Earth Leaking Heating Element
Moving soon to a smaller apartment with very little storage space we went through a lot of things that we had to get rid of. A rule of thumb was: if we didn’t use the item during the past 12 months it had to go… well, not really, and certainly not for my electronic stuff, but this was the general idea! During this exercise we came across a small table grill. It looked like almost new and we didn’t remember using it a single time during the past three years while we were living in this house. Probably we just forgot about it, having an outdoor barbeque. This is what happens when you have too much storage space… Objects get put aside and forgotten about! This one definitely qualified for the “has to go” category.
Before deciding what to do with this appliance I resolved to test it, thus I inserted the power plug into the wall socket. The grill started heating then, after a few seconds, the house circuit breaker tripped off. Ah, this started to be more interesting! The quiet way the circuit breaker when off, without any spark or other kind of typical “short circuit bang”, let me think that the cause was an earth leakage. I took the appliance up to the workbench for investigation.
The first measurement, using a digital meter between Live and Neutral of the power plug, indicated a resistance of 36 Ohms. This could be considered as normal for a powerful appliance (1600 W / 240 V).
Next step, measuring between Live and Earth, the digital meter was showing inconsistent and unstable readings. It was time to switch to the analog meter. This was one of those situations where the analog meter is much better. An insulation leakage is not a linear load and its value will depends on the current passing through. The analog Ohmmeter supplies more current to the device under test than the digital meter, so we have a better chance to get some reading. The meter displayed a stable value of around 50 kΩ, which indicated an insulation leakage and explained why the circuit breaker tripped off… The insulation resistance must show infinite under any scale of the analog meter. I could also have done an insulation test but the present measurement was enough to highlight the problem.
Let’s remind how this works. A typical household circuit breaker has two functions: a) to interrupt the circuit if the line current goes beyond a certain value and b) to interrupt the circuit if there is an Earth leakage current. Those devices are called Residual Current Circuit Breakers (RCCB) or Earth Leakage Circuit Breaker (ELCB).
The figure below shows one of the RCCB installed in our house. It is labeled 40A and 0.030A. It means that it will trip off if the current is higher than 40A (3 phases) or if the leakage to Earth is higher than 30mA!
In a house or apartment the Neutral is usually connected to the Earth in the entrance switchboard. From there, three separated lines are fed to the power points. Each piece of equipment will be connected to the Phase (Live) and Neutral. The frame or cabinet will be connected to the Earth as seen below. When there is no fault the current flowing from the Phase line will be the same as the current returning through the Neutral. There is no current flowing through the Earth wire.
In case of a fault, part of the Phase current will return through the Earth line instead of the Neutral line. The current returning through the Neutral will no longer be equal to the current flowing from the Phase:
The RCCB measures the current difference between the Phase and Neutral wires. If the difference is more than 30 mA (for most countries) the circuit breaker trips off. The following picture shows the operations principle of a RCCB:
The hart of the device is a magnetic core with three windings. The supply current will create a magnetic flux into the core. The return current (through Neutral wire) will also create a magnetic flux but in the opposite direction. If both currents are equals, those two magnetic fluxes cancel each other. In case of a fault, both fluxes do not fully cancel each other. There will be a residual magnetic flux which will induce a current into the third winding. Remember we are talking about AC, it acts like a transformer. This current energizes the relay to trip off the circuit breaker. Pressing the test button also will create a current imbalance, hence trip off the device.
If the equipment cabinet is not connected to the Earth (broken wire or dodgy installation) the leakage current might flow to the Earth through someone touching the cabinet. A current of around 30 mA (0.030 Amps) is considered potentially sufficient to cause serious harm or a cardiac arrest if it stays for more than a fraction of a second. RCCBs are designed to disconnect the conducting wires fast enough to prevent serious injuries from electric shocks.
Back to our grill, we could suspect that the leakage was inside the heating element. To be sure, let’s open the appliance and disconnect the heating element:
As we can see there is not much in it and it is easy to disconnect the heating element and measure it. As expected the results were the same as measured directly from the power plug. So the heating element is definitely faulty. As the grill is like new but have not been used for more than 3 years I suspected that the problem could have been caused by moisture entering the element. Can it be fixed? I wondered if, by heating the element, we might get rid of the moisture but I wanted to be sure so I did a search on the Internet. Sure enough I found a site where someone restored a coffee machine heating element by heating it on a gas flame. And it worked…
From there, I imagined that I could heat the element by running the grill during a few minutes after temporarily disconnecting the Earth wire (green/yellow in the picture) so the RCCB would not trip off. This can be dangerous and one must be very careful not touching any part of the equipment while doing so. But here we go, for two minutes only:
After a couple of minutes unplug and let it cooling down, reconnect the Earth wire, put everything back together and measure again. Bingo, the Live to Earth resistance went up to around 500 kΩ. This was still not good enough but it was a conclusive improvement. So I decided to give it more time. If it took several years for the moisture to get in we cannot expect it to get out within a few minutes only. So I let it rest for a day (switched off of course)! On the following day the resistance had risen to over 1 MΩ. One more resting day and it barely moved the pointer of the multi-meter on the x10K scale. At this point it was possible to run the grill, Earth connected, without having the RCCB tripping off.
