Fig# do want to use? 1,2, 3 or 4
 
I would just turn the circuit off at the ciruit breaker and measure the resistance between the earth and neutral connections. It should be very low, less than 1:eek:hm:, if it's greater than about 2:eek:hm: then I would think that something could be wrong.
 
Circuit designer should keep in mind that the metal frame/case of the appliance is connected to earth, inside the confine of the appliance. Any circuit which detects the integrity of earth connection for breaks in the cable must not energise the metal case/frame so that it carries dangerous voltage, with respect to common ground. When someone touches the case, this is worse than a broken earth connection. A few mA is all is that needed to kill.
 
Hero999 said:
I would just turn the circuit off at the ciruit breaker and measure the resistance between the earth and neutral connections. It should be very low, less than 1:eek:hm:, if it's greater than about 2:eek:hm: then I would think that something could be wrong.

hi hero,
He's looking for a dynamic system working in real time 24/7.

Why I have no idea!:rolleyes:

Eric
 
eblc1388 said:
Circuit designer should keep in mind that the metal frame/case of the appliance is connected to earth, inside the confine of the appliance. Any circuit which detects the integrity of earth connection for breaks in the cable must not energise the metal case/frame so that it carries dangerous voltage, with respect to common ground. When someone touches the case, this is worse than a broken earth connection. A few mA is all is that needed to kill.

If he decides which circuit he going to use,
I will recommend that it will be enclosed in a plastic box, with no metal external connections to the user/observer.

As the circuit shows NO connection to Earth to the 'unknown' enclosure, I cannot see how he would get a shock anyway.

My domestic earthing system is connected to the metal rising cold water supply as well as the armoured cable screen.

If I ever suspected that the Earth could be lost I would bury a long copper rod with a thick cable attached to act as a secondary earth
 
Re Earth fault indication

Hi Eric,

The Mains frequency is 50Hz. I prefer your 3rd circuit,which sounds the best. Can you please explain the current wave path function of diode network D1 - D4?

In case if the line and Neutral interchage, what will happen? ( Juz for my info please)

Thanks in advance.




ericgibbs said:
Hi,
What is your mains frequency 50 or 60Hz?

Which circuit Fig# do want to use? 1,2, 3 or 4
 
hi,
Fig #3.

D3 diode, is to allow only the positive half cycle of the mains supply [LINE] to pass current thru the LED.

D2 diode, is to ensure that a reverse voltage [>0.7v] cannot be applied to the LED.

D1 diode, conducts on the postive half cycle of the mains supply [LINE], when the EARTH connection is present.
This positive half cycle D1 conduction shorts out the D3 diode and LED, so the LED is NOT lit when the EARTH is present.

When the LINE voltage has a negative half cycle, [the EARTH/NEUTRAL will be positive with respect to the LINE],
then D1 diode blocks any current flow thru diode D3 and the LED.

In the event of a total loss of the EARTH connection, D1 will no longer conduct and the postive half cycle of the
mains voltage [LINE] will be drive current thru diode D3 and the LED.
To increase the apparent brightness of the LED a 16uF 16Vwkg capacitor could be connected in parallel with the LED.

As you have measured only a 2v to 3v differential between the EARTH and NEUTRAL this circuit will be OK.
For higher differential voltages I would add a suitable Zener diode in series with D3.

The circuit is designed to detect the total loss of the EARTH connection and is not designed for detecting EARTH/NEUTRAL connection reversals

The stated specification and value of the C1 capacitor are very important.

Capacitive reactance[ohms] = 1/(2 * pi * f * C)

So for a nominal 20mA half cycle, current thru C1 with a mains suppy of 250Vac at 50Hz, the formula reduces to....

C1= Ima/(V * 2 * pi * f ).............. = 0.02/( 250 * 6.28 * 50) = 0.25uF [ pref value 0.22uF] at 500Vac rating Polypropolyne.

For reference, a capacitor value of 0.47uF would give a nominal half cycle current of 40mA


Important:
this circuit is NOT mains isolated and should be enclosed in a non conductive enclosure which prevents
accidental contact with the circuit/wiring.

