Neutral earth bonding on backup systems.

[GCE]

So this morning I was called out for an inverter tripping on overload intermittantly.

After much testing, I found that when the geyser is on, the output reading on the inverter goes up to over 4Kw even although the geyser is not fed by the inverter.

Whilst getting this reading of 4Kw, I put a clamp meter on the inverter output and it was only supplying 1,5 A (+-340W). The electronics of the inverter was somehow reading the current drawn by the geyser even although it was not supplying the geyser. It was time to call a friend.

The problem dissapeared when the permanent neutral earth bond on the inverter output was removed. As soon as it was replaced, the fault showed up again.

A couple more tests were done and it was found that everything was A ok when the earth neutral on the inverter is ONLY bridged whilst in islanding mode. The current in the earth neutral bridge was 10,5 Amps.

Anyway, thought I,d mention the above in case anyone comes across the same fault one day.

Moral of the story. DO NOT bridge the neutral earth on the inverter output permanently. Use a relay to perform this function when in islanding mode only.

Thanks for the assistance this morning Isetech. Much appreciated. And so we learn.

I would hazard a guess and say you are going to be back there for a mains incoming neutral fault - Could be that there is a loose connection coming into the property and that every now and then it utilizes the inverter neutral due to the bonding

[Derlyn]

You are probably right GCE.

I'll wait for them to phone and tell me that they're getting a tingle on the shower taps.
That's my bad neutral signal.

[Isetech]

or flickering lights.

You are probably right GCE.

I'll wait for them to phone and tell me that they're getting a tingle on the shower taps.
That's my bad neutral signal.

[Isetech]

The more I scratch this neutral/earth bond the more it itches.

Too many things popping up which are neutral/earth bonding related issues.

I hope it is not going to take a person getting electrocuted for the powers that be stand up and sort it out once and for all.

I am willing to step up and join a group of people with a lot of elctrical experience to sit down with a bunch of meters and technical skills and try figure out how to create a safe environment for the public. I can make time on a Saturday morning and my time will be free.

Herholdts has a decent service centre in Durban with all the equipment needed to test and test some more. It would be even better if Sunsynk stepped up and showed their commitment to resolving this issues which negatively effects their equipment, because of the open relay which is not fail safe. They have the capacity to make their units safe in SA.

[Isetech]

What would we be trying to achieve:

1/ To find a way to make the relay fail safe, by using a N/C contact, which would have to be linked to the inverter control and display a fault, and message to the app. This is the only method you can use in eThekwini.

2/ To identify if the permanent bond is dangerous, why there is a high current on the bond and if it poses a danger to the the public and animals or if it is just circulating current within the system. THERE SHOULD NEVER BE A A CURRENT ON AN EARTH WIRE, UNDER NORMAL OPERATING CONDITIONS EVER. If you think I am talking crap, connect an earth leakage unit and tell me what happens.

3/ To identify which earth arrangement requires a permanent bond or a rely, as we are all aware, you cannot by law do a permanent bond on on an inverter with a TN-S system, which is the earthing arrangement in eThekwini. I cannot comment on other parts of the country. This also why it is so important for people to start doing a little research s that they know what system arrangement is applicable for their area.

[GCE]

There was a crowd that sat around a table and had the discussion that is how this article came about

https://ecasa.co.za/technical/neutral-earth-bonding-clarified/

Same way that there was a +/-6hr zoom meeting on Friday last week to get various manufacturers and others around a table for discussion over batteries with the view of putting out some sort of guidance which may still take awhile

[Isetech]

Either way it cant be that dangerous, otherwise the sale of these units would be halted, warning labels would be required exposing the dangers and there would be court cases.

Bottom line, just do what you think is right because at the end of the day it is not up to the electrician or installer to make the regulations.

Make sure whichever method you use, have the support of that group.

Has anyone done any tests with a meter ?

[Dylboy]

Only thing I have seen, is I had a perm neutral earth bond on the output of the inverter, I this time as a test put and inline 15Amp fuse in that perm bridge.

Went back the next day and that fuse had popped.... When I measured current at that time I was getting 9Amps when the grid was available, when the inverter went into island mode I had 0amps on the perm bond...

Sent from my CPH2197 using Tapatalk

[Justloadit]

Only thing I have seen, is I had a perm neutral earth bond on the output of the inverter, I this time as a test put and inline 15Amp fuse in that perm bridge.

Went back the next day and that fuse had popped.... When I measured current at that time I was getting 9Amps when the grid was available, when the inverter went into island mode I had 0amps on the perm bond...

Sent from my CPH2197 using Tapatalk

There should be no permanent Neutral/Earth bond on the output of the inverter if in Hybrid mode, or pass through mode, as the incoming supply would have this connection done at the transformer point.
Only when the inverter changes to Islanding mode should the Earth/Neutral bond take place, as the inverter now becomes the supply source, and for proper ELU operation, the Earth/Neutral bond now takes over.

[Dylboy]

Yes 100%, it was an install of someone else which had tripping issues and saw the perm neutral earth bond in which I did some tests on, i did then add a contactor to make and break.

Still was an interesting test and it came about a post from Isetech awhile back when he measured current on the earth so thought it would be a good test, it was quite awhile ago.

Sent from my CPH2197 using Tapatalk

[Derlyn]

I would hazard a guess and say you are going to be back there for a mains incoming neutral fault - Could be that there is a loose connection coming into the property and that every now and then it utilizes the inverter neutral due to the bonding

@ GCE. You are a foretune teller supreme.

Was called back on Friday for no mains power.
Main breaker faulty. ( Replaced )
After carefull inspection I noticed the telltale brownish burn mark on the neutral side of breaker.

I can only assume that the breaker was on it's way out and that there was a high impedance across the neutral contact inside.