Then I performed an insulation test that shows 1340V. Perfect!
Was the problem fixed and will it return? Time will tell us. It probably depends on how often the ones who will inherit the grill will use it and where the appliance will be stored.
Gerald Musy, Penang- Malaysia
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37 Comments
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Randy
June 20, 2015 at 11:50 pm
nicely thought out and explained, thanks!
Gerald
June 21, 2015 at 9:53 pm
Thanks Randy
Etienne Pourrier
June 23, 2015 at 7:13 am
Highly intellectual. This is the mark of an individual who really knows electronics.
Yogesh Panchal
June 21, 2015 at 1:18 am
Thank you sir for another informative article please keep sharing.
Gerald
June 21, 2015 at 9:39 pm
Thanks Yogesh
Bernie Scott
June 21, 2015 at 2:49 am
Nice article......very nice!!! Keep up the good work.......
Cheers,
Bernie
Gerald
June 21, 2015 at 9:40 pm
Thanks Bernie
Abdul
June 21, 2015 at 8:22 am
This article is very good and informative.
Keep up the good work and keep sharing.
Thank you.
Gerald
June 21, 2015 at 9:41 pm
Thanks Abdul
Mark
June 21, 2015 at 11:07 am
Hey Gerald,
I always appreciate your articles. They are well explained with some theory in the background to help us get the principles involved and a great collection of photos as well.
I will be printing this one out for further reference.
Although I am a licenced 'Tag & Tester', your explanation of how a Earth Leakage Circuit Breaker (ELCB) works was informative and helpful.
Keep up with the instructive articles!
Gerald
June 21, 2015 at 9:44 pm
Thanks Mark for your positive comment. We tend to take those devices (ELCB) for granted and sometimes forget how they work.
Cheers,
Gerald
Ehsan Murad
June 21, 2015 at 12:03 pm
Very good presentation. Easy to understand and digest. One thing confused me. What is significance of getting 1340V in the last picture?Does it mean the insulation will hold upto this amount of voltage?
Thanks
Gerald
June 21, 2015 at 9:51 pm
Thanks Eshan. Yes the 1340 V would be the maximum voltage it will stand. I am not sure how this one instrument works but usually they increase the voltage until a certain amount of current is flowing. This would be a very small current as it is also used to test transistors, diodes etc... It is very useful to find out the reverse voltage of a Zener Diode for example.
Cheers,
Gerald
Gerald
Tito Kanshulu
June 21, 2015 at 6:42 pm
The article is well explained,sir,and it has given me an experience of a life time,more especially on how moisture is removed from the element.
Gerald
June 21, 2015 at 9:52 pm
Thanks Tito
Robert Calk
June 22, 2015 at 3:43 am
Nice job Gerald! Thanks for the article. I need to get myself one of the insulation testers like you have.
Gerald
June 22, 2015 at 1:55 pm
Hi Robert,
Thanks for your comment. Indeed this instrument is a transistor tester. It has a reverse breakdown voltage function that we can use as insulation tester up to 1500V.
I use it time to time to test Zener diodes. As you know the reverse breakdown voltage of a Zener diode is the Zener voltage itself. As they are very hard to read, often too small, I can find out the value this way. It can also be used to test capacitors breakdown voltages. Be careful to discharge the capacitor after this test. I was bitten a few times 🙂
Cheers,
Gerald
Robert Calk
June 23, 2015 at 9:26 am
Hi Gerald,
I was thinking about building my own zener diode tester for high voltage zeners. My Zen 50 only checks them to about 50 volts. It would be cheaper for me to just buy that tester you have. Thanks for bringing it to our attention.
Gerald
June 25, 2015 at 8:37 pm
Hi Robert,
Not sure if this forum is still active. Anyway yes this instrument is very good. If I put an LED on the 200V scale it gives me 2V forward and around 16V reverse. Reminding me that the reverse voltage of an LED is quite low... You can test Zener diodes up to 1500V...
