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Earth leakage trips intermittently - cannot find reason


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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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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 o

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

@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?

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20 minutes ago, Antony said:

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

Have you read the theforumsa piece I’ve posted?

Something was running at the times you said it tripped, and the only thing that does that could be your fridge/freezer.

Are you aware that a fridge takes the condensation out of the compartments and drops it on top of the motor to evaporate. When a fridge is old it can rust through.

If the humidity is very high it can overflow. This is very easy to check - anyway it needs cleaning once in while to get rid of the dust it attracts.

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1 hour ago, Antony said:

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

Only happened when there was a power failure and the power came back. But it would happen every time. And in my case the Multigrid inverter is also involved: The relay testing sequence injected just enough extra transients to trip it. But it happened every time, all I had to do is flip the breaker off, flip it back on... wait for the relay test rattle... and boom: RCD trips.

Granted, not exactly the same as your situation, but still has enough similarity.

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33 minutes ago, Antony said:

The one important point that thread makes is that your first response should be to look for a leak (rather than assuming the RCD needs changing). My own answers focused a bit too much on using a transient resistant RCD, so I'm taking this opportunity to restore that balance. That's also why I suggested doing a proper test of the leakage current, so you know what you're working with.

The first step -- so I was told by more than one sparky -- is to test at what point the RCD actually trips. I have one of these:

rcd-tester.jpg.26b414c60b980f232ffa7e6aa1412e8a.jpg

With this I know my RCD trips between 15mA and 20mA. That's within spec. They cost around R250.

If the RCD trips within spec, then you have to find the leakage, and that's where things get interesting. Once you found the leakage (which is what I did after many hours), then the nature of the leakage (a transient in my case) determines the solution (a better RCD in my case).

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I experienced an earth leakage trip yesterday when I started the borehole pump.

Was successful only only on the third try - what caused two trips? Dunno as the borehole pump does not have an installed earth on it - the steel pipes filled with water might relay transient currents to the earth spikes. The pump does not start on auto so its fine.

It tripped an el cheapo rcd - what I did find was having rcds installed in series does not really work for me as the one with the most sensitive ma would trip first - even if it is in a different box (outside in this case) but feading from the same municipal main connection. I was trying to prevent a trip on the municipal side by installing earth leakages like this. But it boomeranged due to the different sensitivities from these devices which I was not aware of at the time - I returned a Hagar rcd which was replaced without a query (I told them it was tripping at 5ma!!). The most expensive one of R1200 is the closest to the main isolator.

I will have to measure the ma with my clamp meter at some time - not up to it now as I am still recovering from a back fusion operation. :-/

Edited by Johandup
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Since I installed my new Multigrid I have had a few trips on the output side, over and above the nuisance tripping during testing, same as Plonkster had.

I took the view that I can find the culprits, but what if I or anyone else buys anything new and it al starts over? It will be a constant battle.

So with the tripping without any changes whatsoever I wrote it off as CoCT power funnies that pushed the mA over the top on the output side of the Multigrid, as it is grid tied. 

To solve my problem, thanks to Plonksters efforts, I am now waiting on my ABB F202 A-25/0.03 AP-R to arrive in Des, which I found at a whopping nice price of R 1009.00 from a super guy called JP at www.livecopper.co.za

May be an idea to get the same, or bigger, or ask them for advice as come across as seriously jacked, not just another Jack.

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8 hours ago, Johandup said:

rcds installed in series does not really work for me as the one with the most sensitive ma would trip first

While reading up on this I found out there is something called selectivity, and you do this by either giving the upstream one a higher leakage current rating, or by installing a type-S (time delay) unit. If you don't do this, then either one (or both) can trip, which is of course very irritating if the upstream one is some distance away.

Of course time-delay and higher-leakage-current units are not allowed when protecting sockets in a home. What I did in my case is to install a 100mA RCBO in front of the inverter and a 30mA RCD after it. There are no other sockets fed from that circuit (before the inverter), so this gets me selectivity and suitable protection.

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Newer RCD measure the difference between live and neutral and if there is a 30mA  it should trip. In your case there might be a joint that  allows some current to escape and trip the RCD. After one or two tries the little moisture  is driven off and the pump starts.

I am now going to go out on a limb here. With RCDs measuring between live and neutral is the earth wire not superfluous. So long as the neutral is grounded what is the earth wire doing. OK earth is an alternative path for stray current. But with a RCD  tripping on live and neutral the need for an alternative pathway falls away. Ok I get if the RCD is faulty the earth then comes into play.

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On 2018/11/22 at 7:59 AM, Johandup said:

Have you read the theforumsa piece I’ve posted?

Something was running at the times you said it tripped, and the only thing that does that could be your fridge/freezer.

Are you aware that a fridge takes the condensation out of the compartments and drops it on top of the motor to evaporate. When a fridge is old it can rust through.

If the humidity is very high it can overflow. This is very easy to check - anyway it needs cleaning once in while to get rid of the dust it attracts.

some good advice, thank you

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12 minutes ago, Chris Hobson said:

Newer RCD measure the difference between live and neutral and if there is a 30mA  it should trip. In your case there might be a joint that  allows some current to escape and trip the RCD. After one or two tries the little moisture  is driven off and the pump starts.

I am now going to go out on a limb here. With RCDs measuring between live and neutral is the earth wire not superfluous. So long as the neutral is grounded what is the earth wire doing. OK earth is an alternative path for stray current. But with a RCD  tripping on live and neutral the need for an alternative pathway falls away. Ok I get if the RCD is faulty the earth then comes into play.

