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Earth leakage trips intermittently - cannot find reason


Antony
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Over the last 4 days I have had 4 earth leakage trips.

Friday afternoon at about 3pm, Saturday at 11am, Sunday at almost midnight and again this morning at about 6:40am, so the incidents are not consistent.

2 of these incidents I was close to the DB and pushed up the trip switch almost immediately and it stayed on.

I'm unable to determine why this is happening.

If there was an earth leakage somewhere surely the trip switch would keep tripping.

Could this be caused by something on the grid side, I noticed about a month ago when we had a power outage, that when it cam on the earth leakage tripped almost instantly.

I saw the lights flash and heard the telephone handset beep start, then it tripped immediately.

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26 minutes ago, Antony said:

If there was an earth leakage somewhere surely the trip switch would keep tripping

Not always, from time to time you can get a intermittent earth fault, but in most cases it will progressively get worse over time to a stage where you can not reset it anymore. I saw that a lot with outside or garden light circuits and outside plugs. One of my worst cases at a clients house were ants walking over an exposed neutral wire in a damaged Surfix cable. The ants created a path for the current to flow between neutral and the screening of the cable. Took me weeks to find because it was intermittent. Another example was a Gecko in an outside plug and once i had a Millipede  under the PC board in the power supply of a gate motor doing the same. Its back end was fried to the PC board where the 220V came in but dried out from the current, but as it tried to move, it made contact and tripped. Found it after 2 days and the Millipede was still alive. 

Secondly. You might have a neutral breaking through on a light circuit or plug circuit creating a very small leakage, and then when a heavy load like a geyser  or  Stove switches on the amps in the neutral wires increases and aggravates the situation, causing the leakage to increase and subsequently trip the EL. I think this might be the reason, it will also explain why the El trips as the Power is restored after an outage. Powering up everything together is quite a load and the change of a small leakage showing itself is good. 

Thirdly , Earth leakage  units does pack up from time to time and start giving you nuisance trips. Please dont just replace it, as this might not be the case in your situation . They are pretty expensive and replacing them just to find out the problem persist, is not nice. 

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4 hours ago, Antony said:

Could this be caused by something on the grid side, I noticed about a month ago when we had a power outage, that when it cam on the earth leakage tripped almost instantly.

It could be caused by something on the grid side, though it is unlikely. I read at least one post somewhere on a forum where the trouble was in a lamp post on the street.

One thing it could be is that the RCD is simply on its way out. I had that once, some years ago. They have an electrical life, how many times they can operate, and for the cheap ones this could be a few thousand times. So you could just replace the RCD, its a cheap R250-R350 and it probably needs to be done anyway at some point.

(RCD == Residual Current Device, the more formal name for what we informally call an Earth Leakage).

It is also possible that you have what I had: You have all sorts of EMI-filters and surge arrestors in appliances in your home, and this causes a high standing earth leakage.

Let me first take a detour to explain standing leakage: Every house has a standing leakage to earth. There is always a couple of microamps (or even millamps) sneaking off to earth, because insulation is never perfect, some of it always finds alternative ways back to the supply and therefore bypasses the normal return path that is monitored by the RCD.

Most RCDs start tripping at around their 50% rating. So a 30mA RCD might trip as early as 15mA. The regulations simply state that they MUST trip within a very short time at 30mA.

Then inside your home you may have appliances that introduce more such leakage. One way to filter out EMI, for example, is to fit two capacitors between L/N and earth (and a capacitor is a frequency dependent resistor, so it passes a small bit of current to earth). The other culprit is the cheap-but-effective surge protection used almost everywhere: Metal Oxide Varistors. They pass a tiny bit of current too.

Now I can get to the meat of the argument: Sometimes when the power comes on, these filter devices can introduce a small spike (duration is literally in the microsecond range) and this causes nuisance tripping, especially if it is on top of a fairly high leakage. There is no actual leakage (other than the normal tiny bit of standing loss).

In my home I had a standing loss of a good 7mA.

44026573_10156534809275619_1659529355484725248_o.thumb.jpg.ed30928ea2ea405e5797c6d4bfc113cc.jpg

It took me weeks to solve it. These are the things I uncovered.

