A simple earth leakage indicator circuit discussed here can be used for getting some very useful results regarding current leakages from an appliance body into the earth pin. The idea was requested by Mr. SS kopparthy.
The circuit of the proposed earth leakage indicator is shown in the figure below.
Each such unit may be used for individual appliances having earth pins, or a single circuit may be placed near the MCB for detecting a possible common leakage from all the appliances.The circuit may be understood with the points I have explained below:
Circuit Operation
R2 is positioned as a current sensing resistor which should have a relatively low value so that the actual earthing feature doesn't get obstructed due to its resistance.
T1 here forms a current sensing and a voltage amplifier stage. The detected small voltage across R2 is quickly amplified by T1 and fed to the LED inside an opto coupler.
As long as the leakage is not relatively significant (below 20mA) the LED inside the opto does not respond, however the moment this value exceeds the set limit, the LED inside the opto illuminates switching ON the corresponding built-in transistor, which in turn actuates the red LED connected across its collector and positive lead indicating a possible earth leakage.
The supply for the entire operation is derived through a small trasformerless power supply using C1, D1, C2 as its main components.
The red LED may be replaced with a 12V piezo buzzer for getting an audio indication, or both may be used in parallel for facilitating a dual mode indication.
The value of R2 may be calculated using the following formula:
R = 0.2/I. where I is allowable current leakage through the earthing cable, assuming this to be 20mA we can calculate it as:
R = 0.2/.02 = 10 ohms
Since the collector resistance if T1 is quite high, T1 could get triggered with as low as 0.2 across its base/emitter, that's the reason why 0.2 is selected in the above formula.
The T2 stage is introduced for monitoring the "health" of the earthing connection, as long as it's at par with the neutral, T2 stays switched off since its base remains grounded via the good earthing, however the moment a weak earthing is formed, T2 base gets enough voltage through R5 to trigger itself and the opto which in turn triggers the connected alarm.
The situation of a weak or open earthing is indicated by the red and yellow LEDs together, while the red LED alone indicates an earth leakage.
CAUTION: THE CIRCUIT IS NOT ISOLATED FROM MAINS, ALL PARTS COULD CARRY LETHAL ELECTRIC CURRENT, EXERCISE UTMOST CAUTION WHILE HANDLING UNCOVERED.
Parts List
R1 = 1K ohms
R2 = see text
R3, R4 = 22k
R5 = 56K
R6 = 1M
D1 = 15V 1watt zener diode
C2 = 100uF/25V
T1, T2 = BC547
C1 = 0.47uF/400V
opto = any standard 4-pin type
The above circuit could be improved by adding a few more components to it, as shown below:
In this circuit we have added a rectifier diode D1 (1N4007) for an improved rectification.
T1 has been enhanced with another BC547 transistor T2 wired as Darlington in order to make the earth leakage detection even more sensitive and allow the use of smaller in-line resistance R2 for better "earthing" experience for the appliances.
C2 (0.22uF) ensures that T1/T2 does not get rattled with unwanted electrical disturbances.
Parts List
R1 = 1K
R2 = see text
R3, R4 = 22k
R5 = 56K
R6 = 1M
Z1 = 15V 1watt zener diode
D1, D2 = 1N4007
C0 = 0.47uF/400V
C1 = 100uF/25V
C2 = 0.22uF
T1, T2, T3 = BC547
C1 = 0.47uF/400V
opto = any standard 4-pin type
Test Set-Up for the above circuits:
Earth Leakage Indicator
The above diagram shows the test set-up for the proposed earth leakage indicator circuit.
It's conducted in the following manner:
The circuit powered up using an external 12V AC/dC adapter output, remember do not plug-in the circuit to mains while doing this procedure
In the set-up test 12V AC supply is connected across the earth/appliance points via a 12V bulb.
R5 link is kept disconnected for the time being.
The above implementation should instantly switch ON the red LED indicating a current leakage through R2.
Disconnecting the 12V bulb, the red led must also switch OFF, indicating the stoppage of the leakage condition.
Now reduce the 12V bulb load to some lower value, could be done by including another 12V bulb in series to it.
Even with such lower loads, the red LED should be able to indicate the leakages across R2 confirming the proper working of the circuit.
Now removing the above load should instantly switch off the red LED, assuring a correct working of the circuit.
