Neutral/earth bond for inverters

[Isetech]

I have installed and setup a couple of Sunsynk units. There are still a few things I need to learn about them.

The challenge is that all 3 are linked in the unit and they use relays to control them.

Line in (grid)
Aux/Generator
UPS (output)

[Thys LOW Elektries]

I have installed and setup a couple of Sunsynk units. There are still a few things I need to learn about them.

The challenge is that all 3 are linked in the unit and they use relays to control them.

Line in (grid)
Aux/Generator
UPS (output)

A number of training videos available on this subject. The Line in (grid) is also the line out for feedback to the grid and power for non-essential loads. This is what the ct and ct ratio is all about All I can say it was higher grade solar install the first time I watch it after it all made sense it was easy peacy

[Isetech]

Due to uncertainty I have just been doing a permanent neutral/earth bond, on the Axpert and Sunsynk units, fortunately I have already installed the relays with a 6 amp mcb on all the sites. If the manufacturer recommends you use a relay, you should use a relay, throw in a few interesting tests carried out, its time to go back to all the sites and connect the relays.

There should be warning labels on all all DB's on installations with permanent earth/neutral bonds.

I believe there should be a test result added to the (COC) test report, the current flowing in the neutral/earth bridge wire.

[Isetech]

We have an interesting situation in part of the world, the good old TN-C system which use to be the way things were done.

It seems someone realised they could save a lot of time and money and just bridge the neutral earth at the pole. If you log a high loop impedance fault, they will arrive within 48 hours and bridge the neutral earth at the boundary of your property.

What happens if the council do this, well your elctrical system is no longer a TN-S but instead a TN-C. A notification should be sent to the customer who should contact the electrical contractor so that they can update the (COC) test report and a noticed fitted to the meter box and at the main DB.

If you testing a property and your loop impedance test result is as low as 0.3 ohms, chances are someone has already bridged the neutral earth, throw in a permanent bond on the property (creating a second neutral/earth bond) no problem, until you start having insulation resistance issues between phases and earth.

Which then takes us to the next question, is it safe to install an earth spike on a property which has a TN-C system.

Can the council just convert your system from a TN-C to a TN-S without any a notification or at least a notice on the meter box.

Thank goodness non of this stuff poses any danger to the customer or user who is responsible for the electrical installation

[Dylboy]

My question is that Earth bond, will it not have to carry fault current ? Thus being same CSA of the phase ?

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[Dylboy]

By fault current if there is a Line and E touch in the installation, that current will flow down the E and the Bond wire to the Neutral and then while this is happening being of a high current ti trip the CB.

I am not sure what surge high current a 2.5mm or 4mm cable can carry as I use a 4mm for my bridges either via contactor or perm wire.

Also what would happen if I use an inline fuse on the perm wire, you will know fuse gas blown as then the earth leakage will trip next to every single time

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[Isetech]

This might turn into an interesting thread, after spending a whole day fault finding on an electrical installation with a permanent (double) neutral/earth bond. The test result were rather interesting.

My question is that Earth bond, will it not have to carry fault current ? Thus being same CSA of the phase ?

Sent from my CPH2197 using Tapatalk

[Isetech]

Another interesting observation, the wire used for the bonding between components and the main earth.

You go to all this trouble, earthing and bonding the system and then connect the earth wire in the 4 core surfix, OK.

It wouldnt be a bad idea installing a separate earth wire suitable for the earthing and bonding.

[Isetech]

What happens if all my earthing and bonding is done to code, wire sizes correct and secure and we have a leakage current live to earth on a light circuit for example or a sub DB or even the input to the inverter of around 1 amps, the current will just keep going round and round and nothing will happen, right?

What happens if you are working on a sub DB and you disconnect all the earth wires and leave them loose, what would be the potential difference be between the loose earth wires?

Would an appliance become a potential hazard if it lost the earth connections?

[Isetech]

Its going to be an interesting day today, lots of tests to be done.

The site is suppose to be TN-S system earthing, what I have recently discovered is that if the L-E loop impedance is below 0.4 ohms, there is going to be a good chance that there is either a neutral/earth bond on the pole outside the property (become common practise by the utility) or inside the property if the value is really low.