41922911_10156473202760619_6831740783935094784_o.thumb.jpg.eb92aba4603bad4683ee0b2414b13a38.jpg

This is the plug of a "Multiplug strip", with a surge arrestor built in. Note the MOVs (those green things). This introduced a good 1mA leakage. One of the neon lamps were burned out in any case, so I removed it.

44052883_10156539543745619_1922839584060735488_o.thumb.jpg.7000cbae672c3bd150d07840bc9fc97c.jpg

That's the transformer feeding the alarm system. It has a big EMI filter in front of the iron transformer (for what? Iron transformers don't introduce noise and are pretty effective at removing it... I ripped it out).

surge2.thumb.jpg.98489100a27bcdd05e0d7f11ee6609ee.jpg

That's the bottom side of the Garage door opener (ET DC-Blue). Again note the blue MOVs.

How did I find these appliances? Trial and error. Literally unplugging everything, faking power failures and first drilling down to which circuits had the problem, and then further down to the appliances. All the while the kids are unhappy because the internet is down ;-)

And my solution...

44731917_10156558072885619_3896920155187314688_o.thumb.jpg.fa6a19d149c675ba7a831d546f0fd1a9.jpg

This is a type AP-R (ABB's lingo for impulse-resistant) RCD. I paid too much for it. It should cost about R1200, but apparently it is out of stock with the suppliers at the moment. Contact the guys at LiveCopper to find out how long until they have stock.

Edited by plonkster
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Also see this question on stackexchange. These impulse resistant RCDs are more than ten times more resistant to 8x20µs transients. With today's electronic loads that almost all pack a noisy SMPS and some EMI filters, I think it is a good investment anyway. The last thing you want is a nuisance trip while you're on holiday and a defrosted freezer full of rotten fish when you get back (thankfully I'm not a fish person... but some people are).

I also ended up splitting the house in three, sort-of as a side-effect rather than planned. The geyser and kitchen is on one RCD. The lights are on a second. And the rest of the circuits (with inverter backup) are on a third. I heard a rumour that new SANS regulations ill require the Geyser to have its own RCD. Why? Apparently heat pumps cause nuisance tripping sometimes... :-)

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25 minutes ago, plonkster said:

This is the plug of a "Multiplug strip", with a surge arrestor built in. Note the MOVs (those green things). This introduced a good 1mA leakage. One of the neon lamps were burned out in any case, so I removed it.

I'm going to start with removing all surge arrestor type multi plugs. Its going to be a long process of elimination.

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Just now, plonkster said:

The last thing you want is a nuisance trip while you're on holiday and a defrosted freezer full of rotten fish when you get back (thankfully I'm not a fish person... but some people are).

I'm going to Rooiels for the holidays so I need it "fixed" before

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Something else I did: I made a small extension cord and exposed the earth conductor, then cut it and connected to two terminal blocks so I can wire a multimeter inline. Plug this between the wall and the appliance you want to test. Start the DMM in the high milliamp range. That should show the leakage on the earth conductor for that appliance.

Downside: Unless you have a true RMS meter, what you see is an average value, it does not account for non-linear noise as introduced by some devices. Also not that easy on fixed circuits. Which is why I bought the clamp meter (its true RMS as well). Nevertheless, it's an easy cheap way so that you are not flying completely blind.

I spent too much money on this... but I consider it school money, it is sort of my business (R & D), and I always wanted a good clamp meter anyway.

Also see this:

 

Edited by plonkster
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1 hour ago, plonkster said:

 

44731917_10156558072885619_3896920155187314688_o.thumb.jpg.fa6a19d149c675ba7a831d546f0fd1a9.jpg

This is a type AP-R (ABB's lingo for impulse-resistant) RCD. I paid too much for it. It should cost about R1200, but apparently it is out of stock with the suppliers at the moment. Contact the guys at LifeCopper to find out how long until they have stock.

I see this one is a 25A My main (very old) EL is a 60Amp

20181119_114825.jpg

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@Antony, the main thing on your earth leakage CB to look out for is the leakage current. Seems like 20mA there.

Are you sure that you don't have a neutral somewhere touch the earth inadvertently?

