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Earth Leakage tripping


RhysMcW
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Hi All,
My InfiniSolar inverter seems to be causing the earth leakage on the utility grid side to trip.
I can't confirm this but it seems to be when the inverter is supplying a power to it's load, and pulling from the grid supply.

Any ideas what the issue could be?

Edited by RhysMcW
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Ill give you some tips to check.

Note im not an electrician, I only have a fair amount of electrical knowledge.
Infinisolar is an axpert correct?
How does your inverter get power? Does it get power from  a feed after the earth leakage?
Is the output Neutral and earth bonded together on the inverter?

If the above holds true when the inverter is in bypass mode,the bond between earth and neutral will cause the earth leakage to trip.
From what ive seen the inverter needs to be powered after the mains breaker, before it goes through an earth leakage and the output of the inverter needs its own earth leakage.

From what ive seen its i difficult scenario having the install both correct, safe and compliant with SANS.

 

I repeat, im not an electrician. bu shed some light on the wiring configuration and someone will help.

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Thank you for the reply Gielie

13 minutes ago, Gielie said:

Infinisolar is an axpert correct?

The Infinisolar and Axpert are made by the same manufacturer (Voltronic), the Axpert being an off-rid inverter and the Infinisolar being on-grid (think my terminology is about close).

13 minutes ago, Gielie said:

How does your inverter get power? Does it get power from  a feed after the earth leakage?

Yes, the grid power enters my utility DB directly into the earth leakage and then on to an isolator (I expected this to be the other way round)

16 minutes ago, Gielie said:

Is the output Neutral and earth bonded together on the inverter?

not as far as I know, but not entirely sure how to confirm.

 

18 minutes ago, Gielie said:

From what ive seen the inverter needs to be powered after the mains breaker, before it goes through an earth leakage and the output of the inverter needs its own earth leakage.

I would've expected to feed the inverter after the grid earth leakage, for protection?
I do have an earth leakage on the output side.

Here's a basic diagram of my setup
image.thumb.png.edbcec9dbf6c636bf9cde50c2558d898.png

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I could be wrong about your specific model inverter.

But the axperts do not do neutral - Earth bonding for you like the Victron units do.
In a typical install it is on in the "inverter DB" 
You have to check, but it should be on the inverter output before the inverter earth leakage.
 

Does your DB Utility DB have a split Mains and earth leakage or only an earth leakage.
If it only has an earth leakage, you are going to have to do some work,

When the Inverter switches to bypass, the N-E bond creates a short to earth and will make that earth leakage trip as it is feeding the inverter.
There are lots of threads about axperts and "N - E" bonding.
 

This is a good thread and shows you a typical wiring diagram including the N-E bond for the inverter output.
If you look at that sketch, the inverter is powered after the mains breaker and before the earth leakage to prevent this from happening.

On newer model Axperts, they have a dry contact relay that can be used with a "grounding box" to only have the neutral earth bond active when running from PV/ battery.

I suggest you do close inspection on your exact wiring and so some reading regarding the N - E bonding.

Edited by Gielie
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1 hour ago, Gielie said:

But the axperts do not do neutral - Earth bonding for you like the Victron units do.

They do. Well, it depends on the model. Earliest models didn't. Then there was a firmware update and a certain setting  could be changed to use the dry-contact relay in the inverter to operate an external bonding relay. And then finally, they changed the relay they use so it could bond TN when running islanded.

The bonding relay will generally open before the inverter reconnects to the grid, so I doubt it's a bonding relay issue. When connected to the grid the bonding relay should be open. If not, then that is the cause of the tripping.

99% of the time a tripping RCD is because you have a leak to earth. You simply have to find it. You do this by disconnecting circuits (on the output of the inverter in this case) until the tripping stops. You usually have to disconnect both the live and the neutral, so generally this is best left to an electrician. You switch off all the live breakers, and disconnect all the neutral wires from the neutral bar. Be areful, since those hanging-in-mid-air neutral wires could be carrying live current while you're messing around like this. By bringing the circuits in one by one you can usually find the culprit.

You could (should?) also do an insulation resistance test. Again, that helps to find the circuit with the leak.

But, in the last 1% of cases, it could be that your "standing leakage" exceeds 15mA-20mA, where most RCDs starts to trip. Most modern appliances leak a small amount to earth, usually because of the EMI filter or surge arrestor that sits between the L, N and E conductors. This is usually in the order of maybe 1 or 2mA, so not a problem, but if you have enough appliances on the RCD it tends to add up and eventually you get nuisance tripping. In this case, you will usually find that the tripping stops if you unplug all your appliances, and comes back once enough of them are plugged back in.

