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Earth leakage not working when mains down


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Hallo Gents,

Can someone enlighten me on this issue, I have a plug tester showing correct plug wiring and correct earthing. When there is power 3 lights are on and all good. But when there is load shedding or I turn off my main feed the earth leakage light goes out. I do this test on a plug that is coming from a solar inverter that is wired into the db’s earth and neutral and live going through a cb. 
 

Where do I start looking?

Thanks!

Dion

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38 minutes ago, dionvdberg said:

Can someone enlighten me on this issue

for most inverters you'd need a earth leakage trip switch after the inverter as well as a relay, that connects neutral to earth on the output side of the inverter, once the commercial input power disappears... you would not have the relay in place else your check would pass... and possibly not the earth leakage trip switch either... which, if this is not in place either would not make the installation safe, both are pretty much needed to make the setup as it should be... but hey, I ain't an electron pusher, check with an electrician to confirm...

Edited by Kalahari Meerkat
speeling... :-)
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On 2022/07/13 at 12:38 PM, PowerUser said:

Do you have an EL after the inverter?

I do have an earth leakage after the inverter yes, separate to the main earth leakage. And the earth runs to the earth bus bar in the main db. 

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27 minutes ago, dionvdberg said:

I do have an earth leakage after the inverter yes, separate to the main earth leakage. And the earth runs to the earth bus bar in the main db. 

on the output side of the inverter, you would need, when commercial power is down, have a connection between earth and neutral, else the earth leakage circuit breaker is unlikely to ever be able to trip.... in effect the earth leakage current is the difference between live and neutral currents, if something goes wrong and some current goes from live to earth, rather than neutral, this is when the earth leakage circuit breaker will activate and disconnect live and neutral/trip, assumption here is that the amount of current flowing from live to earth is large enough in magnitude to trip the earth leakage, usually 30 to 60mA, I think...

back to the connection between earth and neutral, this is usually done by letting the inverter control a relay that makes this connection between earth and neutral, since this bridge/connection should not exist, when commercial power is up, as far as I know...

Edited by Kalahari Meerkat
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It remains an interesting point. Apart from the portable inverters I find most people want to add the neutral to earth bridge or relay. The inverter is meant to do this internally the moment it feeds from battery when grid is down. Part of the bypass circuit when using grid to load and when feeding from battery when no grid present. This is how it works on my Axpert. My E/L works fine from grid or battery. E/L should also trip when using a line voltage tester and testing from L to E. The old coil type with the 2 neon filaments.

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I allso have a Axpert inverter, E, L and N is wired via a earh leakage cb to the main db box that has another earth leakage cb. The earth is ran from the inverter all the way to the earth busbar in the main db. 
 

Scorp007, how is your axpert wired i to the main db? Is there a seperate ground somewhere?

My next step is to add my gennie via a ats to the db, but what to sort out this earth first.. 

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11 minutes ago, dionvdberg said:

I allso have a Axpert inverter, E, L and N is wired via a earh leakage cb to the main db box that has another earth leakage cb. The earth is ran from the inverter all the way to the earth busbar in the main db. 
 

Scorp007, how is your axpert wired i to the main db? Is there a seperate ground somewhere?

My next step is to add my gennie via a ats to the db, but what to sort out this earth first.. 

For the AC I only use 1 DB. Only 1 main earth, 1 neutral. When on grid transfer connects to neutral. When on battery this is disconnected and inverter neutral is connected. When going on inverter high loads are manually disconnected. If heat pump is needed during day with good incoming PV I just switch it's MCB on. I had to use battery power twice to give the geyser a splash and dash from batteries. Only use 1 E/L on grid and inverter power. I don't use the bypass as our loads are too high.

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4 hours ago, dionvdberg said:

I may be misunderstanding you, how do you switch the earth when on bettery or eskom?

No the earth from the grid stays connected at all times. Normal 2 pole transfer switch used for L and N.

Edited by Scorp007
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26 minutes ago, dionvdberg said:

Thanks, have you actually tested with a plug tester to check if a plug trips when you are on battery/inverter? Allso, do you have a ground spike earth somewhere allso?