What I found is oxidation (rust) on the top of my oven connectors. The neutral wire had melted(!!!!) partially and started to rust. This in turn caused a periodic leak to the earth and subsequently gave me erratic trips. 

Has the frequency in tripping shorted (happened more often) or could it be ok for a week and then trip?

 

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4 minutes ago, Atti2de said:

Has the frequency in tripping shorted (happened more often) or could it be ok for a week and then trip?

 

Yes it seems to be more often, but only of late. It used to happen maybe twice a year, now I have had almost 6 in the last 3 weeks. 4 of which was since Friday.

The times of the day also makes no sense. This morning nothing was on other than the usual fridge cellphone chargers etc.

No geyser, etc. no heavy loads at all.

Edited by Antony
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1 hour ago, Johandup said:

What is not mentioned are the cell phone usb chargers which we have in abundance in all our homes.

We have this tendency to leave them plugged in - and they are all made by the cheapest manufacturer. And we trust they will last foreva..

but would a usb charger contribute to earth leakages. I thought it had to be a device with an earth connection. All my chargers are 2 pin type charges.

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35 minutes ago, Antony said:

but would a usb charger contribute to earth leakages. I thought it had to be a device with an earth connection. All my chargers are 2 pin type charges.

In theory it could, but there has to be a path to earth somehow. Imagine this scenario: There is an internal short of some kind from the live to the negative pin on the USB side, and it is plugged into your phone. You accidentally touch the rim of the earphone jack (which internally has a path to USB negative) and the current now has a path from live to earth. The RCD trips, saving your life.

That is an example of an earth leakage without an earth connection. Extreme example that probably does not apply in this case. When operating correctly, then yes: Those chargers can't have a standing loss to earth, as it has no earth connection.

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6 minutes ago, Antony said:

but would a usb charger contribute to earth leakages. I thought it had to be a device with an earth connection. All my chargers are 2 pin type charges.

Valid point - not for two pin types.

When I do switching on my backup system I switch the rcb first off as it is my experience that it will always trip when the power comes on - similiar to yours. 

It is a nuisance as the power can fail during an outing when I’m away. Up to now I have not come across a solution thats legal. Fitting a higher than a 35ma rcb will solve it (done regularly in other countries) but it is illegal here. I have not come across a rcb that trips at the indicated ma - most of them is out by 10ma - 20ma less (expensive as well as cheaper types) so a lower ma rating is never good. Also bear in mind that more than one load can contribute to the total leakage i.e. motors starting up. A clamp meter is of very good use here.

I have good literature on the earth leakage issues which I will post some time.

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59 minutes ago, Johandup said:

I have not come across a rcb that trips at the indicated ma - most of them is out by 10ma - 20ma

Regulations says it MUST trip within 300ms at its rated leakage current (IΔn), and in 40ms at 5 times its rated current (5IΔn). It should NOT trip at less than 0.5IΔn.

So essentially it is allowed to trip anywhere between 15mA and 30mA, and that is considered within spec. In practice, it will trip somewhere between 15mA and 20mA, but not necessarily within 300ms.

1 hour ago, Johandup said:

Up to now I have not come across a solution thats legal

The Impulse Resistant kind is legal and worked perfectly for me. It's a rather expensive RCD, yes, but only about twice what you'd pay for a decent ABB or Gewiss. Compare also to the cost of labour to find that pesky device.

I do think a peak-holding clamp meter is a good idea (maybe you can rent one?). Just so you have an idea of what the problem really is before you spend money. I really see two scenarios:

1. Your standing leakage is fairly high, above 10mA, sailing too close to the halfway mark and causing occasional tripping.

2. Your standing loss is low, so you're likely dealing with EMI filters and surge arrestors that cause a spike at power-on.

In the first case, find the appliances with the high leakage. In the second case, look at an impulse resistant RCD.

I think you're allowed up to 2mA standing loss for every 10A of consumption, although I think that is on the high side: It means the average single phase house is allowed 12mA... which is kinda close to 15mA.

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13 hours ago, plonkster said:

1. Your standing leakage is fairly high, above 10mA, sailing too close to the halfway mark and causing occasional tripping.

this is measured around the live and neutral and I'm looking for a peak of over 10mA?

According to my prepaid meter, my maximum consumed Amps is 18A, so I should not be above 9mA on standing leakage?