I really honestly truly hate chasing RCD trips. I find that an earth leakage clamp meter (essentially an AC clamp meter that can measure the residual current) helps a LOT to chase down such issues. Especially compounding standing leakages...

But, as I said... got to start with the 99%. In 99% of cases, it happens because something is wrong...

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This is my earth leakage clamp meter. Here I'm showing the rather terrible situation in my own house at the moment. I have a 13mA standing leakage...

leakage.jpeg.2859b1ce197e7e1c0bb3ce99ca0364db.jpeg

And this morning I had an oil heater that tripped an RCD repeatedly too. Ignore the ET112 in the picture... that was just the easiest cable I had lying around where I could reach the earth conductor easily. This heater will gradually increase leakage as it heats up, and then trip the RCD.

heater-leakage.jpeg.01e3aa9084c1ec78b9ebcfbba3673b48.jpeg

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@Gielie, thank you for those post links, have read them and found a few others around, not sure I really understand much of it but do believe I need to move the inverter input feed from after the RCD to before it (grid side). This will mean doing some rewiring to put a main switch/isolator before the RCD as currently the grid supply goes directly into the RCD first then to the main switch.
I may just replace the RCD while I'm at it as it's very old anyway and I see the new CBI ELs are narrower which would create the space I was after for an additional CB too (very old DB with metal cover and limited CB space)...

@plonkster, thanks for the info, gives me more to consider too.I had actually done that testing you mention by disconnecting the load circuits, including neutrals (insulation tape became my friend), not because I really knew what I was doing but it was just something to try to isolate the issue. I discovered that no matter which circuit I connected the grid side RCD still tripped.

I've read about the Axperts, older and new ones regarding the N-E bonding... One would expect that if it is needed that the inverter MUST take care of it at the appropriate time, as the new Axperts seems to. I rechecked my Infini manual in case there was mention of N-E bonding requirements but it only mentions to install a CB on the input an recommends an isolator on the output...

My current game plan is to probably replace the grid side DB main switch and RCD and have the grid connect first to the main switch, then on to the RCD with a connection to the inverter between the main switch and the RCD (already have a CB near the inverter on the input).

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Quick question (hopefully)..
If I'm replacing my RCD I see there are 2 options (with CBI anyway) - with and without overload protection.
Am I correct in assuming the with overload protection would be current draw based, like CBs, as well as the EL and therefore if I'm going to install a main switch that handles the current overload I can go with the without overload protection unit?
There is a significant price difference, the "with" option being around 2.5 times more costly. I'm looking at CBI as that's what mostly in the old DB (not DIN rail) and I believe the brand is good.

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21 minutes ago, RhysMcW said:

if I'm going to install a main switch that handles the current overload I can go with the without overload protection unit?

Indeed. The combo unit does both, but it is quite common to use two breakers to get the job done.

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4 hours ago, plonkster said:

Most modern appliances leak a small amount to earth, usually because of the EMI filter or surge arrestor that sits between the L, N and E conductors. This is usually in the order of maybe 1 or 2mA, so not a problem, but if you have enough appliances on the RCD it tends to add up and eventually you get nuisance tripping.

I had regular nuisance tripping until I removed all of the surge arrestor type plugs & power strips in our house. So far we've had a single trip this whole year. If you live in an area where there's no lightning at this time of the year, it may be a worthwhile test.

For the clever folks: there's a surge arrestor on the AC going from the DB to my inverter. I am not sure if its purpose is only to protect the inverter, or whether it cascade some protection to the stuff downstream?

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1 hour ago, plonkster said:

I still want to do an experiment with that and perhaps turn it into a video. I want to add 14D431K MOVs until the RCD trips. I also want to test and demonstrate what happens when the TN bond is temporarily disconnected and reconnected, as is done by inverters when they do their relay test.

They are R10 a pop. If the leakage current graphs are to be believed you'll need around 10 millionish of them for 20mA.

Rather made a Hollywood blockbuster😷

image.png.2daa4ca582b9139fc248fe0d17f01148.png

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1 hour ago, phil.g00 said:

They are R10 a pop. If the leakage current graphs are to be believed you'll need around 10 millionish of them for 20mA.

The transient when bonding/unbonding TN is much higher. At least, there is a reason I have that one in mind. I had a garage door opener that had three of them in, and it seemed to add just enough to nuisance trip the RCD. So I may not be able to create enough of a standing leak, at a couple of pF or so, but I think it has potential... 🙂

The garage door opener since broke... and I kept the bits and pieces. Also, I now have a decent storage scope... so maybe I can just do that instead.