No have not tested with lights. I have tested the E/L for tripping from plugs. In our area earthing of grid is very good. Also no earth spike. I have always relied on my line tester(over 45yrs) to check for power and E/L. As soon as you press the button to get the volt reading when measuring L to E you causing an fault to earth and the current in the L does not go back via the N and the E/L should trip. Tester indicated AC or DC. Testing between any 3 points and knowing what value you should get takes the place of a tester with signal lights. Old school.

In the '70s these testers were black and later changed to orange in colour.

IMG_20220716_200818.thumb.jpg.bad153ed9afeee58c694e74345c9a6af.jpg

Edited by Scorp007
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On 2022/07/13 at 12:10 PM, dionvdberg said:

Where do I start looking?

A quick indication will be to test the voltage at one of your socket outlets when on inverter mode. You will get about 220V between Live and Neutral and from Live to earth about 110V and from Neutral to earth again 110V if this is your voltage it mean you need a earth/neutral bond to get rid of the 110Volt and that should should solve the problem to get the earth leakage to trip on earth fault.

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Posted (edited)

Thanks Gerrie, I assume the same test goes for installing a gennie into the db? I’ll connect it via a auto transfer switch but will probably allso have to tie earth/netral. 

Edited by dionvdberg
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Hi

I have included a drawing of how to join neutral to earth if the inverter does not do it.

This is only if the earth leakage is after the inverter.

 

I have also included a drawing of a test resistor to test if the earth leakage is working.

The resistor is a 4K7 10watt resistor (47ma) which is connected to live and earth on a 3pin plug. 

A normal earth leakage trips at about 30ma so this setup will trip it and I have tested it.

If it does not trip the earth leakage switch plug off as the resistor will get hot.

I hope this will help.

 

Earth neutral bond and EL test resistor..jpg

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3 minutes ago, dionvdberg said:

I assume the same test goes for installing a gennie into the db?

I’m not 100% sure on generator some generators might have a permanent neutral and earth bond already installed. You would need to also test the genny power to confirm if it is the case.

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Can someone explain to me why you can't just bridge the earth/neutral on the inverter with a hard wire and not bother with the relay/contactor? 

Does it mess with the Earth Leakage? 

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4 minutes ago, Sc00bs said:

Can someone explain to me why you can't just bridge the earth/neutral on the inverter with a hard wire and not bother with the relay/contactor? 

Does it mess with the Earth Leakage? 

Because you must remove it when on the grid. Otherwise you are creating a N to E bridge for the whole suburb. That wire loop will just melt off with dire consequences.

Edited by Scorp007
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4 minutes ago, Sc00bs said:

Thanks Scorp007

Isn't the Earth & Neutral supposed to be bonded coming from the Grid? 

 

Yes but what when it gets hot and does not make good contact. Or after maintenance and someone disconnected it while testing and does not put it back. We even see guys on the grid side swopping a phase and N.

Edited by Scorp007
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Hi

I found a good explanation on the web for why you should not join neutral to earth at your DB or permanently at your inverter.

"Why not short neutral and ground locally?

What happens if a neutral wire breaks upstream? Everything else downstream of the wire break is trying to return current via neutral. So all that current from all those machines travels the neutral wire to your illegal short, hops to ground, and takes ground back to the main panel, via the official neutral-ground bond, back to source. This means many amperes of current are coming through your little plug. Neutrals don't have fuses, so this burns your house down.

What if a ground wire breaks upstream? Normally if a neutral wire breaks, current can no longer return to source, and this has the effect of "floating" the neutral wire at line voltage. If you have also bridged it to ground, now you are also floating the grounding system at line voltage, at least on your machine. Anybody who comes in contact with that gets shocked.

What if both neutral and ground take a hit? Similarly what if all wires are cut, and the machine has capacitors, or inductive kickback as it spins down? Again neutral floats up toward line voltage which the system would be able to handle normally. Your bootleg bonding means ground floats too, and shocks people."

 

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5 hours ago, Sc00bs said:

Can someone explain to me why you can't just bridge the earth/neutral on the inverter with a hard wire and not bother with the relay/contactor? 

The problem is that some of the neutral (load) current will flow through earth conductors. They are not designed for current flow except in emergencies, but also the active and neutral currents won't balance, causing nuisance tripping of residual current protective devices. 

5 hours ago, Sc00bs said:

Does it mess with the Earth Leakage? 

As above, yes, via nuisance tripping. These faults can be difficult to track down. 

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