Restore the circuit to its original condition and now it's ready for the actual installation near your MCB.
The functioning of the yellow LEd can be witnessed after the actual installation and connections are done.
If it starts glowing immediately after the installation would indicate a bad or incorrectly wired earthing line.
Comments
Dear sir, this is my problem :
1)if any appliance leaks in other houses, the current or leakage comes from EARTH TO APPLIANCE BODIES in our home.
2)but however the current passes through r2 but in REVERSE manner viz., earthing pin to appliance body, in this condition , does circuit detect and indicate, sir?
3)Or if the leakage should come from appliance body, then the earthing wire should be connected to appliance body/bodies nomally and r2 up end should be connected to body/bodies and down end to earth I.e., r2 up and low ends are connected together and connected to earth……
I'll try to draw a example schematic of above explanation so that you can understand easily….. thank you very much my dear sir…….
Regards, ss.
Dear sir, bu the way, I didn't get th e point how to connect the circuit to ground and appliance… is it like this…. appliance earth wire—–r2—-into earth. If it is like tthis, then if I want to get common leakage from all appliances, then I hav to cut th appliances common earth wire and connect it to upper end of r2 and lower end to earth….right sir? But what I wanted to tell you is that I am living in a apartment..and its proved that the geyser is leaking voltage into earth…so when ever they switch it on, we get shock from our appliances as their body is also connected to same earth…….. so I think this circuit doesn't suit for my need bcz I cannot cut the earth wire from homes and keep this in middle of home earth wires and main earth……..so if this circuit should help me, it should sense the voltage from eathing pin and give buzzer thats all…, if I'm right…….if I'm not wrong, I think I should eliminate r2 and connect the r1 to earth pin and remove weak earth sensing part of the circuit,…..maybe…..hope you understand my doubt and find a solution for it……thank you very much sir….
Yours
Ss.
Dear SS, the earth leakage current must pass through R2 otherwise it won't detect anything. You must remove the earth main connection from one of the sockets where it enters first near MCB and connect it with the circuit's "earth"…. next connect the "appliance" point of the circuit to the socket point from where the above earthing wire was disconnected.
Dear sir, thank you for your he) p ill wait until you update the article with testing related guidance……and by the way, I bought a new capacitor today(new stock arrived)….because I cannot trust that old capacitor, it is also damaged a bit as you can see….here's the pic of NEW capacitor…https://drive.google.com/file/d/0B_R45ksolHSmb3o0anVfalpfSVU/edit?usp=sharing …..the size of this is very small, but the retailer told its 400v only……please confirm….thak you and regards….
SS, this circuit will not detect your neighbour's appliance leakages, it will only detect your house appliance leakages
And I forgot onething, the geyser that is leaking is not ours, its our home's beside portion's geyser that is leaking and they never change their geyser or coil……such a brainless people, they even dont know that they too get shock, and they never listen to other's words!!!!! Please help me how to modify this circuit and to make it to help me…..thank you very very very very very very very very very very very very very very much sir……
Ss.
Dear sir, you are right, though I eanted to buy a new one according to your advice, I tested it(bcz retailer told its 400v). I connected led as a load after 10k 1watt resistor and 1n4007 diode, 100mf 25v cap, 15v 1w zener……and after wometime the capacitor BLEW….and immediately, I switched off the mains switch…and all this is done under adult supervision and with safety like goggles, fire extinguisher and circuit is at a distance of 5metres from me bcz I connected the cicuit to mains ising 5mtr extension box….now I understand tht i should follow your advice exactly or face the consequences!!!!!!!!!!…now ill buy a capacitor which has volts print on it….and show it to yo u before using……telling thanks, regards, etc.. doesn't suit you bcz your help is more than what those words could mean…. -SS.
Dear SS, I have updated the diagrams appropriately, please check above and follow them accordingly.
I am not sure if it's 400V rated because the codes are not familiar to me, even I could not find them through online sources, better replace it with a properly indicated capacitor, the voltage print is a must.