I have been thinking about this as well but it has to be there.

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1 hour ago, Chris Hobson said:

is the earth wire not superfluous

If there is no possible way for the live parts to come into contact with the outside enclosure, you don't need an earth.

If there is a possibility, then the outside of the appliance must be earthed, and this actually has nothing to do with the RCD. It has to do with making sure the appliance remains at the same potential as that under your feet. Imagine for example that the earth/neutral bond is lost somehow... so now both line and neutral are floating somewhere up there... depending on atmospheric conditions and similar that could be several thousand volts above earth. An earth fault in the appliance could then expose the user to an extreme voltage, but by tying all such surfaces to protective earth that can never happen.

In addition, should a rather large current take that path, you not only gave it somewhere safe to go, it will also trip either an overcurrent device or an RCD.

But let's take another angle on this. I noticed that Makita drills don't have an earth wire. This obviously means there is no possibility of me getting into contact with a live wire, the enclosure is designed in such a manner. I bet however that if I drop it into water it will trip an RCD... :-)

So basically... it is two separate safety measures that cooperate to some extent.

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38 minutes ago, plonkster said:

If there is no possible way for the live parts to come into contact with the outside enclosure, you don't need an earth.

If there is a possibility, then the outside of the appliance must be earthed, and this actually has nothing to do with the RCD. It has to do with making sure the appliance remains at the same potential as that under your feet. Imagine for example that the earth/neutral bond is lost somehow... so now both line and neutral are floating somewhere up there... depending on atmospheric conditions and similar that could be several thousand volts above earth. An earth fault in the appliance could then expose the user to an extreme voltage, but by tying all such surfaces to protective earth that can never happen.

In addition, should a rather large current take that path, you not only gave it somewhere safe to go, it will also trip either an overcurrent device or an RCD.

But let's take another angle on this. I noticed that Makita drills don't have an earth wire. This obviously means there is no possibility of me getting into contact with a live wire, the enclosure is designed in such a manner. I bet however that if I drop it into water it will trip an RCD... :-)

So basically... it is two separate safety measures that cooperate to some extent.

SANS regulations spell out which part of a house electrical installation must be connected to a rcd. Currently quite a lot - in short any electrical equipment which can be handled by a human must be earthed. Plugs are a good example as people connect equipment to it and thus are limited to 16 amps and a connection through the rcd. I think a lot of trips are caused by the practice of connecting all the circuit breakers through the rcd instead of simply complying to the SANS requirements. This gets done by electricians for the simple reason to double up on safety - read the views expressed on theforumsa by electricians.

In simple terms a rcd monitors the imbalance between the live and neutral - when it exceeds 35ma it must trip according to the SANS regulations. If a circuit is not wired through the rcd any fault will become an overload or short circuit which will either

a: trip the overload if it is the correct size for the wire size, or

b: the wire will melt.

Circuit breakers are sized according to the installed wire size.

As the live and neutral is a continuous path for any circuit to work the current flowing in it should always be the same theoretically - the only way for it to become unbalanced is when part of the current escapes via the earth connection. This can be caused by any number of reasons. So without a proper earth connection the earth leakage protection will not work. 

Edited by Johandup
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4 hours ago, Javi Martínez said:

isolated transformer

That was my next plan, if the fancy RCD didn't do it. I was going to put the garage door opener and gate motor on an isolation transformer, that is give them a floating supply, but still earth them to system ground for safety and noise suppression.

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56 minutes ago, plonkster said:

That was my next plan, if the fancy RCD didn't do it. I was going to put the garage door opener and gate motor on an isolation transformer, that is give them a floating supply, but still earth them to system ground for safety and noise suppression.

At home, I use that circuit. Insulation transformer + ungrounded neutral. If there is a failure, there is no cut, the insulation monitor advice me and i can repair whatever fails.

https://www.bender-uk.com/products/insulation-monitoring-overview

Edited by Javi Martínez
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On 2018/11/19 at 9:07 AM, Antony said:

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.

Hi Antony, did you manage to resolve your earth leakage issue? Something to keep in mind too, is that the earth leakage trips on the sum of all the earth leakages around your house. There may be more than one appliance, gate motor / borehole etc leaking, and the sum of all these earth leakages could be causing the trip. Thats why it could be so hard to find.

Something else to consider - the earth leakage may just be faulty?

all the best

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On 2018/11/19 at 9:07 AM, Antony said:

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.

Hi Antony, did you manage to resolve your earth leakage issue? Something to keep in mind too, is that the earth leakage trips on the sum of all the earth leakages around your house. There may be more than one appliance, gate motor / borehole etc leaking, and the sum of all these earth leakages could be causing the trip. Thats why it could be so hard to find.

Something else to consider - the earth leakage may just be faulty?

all the best

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On ‎2019‎/‎12‎/‎21 at 10:48 AM, jasonvanwyk said:

Hi Antony, did you manage to resolve your earth leakage issue? Something to keep in mind too, is that the earth leakage trips on the sum of all the earth leakages around your house. There may be more than one appliance, gate motor / borehole etc leaking, and the sum of all these earth leakages could be causing the trip. Thats why it could be so hard to find.

Something else to consider - the earth leakage may just be faulty?

all the best

Nope I never got to find the problem, it is so intermittent. In fact we have more load shedding incidents of late than rouge trips.

Touch wood, It hasn't happened for a few months now.

Edited by Antony
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