Cheers,
Gerald
Robert Calk
October 10, 2015 at 2:32 am
Hi Gerald,
I'm glad Mr. Yong had this article in the choices on the homepage because I forgot about getting myself the tester. I just went to Ebay and ordered myself one, thanks. I got it for $41.89 US.
Robert Calk
October 14, 2015 at 3:12 pm
I just received the meter earlier today, and I like it. It is a great meter for the price and is very well built. I like that it has a good hard plastic cover that fits over the face to keep it protected. I recommend the meter to everyone. Thanks Gerald.
Ken Hart
June 22, 2015 at 5:32 am
Is the ELCB protector the same as the Ground Fault Circuit Interrupter used in the USA?
A GFCI is either found in the building main circuit breaker panel and looks just like a regular circuit breaker except for having a test button, or it is built into a standard wall outlet and can be used to protect itself and all outlets wired downstream from it. The GFCI senses any electrical connection between the neutral and the earth ground wires.
Gerald
June 22, 2015 at 6:22 pm
Hi Ken, thanks for your feedback. I was not aware of the US GFCI terminology, so I had to do some research on the net. Indeed it looks like it is the same thing as the ELCB. Here is a link:
http://www.nema.org/Products/Documents/NEMA-GFCI-2012-Field-Representative-Presentation.pdf
It also works with a differential current transformer exactly like the ELCB.
Cheers,
Gerald
Waleed Rishmawi
June 22, 2015 at 2:12 pm
very informative. thanks for sharing.
Gerald
June 22, 2015 at 6:23 pm
Thanks Waleed for your support
Humberto
June 23, 2015 at 12:30 am
A good job, explanations are really very didactic and photos very clear. In my country which has a tropical climate we use to put the PCBs to take a sun bath for several hours as a natural method.
Gerald
June 23, 2015 at 3:16 pm
Hi Humberto,
Thanks for your support. Here also in Malaysia where I live we have a tropical climate with humidity over 80%. You are right, the sun bath is often a good solution for some cases. For the heater we needed a bit more temperature 🙂
Cheers,
Gerald
Paul K
June 23, 2015 at 4:18 pm
Great story Gerald.
It reminded me of a fix that my father told me about when he was the service manager at a major appliance manufacturer. Apparently even normal stove and oven elements sometimes do not work properly and end up with a lower than expected resistance.
I am not sure what the symptoms were but I expect that they blew fuses or tripped the breakers since they would draw too much current when turned on. The ELCB would not be a problem since built-in stoves do not pass through an ELCB by default and I believe he was doing this before ELCBs, RCDs and Safety Switches became the normal thing to use.
His solution was a little safer in that you could remove the element causing the trouble and just place it in the oven to heat it externally. After cooling the element would often be restored to a functional state.
I learned a lot from my father. He will be pleased to know that things haven't changed much in the repairing world.
Best wishes to all.
Gerald
June 24, 2015 at 8:37 am
Hi Paul,
Thanks for your comment and support. Your father was right, if we can heat the element externally it is much better and safer. Many old tricks are still valid in every domain. Greetings to your father.
Cheers,
Gerald
Chris
June 26, 2015 at 3:32 am
Hi!
I really enjoyed to read your article and you don I nice description too.
Thanks for sharing.
junfred
January 31, 2017 at 10:58 am
hi, thanks for keep sharing your articles, this help a lot for technical and none technical people ,keep up the good work and more power to you
AC
March 11, 2017 at 7:25 pm
This article has information that is wrong and unsafe: "It means that it will trip off if the current is higher than 40A (3 phases)".
RCCB/ELCB/GFI can only protect against current leakage, and does NOT have the component to protect against overload/overcurrent.
The 40A is the rating that the RCCB can safely operate in. Use a load greater than 40A on this RCCB, and it will simply overheat and melt. The RCCB will NOT trip.
MCB is the breaker that protect against overload/overcurrent.
The 40A overload rating on a MCB is simply a nominal rating, does NOT mean it will always trip at above 40A. The overload component is thermally triggered with respect to time, which is another rating on the MCB (whether it is Type B/C/D curve).
The 6/10/15kA overcurrent rating on a MCB is magnetically triggered for protection against short circuit.
RCBO is the device that can protect against BOTH current leakage AND overload.
Thomas
August 7, 2017 at 1:01 am
Very nice article.
I recently had a an experience with a spa heater and would like to share, because in many ways it was similar but also a very different and potentially dangerous situation.