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10 minutes ago, phil.g00 said:

@plonkster, I look forward to the video, but aside from a blown MOV, I think you're chasing your tail.

 

I'm not so sure. MOVs have a small capacitance, which doesn't cause much current to flow at 50Hz, but the current through a capacitor depends on the rate of change of the voltage across it, using the equation I = C.dv/dt

So a transient with a high dv/dt can cause much more than normal current to flow. If the earth leakage breaker is very sensitive or already close to it's limit then such a transient can cause it to trip.

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58 minutes ago, Stanley said:

MOVs have a small capacitance

Indeed, this is what I suspect to be at fault.

53 minutes ago, phil.g00 said:

yet still I doubt.

All I can tell you, is that i did an empirical test:

1. I unplugged the garage door opener, and interrupted the power, forcing the inverter to do a relay test. The RCD did not trip.

2. I plugged in the garage door opener, did the same thing, and the RCD tripped.

Obviously it did not do it on its own, but in collaboration with all the other leakers that's already in the house. The gate opener was on the same circuit. I recall the leakage was not insignificant, but I never measured it separately.

44026573_10156534809275619_1659529355484725248_o.thumb.jpg.54f99ec589b4865061a88ebd5ef9a6aa.jpg

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3 minutes ago, phil.g00 said:

It may well be an MOV, but it's blown if it is.

I would expect a blown MOV to be a problem all the time, not just during a transient (when the inverter is doing it's relay checks).

I have seen MOVs blow before and they usually destroy themselves quite nicely. I have also seen MOVs that became a short circuit and blew fuses, while the MOV itself still looked ok physically. I haven't yet seen one that was only partially blown and would cause weird issues like this, although I suppose it could be possible.

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28 minutes ago, phil.g00 said:

I am doubting your explanation of a healthy MOV, get a megger and you'll find the problem. Not all faults can be found with an AVO.

Since then, my collection of testing kit has expanded somewhat. I actually have an insulation tester now. And I've learned that 99% of the time, an RCD trip is because you have an insulation problem somewhere. It's been a bit of a quest of mine to understand the remaining 1% 🙂

(Next bit of kit I want... a current probe for the scope. Man these things are expensive. For now I'm using a CT with the normal voltage probe... technically the same thing, if a bit crude).

Edited by plonkster
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2 minutes ago, plonkster said:

For now I'm using a CT with the normal voltage probe

Sounds perfect for AC use only. If you choose the correct burden resistor for the CT you can get a nice scale (i.e. 1mV/A or 10mV/A etc.) that will allow the scope to show you the actual current in amps so you don't have to calculate anything on the fly.

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Just now, Stanley said:

Sounds perfect for AC use only. If you choose the correct burden resistor for the CT you can get a nice scale (i.e. 1mV/A or 10mV/A etc.) that will allow the scope to show you the actual current in amps so you don't have to calculate anything on the fly.

Indeed, which is why a proper current probe is on my wishlist. Makes it so much easier, especially when you apply the Math function, it can show the right unit (VA) instead of V^2.

Speaking of scopes doing the right thing. I have an ancient (in the 90s it qualified as high end) Kenwood analog scope. It auto-detects probes, eg if you put on a 10:1 probe, it knows it automatically. Two weeks ago I acquired a brand new Keysight scope. Even though entry level, I was surprised to find that it does not have this feature. You have to manually select the attenuation. But I'm not complaining, it is an impressive scope for the money. It's an EDUX1052 (the edu means this is the castrated one they make for education places).

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2 minutes ago, plonkster said:

Speaking of scopes doing the right thing. I have an ancient (in the 90s it qualified as high end) Kenwood analog scope. It auto-detects probes, eg if you put on a 10:1 probe, it knows it automatically. Two weeks ago I acquired a brand new Keysight scope. Even though entry level, I was surprised to find that it does not have this feature. You have to manually select the attenuation. But I'm not complaining, it is an impressive scope for the money. It's an EDUX1052 (the edu means this is the castrated one they make for education places).

The probe auto-detect function is quite nice most of the time. It usually only works with the probes that support it as well. I am lucky enough to work with some decent Agilent scopes that have it. You can see a small conductive area around the BNC connector, and a little spring loaded pin on the probe that touches it. It's probably just passive, I would guess. There have been a couple of times when I explicitly didn't want the auto-detect feature (like when using a voltage probe and CT to measure current), so I just stick a little scrap of paper between the pin on the probe and the conductive strip on the scope to disable it. Then you can set it as a current measurement and use the math function to get power.

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