If you get a 'Wall wart' psu style plug assembly enclosure you could build the circuit within that enclosure.

Can you say why you are having/expecting problems with EARTH connections and possible EARTH/NEUTRAL reversals???
 
Last edited:
Re to Eric

Hi Eric,

Thanks for the elaborated reply.

The 47 ohm line resistance, how do you arrive? Is it based on LED application current?

---------------------------------------------------------------------
To Eric qstn...

My equipment generates static electricity during operation, and its gives heavy weight kick if the earth fails. So i plan to have an indicator for the same.

And regarding the PH- NTRL reversal, it's very common in india. No stringent rules for generation, boosting , refining , transmission , step down process , and distribution. Second thing distribution lines are loaded heavily some time which lead to heavy dips and flectuations.
----------------------------------------------------------------------

It seems you have a rock solid knowledge in this profession. May i know your profile please, if you dont mind?


Thanks


ericgibbs said:
hi,
Fig #3.

D3 diode, is to allow only the positive half cycle of the mains supply [LINE] to pass current thru the LED.

D2 diode, is to ensure that a reverse voltage [>0.7v] cannot be applied to the LED.

D1 diode, conducts on the postive half cycle of the mains supply [LINE], when the EARTH connection is present.
This positive half cycle D1 conduction shorts out the D3 diode and LED, so the LED is NOT lit when the EARTH is present.

When the LINE voltage has a negative half cycle, [the EARTH/NEUTRAL will be positive with respect to the LINE],
then D1 diode blocks any current flow thru diode D3 and the LED.

In the event of a total loss of the EARTH connection, D1 will no longer conduct and the postive half cycle of the
mains voltage [LINE] will be drive current thru diode D3 and the LED.
To increase the apparent brightness of the LED a 16uF 16Vwkg capacitor could be connected in parallel with the LED.

As you have measured only a 2v to 3v differential between the EARTH and NEUTRAL this circuit will be OK.
For higher differential voltages I would add a suitable Zener diode in series with D3.

The circuit is designed to detect the total loss of the EARTH connection and is not designed for detecting EARTH/NEUTRAL connection reversals

The stated specification and value of the C1 capacitor are very important.

Capacitive reactance[ohms] = 1/(2 * pi * f * C)

So for a nominal 20mA half cycle, current thru C1 with a mains suppy of 250Vac at 50Hz, the formula reduces to....

C1= Ima/(V * 2 * pi * f ).............. = 0.02/( 250 * 6.28 * 50) = 0.25uF [ pref value 0.22uF] at 500Vac rating Polypropolyne.

For reference, a capacitor value of 0.47uF would give a nominal half cycle current of 40mA


Important:
this circuit is NOT mains isolated and should be enclosed in a non conductive enclosure which prevents
accidental contact with the circuit/wiring.

If you get a 'Wall wart' psu style plug assembly enclosure you could build the circuit within that enclosure.

Can you say why you are having/expecting problems with EARTH connections and possible EARTH/NEUTRAL reversals???
 
hi,
The 47R is just a protection measure for the circuit against inrush currents and voltage spikes.

You have a PM.

Eric
 
RE

Hi Eric,

I tried the 3rd circuit . The same is not working as we discussed. The voltage between Earth & Phase is 235V and Earth & Neutral is 0.65V . I removed the earth and checked, the LED dint lit. Voltage across the LED is around 230V. I have used 0.22mfd / 500V poly cap. Is the correct voltage reading of the points? What could be the fault?

Thanks


ericgibbs said:
hi,
The 47R is just a protection measure for the circuit against inrush currents and voltage spikes.

You have a PM.

Eric
 
Rajaneesh said:
Hi Eric,

I tried the 3rd circuit . The same is not working as we discussed. The voltage between Earth & Phase is 235V and Earth & Neutral is 0.65V . I removed the earth and checked, the LED dint lit. Voltage across the LED is around 230V. I have used 0.22mfd / 500V poly cap. Is the correct voltage reading of the points? What could be the fault?

Thanks

Hi Rajaneesh,
I will post a circuit with the voltages you should get at different points on the circuit.
When you measured the 230V across the LED, where was the meter connected as reference?

Eric
 
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