Dear sir, thank you very much…..here is the link of th e capacitor….https://drive.google.com/file/d/0B_R45ksolHSmNXJyQzFZcl9nVVU/edit?usp=sharing Also please tell me if I should use DIL(dual-in-line)for soldering the opto sir, or if I should directly solder the opto on strip board. ?..sir, this is the first time im usng a opto…that's why I am getting this doubt…….and here is the pic of new capacitor that I bought today if you tell me which to use, ill proceed……thank you very much….and I assure…."no more doubts and disturbance"….once you reply, I'll be back soon with Pics of circuit…….
Yours,
Ss….with best regards…
Dear Ss, you can include a fuse, but MOV may not be required because the zener diode would take care of the surges. use a 1amp fuse
thank you very much for your invaluable help sir……….
Dear sir, can i use a fuse and mov to protect the circuit from spikes and high current? if i could include a fuse and MOV please help me by suggesting a MOV and the fuse rating….
thank you very much sir……….
regards
ss.
Dear SS, the capacitor is OK, can be used here.
Solder the opto directly on the general purpose board just as we solder an IC or any electronic component, make sure you do not short the pins while soldering.
do it on table first, test it with 12V DC from a 12V adapter.
I'll try to post a diagram of the test set up soon may be.
Dear sir,…first of all very sorry for disturbing you again and again, i wanted to ask you something…..I got the 4n35 opto…and It has six pins, can you help me out and tell me which pins I hav 2 use sir….? And also please see this pic https://docs.google.com/file/d/0B_R45ksolHSmNXJyQzFZcl9nVVU/edit?usp=docslist_api
This is a component which I found in a desktop's cpu power supply 4 years ago….I dont know whether it is a capacitor or not…..but I think its a capacitor thst is specified above…..can you please tell me ig I can use it……
Best regards,
Ss.
Dear SS,
the image is not opening, you'll need to change the sharing option to "public" for enabling that.
for the opto-coupler you can refer the following image:
http://www.wvshare.com/img/pinout/4N25-28_35-37_l.jpg
Dear sir, if I want to connect the unit in common to all appliances, near MCB, should I eliminate r1 and r2 and connect the base of T1 to earth…?…..thank you very much sir…..
dera SS, you'll need to first check and confirm the circuit on table, if everything goes right only then you should go for the final install…
dear sir, i thank you very much for you advice…..i know its quite risky job to open MCB….and i never do it whatsoever the circumstance be…so i asked my parents and they informed an experienced electrician(yesterday) and he would do the job…only soldering would be done by me….
i thank you once again for your valuable advice….
Dear SS, R1, R2 are the heart of the circuit, they are compulsory.
connect the "earth" to main earth of the board and "appliances" to the earth line of the home wiring.
please note: this circuit is not easy and will require an expert's assistance and is also highly risky, not recommended for hobbyists under 18.
Dear sir, thank you for all your help……and a final help is needed regarding the 15v 1 watt zener, which is unavailable in my area….so I wanted to ask you if I could use a 18v or 12v zener in the place of 15v zener(I will use 7815 if I could, pls tell me)…..also the optocoupler is unavailable(today some shops are closed but tomorow I'll check rest of the shops….)but in case they're not available, can you guide me how to make a homemade opto…, if possible…..I cannotysay any thing like thanks….because there is no word in this world with which one could thank your hardest of the hard works…..your hard work really returns you a lot in future……I dont even know how to express my thankfulness…you're great man,….perhaps a man born to help…..and an embodiment for millions in this world!!…..what else can I say for your help…..??
yours,
ss.
Thanks you SS, it's my pleasure!
Opto coupler are easily available in electronic spare parts market, you could use any 4 pin type such as 4n35, the retailer will suggest you if there's an equivalent.
i wish you all the best!
Dear Swagatam, while i have not yet build this. But on my appliance The Freezer and CPU Computer, got sum of about 100v at Ac voltmeter, may T1 handle it ?.
There is no rectifier diode, is it not dangerous for c2 and D1 while negative current would flow at 0.6V on D1 forward bias.
Kindly, help me understanding for these. Thank you very much.
Best Regards. Gani in Batam.
Dear Gani,
The transistor is no connection with the load, it's positioned only for sensing the volatge across R2.
The zener diode passes the psotive 12V and grounds all that's negative so it behaves like a rectifier diode also, but you may include a 1N4007 diode if you feel so.
the diode should be in between the circuit positive line and C1, and the zener across the junction of C1/rectifier diode and ground