I know for a fact there is a low insulation resistance issue on the lighting circuit (even though the property has a COC, issued recently).

The big test is going to be the current flowing in the neutral/earth bridge. I want to see if this high leakage current is common on other sites with a permanent neutral/earth bond. I also want to see what the open circuit potential difference is L-E, L-N and E-N.

If electricians are connecting the neutral to earth on the property while the inverter is not in islanding mode, why not just connect the neutral and earth at the main DB and the sub DB and everywhere you might get a high loop impedance reading?

[MarkN]

Due to uncertainty I have just been doing a permanent neutral/earth bond, on the Axpert and Sunsynk units, fortunately I have already installed the relays with a 6 amp mcb on all the sites. If the manufacturer recommends you use a relay, you should use a relay, throw in a few interesting tests carried out, its time to go back to all the sites and connect the relays.

There should be warning labels on all all DB's on installations with permanent earth/neutral bonds.

I believe there should be a test result added to the (COC) test report, the current flowing in the neutral/earth bridge wire.

I use a green indicator lamp and place important test notice on all DBs with a contactor based E/N bond, that it must be tested/verified to be on (green indicator) when on backup power. This is similar to the tests required by the home user to ensure RCDs are working (RCD test button) and SPDs are still functional (SPD indicator).

[Derlyn]

Neutral earth bond may not be on the load side of the main isolator, so doing it on a sub db is a no no.

As an aside, here in East London, specifically Mdantsane, the Municipality does NOT supply a seperate earth conductor to houses. I cannot remember when last I got an earth loop impedance reading of more than 0,3 ohms. The earth neutral bridge is done in the prepaid meter on the pole outside.

[Isetech]

Only recently has our the municipality started doing this on the pole outside.

Neutral earth bond may not be on the load side of the main isolator, so doing it on a sub db is a no no.

As an aside, here in East London, specifically Mdantsane, the Municipality does NOT supply a seperate earth conductor to houses. I cannot remember when last I got an earth loop impedance reading of more than 0,3 ohms. The earth neutral bridge is done in the prepaid meter on the pole outside.

[Isetech]

The tests carried out today confirm that it is extremely dangerous to do a permanent bond on an inverter when not in islanding mode, there were currents of over 9 amps (you dont even need leakage current clamp) on the bridge wire.

What is very more concerning is that an AIA member has threatened court action against me if I dont do a permanent bond, but rather do what is recommended by the manufacturer, install a relay.

Anyone else done a test on the bridge wire, you gonna shyte yourself when you see the currents flowing in the bridge and earth. What ever you do, do remove the earth wires while the system is on, otherwise you gonna experience a nasty little bite like I did on the weekend.

Any wiring configuration that electrocutes you if the earth wires are not connected is reason enough for concern.

Anyone else tried these tests or feel my comments not correct?

Please feel free to jump in anytime and set the record straight.

I am just going on the test results I see at the AC changeover panel and they are deeply concerning.

[GCE]

Agree with you - on a TN-S system your neutral earth bridge ( star point) is going to be better then the utilities star point so definitely the house will rather earth through your newly created star point . My issue is that you could become the star point for the street and on a 500Kva transformer you could easily end up with 80Amps flowing through .
In discussions I have had I say that if the AIA's think that is the way then the protection on the inverter supply needs to be a double pole circuit breaker ( not SPN) so that the neutral can trip if the current goes up.

I honestly do not see the utilities allowing it to happen which is why clause 6.1.6 was introduced - The AIA argue that you have a new point of control and I say that the definitions do not allow an inverter to be a point of control which is supplied by a supplier
Besides 7.16.4.6 which to me is pretty clear


6.1.6 The neutral conductor shall not be connected direct to earth or to the
earth continuity conductor on the load side of the point of control except as
allowed in 7.16.4

7.16.4.6 A TN-S system shall not be converted to a TN-C system

3.56
point of control
point at which a consumer can, on or in any premises, switch off the electrical
installation from the electricity supplied from the point of supply

3.58
point of supply
point at which a supplier supplies electricity to any premises

3.77
supplier
in relation to a particular installation, any local authority (see 3.47), statutory
body or person who supplies, contracts or agrees to supply, electricity to that
electrical installation