 

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2 hours ago, Antony said:

this is measured around the live and neutral and I'm looking for a peak of over 10mA?

You put the clamp meter around both conductors. Because the current runs in opposite directions, the magnetic fields around the conductors cancel each other out (right hand rule), so if they are perfectly balanced the reading should be zero. The meter will only see the difference between them. Usually it is best to use a clamp meter that's actually designed for leakage currents, but in theory any clamp meter should work.

What you're looking for is a low constant value. Remember that the clamp meter only samples a couple of times a second (the leakage meters sample up to 20 times a second, but the display updates less often), and if it isn't a true-RMS meter the value you get might not even be completely accurate. Nevertheless, you want a low constant value, something less than 10mA preferably.

The "2mA for every 10A" thing is a rule of thumb,  guideline, not a law :-) It's what you use when deciding how many plug circuits to put on a single RCD. It's one of those things where being OVER that limit is definitely a bad thing, but being under it isn't necessarily a good thing.

My thinking is that if you have a low average leakage, then the RCD is most likely tripping on a transient. Measuring the transient requires a more expensive clamp meter or a scope with a current clamp, so it becomes hard to DIY this test. Taking a gamble on the 1.2k RCD might pay off.

If however your average is quite high, then you might have to look at splitting up the circuits and having more than one RCD so that the leakage per group is lower.

Technically, of course, I should also tell you that it is best to let a real electrician do this work :-)

Edited by plonkster
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Thanks Earth leakage problems are notoriously difficult to pinpoint.

An expensive solution (for me) would be to use rcbo switches instead of normal overloads in the distribution board.Apparently this is becoming the norm in well to do countries. Every circuit would then have its own rcd and detecting problem circuits would be easy.

https://za.rs-online.com/web/c/automation-control-gear/circuit-protection-circuit-breakers/rcbos/?cm_mmc=ZA-PPC-DS3A-_-google-_-1_ZA_EN_G_Circuit_Protection_Phrase-_-[Adgroup]-_-[searchterm]&matchtype=p&kwd-4193448037&gclid=Cj0KCQiA28nfBRCDARIsANc5BFBmJ3wKBM31yz0eF4gMYQh_zW0pj5xSWzXiG_qscWNgPVGGt5OrW0EaAs3KEALw_wcB&gclsrc=aw.ds

Sometimes I think it would be wise to purchase one to install when you get trips. At least you willl have a better chance of isolating problems in a practical way. Just reinstall it every time when you have trips untill it trips.

And for a lot of valuable information please take the time to read this. It is all about earth leakage trips:

https://www.theforumsa.co.za/forums/showthread.php/19255-Earth-Leakage-Breaker-(RCD)-Tripping

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2 hours ago, Johandup said:

use rcbo switches

I very almost went that way. The reason why I didn't was because by the end of that exercise I had it narrowed to two appliances (electronic gate motor and garage door opener) and both of them would trip the RCD on their own. In other words, I would have spent all that money splitting it down to RCBOs, and I would have had two of them that still tripped every time. RCBOs aren't that cheap either, and to properly wire them each one needs the neutral of that circuit to be looped through the rcbo AND an earth wire attached too (at least for some makes), so it requires a bit more rewiring than just a drop-in.

So going to RCBOs would lessen the irritation, but I would still have two tripping circuits, so I would still have to find a solution to the original problem.

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On 2018/11/20 at 2:52 PM, Johandup said:

Sometimes I think it would be wise to purchase one to install when you get trips. At least you willl have a better chance of isolating problems in a practical way. Just reinstall it every time when you have trips untill it trips.

 

The weird thing is, it hasn't happened again since Monday.

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On 2018/11/20 at 2:52 PM, Johandup said:

Sometimes I think it would be wise to purchase one to install when you get trips. At least you willl have a better chance of isolating problems in a practical way. Just reinstall it every time when you have trips untill it trips.

 

The weird thing is, it hasn't happened again since Monday.

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On 2018/11/20 at 5:32 PM, plonkster said:

I had it narrowed to two appliances (electronic gate motor and garage door opener) and both of them would trip the RCD on their own. In other words,

Would that mean that your trip would only occur when these items were used or anytime?

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