We have one of those Bestway Lay-x-spa inflatable hot tubs that are popular in the UK. We're in the US so it goes here by Coleman. This is the kind with the "egg" that contains the pump, bubbler, controller, and heater.
We had a big and sudden thunderstorm, during which the unit was mistakenly left on and the GFCI breaker on the plug tripped. After the storm, the unit tripped the breaker constantly. Tests indicated it was only tripping when the heater was turned on.
I have some experience with electrics, so my son and I resolved to disassemble it and see if we could find the problem.
Inside the unit there is a ceramic heater embedded in an aluminum tube that doubles as both water pipe and heat sink. The heater contains two elements which are comparatively compared to grill or space heater elements.
Unlike your grill, the unit has electronic controls, so we can't simply test resistance at the plug. We took the heater block out and tested both elements with a multi-meter. After figuring out that our first digital multi-meter might be faulty, we were able to test them both at between 80 to 90 Ohms each. To me this seemed a bit low, as tear down videos on YouTube showed other people getting about 250 ohms resistance.
Having some experience with heaters and doing basic research I suspected current may be leaking from the elements and tripping the GFCI. Finding that replacements parts would have to be purchased on the secondary market and imported from UK (on the slow boat), we talked about running the unit disconnected ground, or un-wiring one of the two elements as possible options.
All of these options are a bit risky. The nature of water heaters makes it basically impossible to do tests without the unit connected to water and the pump running. Playing with water and electricity should not be taken lightly - even by experts. We resolved to err on the side of caution and do as many tests as possible.
We put the unit back together in its original configuration and connected it to the spa. We were surprised and delighted to see that now the unit magically stayed on with the heater running - at least for a time. My guess was that the work we did gave some moisture in the heater time to evaporate, or that possibly the GFCI itself had become oversensitive.
Being frustrated that the unit was now working better but still not long enough to heat the pool, we opened it up and disconnected the ground lead only from the heater block itself. The rest of the unit is still grounded. In this configuration the heater runs for hours without tripping the GFCI. This makes me believe the issue is only with current leakage like your grill and not the GFCI plug itself, though the plug does get warmer than I'd expect.
Now of course, chlorinated water is an excellent conductor, and the pump is pushing water right through the aluminum block which is leaking current, so we're keeping the cover on the unit and everyone is warned to stay well away. It cannot safely stay in this configuration forever.
The idea here is similar to yours, that running the heater a while and letting it get hot should "cook" any moisture out of it. We can't put the unit in the over and heat it externally without risk of melting the wire insulation, so that's out.
Ultimately, will it work or not work, who can say at this point. I guess we'll know in a day or two. Needless to say nobody will be jumping in the tub while the ground is disconnected. As we wait for a replacement part to travel halfway around the world, it also makes sense to drop into the local hardware store and purchase a replacement GFCI plug for under $20 just to be certain.
Anyway, thanks for your well written article. It confirmed my understanding of our problem, and it helped my son develop a better understanding of what we were doing and why, as well as the purpose and mechanism behind the earth-fault interrupting circuit. Well done.
Also, to anyone out there with a Lay-z-spa or other consumer grade hot tub who sees a problem like mine, for god's sake, be careful and don't try to do anything with your unit that might not be safe. Otherwise you may be in for quite a shock!
Thomas
August 7, 2017 at 1:08 am
Oh and I should clarify: above I meant that our heating element was "comparatively small compared to the one in your grill" and "we can't put it in the oven because it'll melt the wires. Sorry if my poor proofreading skills caused any confusion.
Thomas
August 12, 2017 at 9:48 am
Welp, in the end after many tests, the heater ended up tripping the breaker by drawing too much current. I guess you can't win 'em all. We'll wait for replacement parts to arrive from the UK. lol
Steven
November 19, 2018 at 1:43 am
Hi i have a convection oven it trips the house on grill function so i did the test on the plug like u said and even directly on the heating element itself. I get infinite reading on the earth n live plug. Continuity on the element n NO SHORT to earth with my multimeter. But wen i reconnect back the earth cable at the plug n after few second of heating up the hse trips again....is my grill element faulty?? This happends ONLY ON MY GRILL FUNCTION.pls advice sir
Terry Seal
January 12, 2021 at 7:46 am
Well, thanks for the heads up, I studied at college electrics and these RCD's came in after I left. Most leaflets talk in a weird explanation. Nicely explained and now fully understood. I have a dishwasher playing up and this is due to the insulation of the heater coil rusting and as it is heating water, when cooling down soaking up the water and creates the earth leakage. Pop goes the rcd. Thanks for clearing my mind.