Neutral earth bonding on backup systems.

[GCE]

Why is everyone referring to an inverter as a generator and not a UPS? It looks like a UPS, it has batteries like a UPS, it converts DC to AC like a UPS, It even has the same output voltage reading as a UPS, it has a display like a UPS, it must be a UPS.

If it looks like .... , it smells like .... it must be ....

It is easier to describe as a generator being fitted into the regulations and the fact that you normally have to check earth neutral bond , 4 pole switches , sync with mains , and it converts one form of energy into electricity , on a PV inverter anyway.

UPS is pretty standard fit into the installations due to the design

[Isetech]

The way I see it, in a normal domestic installation you should never have the generator connected to he mains while the grid connected. The inverters on the other hand are connected together with the grid and only when in islanding mode will it be disconnected/isolated from the grid.

When you connect a generator, it has mechanical interlocks which can be manually or automatically switched, but should never be connected at any point, hence the break before make contacts.

This is where I believe the confusion arises, when the grid and inverter are operating together, we were taught (right or wrong, that we can discuss another time) that you never bond the neutral/earth after the "point of supply" or at 2 points in an electrical TN-S installations.

While your essential supply (output of the inverter) is connected to the grid, there should never be a bond between neutral and earth.

The only time there should be a bond between neutral and earth is when the inverter is in islanding mode (disconnected from the TN-S system) at which point you create a TN-C before the essential DB, (output from the inverter) , at the essential DB, you would then create a TN-S system and at not point after the DB, should the neutral earth be bonded again.

[Isetech]

I believe the confusion is also created by annex P, P1 clearly indicating that all neutrals must be bonded to together and clearly indicating a completely separate unit, with a a combined a neutral/earth bond at the star point of the generator and an earth spike (another discussion for another discussion for another day)

However if you look at P3 which I see as representing an inverter, but is is not that simple because P1 is 3 phase and P3 is single phase and compared to a UPS would be feeding dedicated socket outlets which dont require earth leakage protection.

I wish more people would get involved in these discussion, because I believe it is very important to understand theses topics, rather than just follow the herd.

Just imagine a court case, with so many different opinions. If you could show evidence that you have looked at all the discussion on this topic, it would be difficult for anyone to prove that you have been negligent.

Something else you need to consider, you could argue that the manufacturer suggests the use of a relay, some might argue that you need to comply with the SANS regs, but if this discussion is taking place and the responses are so random, how do you decide.

I would suggest that someone with the right connections, contact the people who are responsible for the electrical industry, the DOL and request an official statement to clear up the confusion.

I am not saying anyone is anyone is right or wrong, my concern is the confusion around this topic.

I dont think we need to be too concerned because if either option was dangerous, something would have been done about it by now.

[Isetech]

J.1 System earthing identification code
The first letter of the identification code denotes the relationship of the source of energy
to earth:

T one or more parts are connected direct to earth; or

I all live parts are isolated from earth or one point is connected to earth through
impedance.
The second letter of the identification code denotes the relationship of the exposed
conductive parts of the consumer's installation to earth:
T the exposed conductive parts of the consumer's electrical installation are
connected direct to earth, independently of the earthing of any point of the source
of energy; or

N the exposed conductive parts of the consumer's electrical installation are
connected direct to the source earth, which, in the case of an a.c. system, is usually
the transformer neutral point.
The designation TN is further subdivided depending on the arrangement of the neutral
and protective conductors. A further letter or letters denotes such arrangement, as
follows:

C the neutral and protective functions on the incoming supply and in the consumer's
electrical installation are combined in a single conductor;

S the neutral and protective functions on the incoming supply and in the consumer's
electrical installation are provided by separate conductors; and

C-S the neutral and protective functions on the incoming supply are combined in a
single conductor

[GrahamH]

The way I see it, in a normal domestic installation you should never have the generator connected to he mains while the grid connected. The inverters on the other hand are connected together with the grid and only when in islanding mode will it be disconnected/isolated from the grid.

When you connect a generator, it has mechanical interlocks which can be manually or automatically switched, but should never be connected at any point, hence the break before make contacts.

This is where I believe the confusion arises, when the grid and inverter are operating together, we were taught (right or wrong, that we can discuss another time) that you never bond the neutral/earth after the "point of supply" or at 2 points in an electrical TN-S installations.

While your essential supply (output of the inverter) is connected to the grid, there should never be a bond between neutral and earth.

The only time there should be a bond between neutral and earth is when the inverter is in islanding mode (disconnected from the TN-S system) at which point you create a TN-C before the essential DB, (output from the inverter) , at the essential DB, you would then create a TN-S system and at not point after the DB, should the neutral earth be bonded again.

I completely agree with what you are saying, but I'm confused... I have a newly installed Deye 8KW inverter which is working just fine, however, the installation was not done exactly as per the User Guide which says that for South Africa, the neutral must be linked to Earth at the main board which is contrary to what I learnt many years ago. I can imagine many safety risks when there is more than one earth to neutral link along with any uncertainty regarding the quality of my own "local" earth. IE, any significant voltage difference between the incoming neutral from Eskom and "real" earth might cause my earthed devices not to be safe. (Hope I'm making sense)

The sample diagram for South Africa in the User Guide also shows that the inverter input and output neutrals are effectively connected together which prevents the output from floating when the grid is off of course. I have tried bridging them and it works fine. If the incoming neutral is connected to earth at the eskom transformer, then bridging the in and out neutrals removes the need to link earth to the output neutral?

[Isetech]

Dont worry there are a lot of people questioning these diagrams.

I completely agree with what you are saying, but I'm confused... I have a newly installed Deye 8KW inverter which is working just fine, however, the installation was not done exactly as per the User Guide which says that for South Africa, the neutral must be linked to Earth at the main board which is contrary to what I learnt many years ago. I can imagine many safety risks when there is more than one earth to neutral link along with any uncertainty regarding the quality of my own "local" earth. IE, any significant voltage difference between the incoming neutral from Eskom and "real" earth might cause my earthed devices not to be safe. (Hope I'm making sense)

The sample diagram for South Africa in the User Guide also shows that the inverter input and output neutrals are effectively connected together which prevents the output from floating when the grid is off of course. I have tried bridging them and it works fine. If the incoming neutral is connected to earth at the eskom transformer, then bridging the in and out neutrals removes the need to link earth to the output neutral?

[Derlyn]

Do a simple test using your plug tester.

With Eskom off and your inverter on, use your plug tester and make sure the earth leakage trips on either 20, 25 or 30mA.

If it does, what are you worried about ?

[GrahamH]

Dont worry there are a lot of people questions these diagrams.

Thanks, I think I now understand what I need to do. The inverter has an advanced option called "Signal island mode" which outputs 220v on its ATS connector. The 220v turns on the moment the grid is disconnected and turns off 60 seconds after the grid is turned on again IE when the inverter connects to it. That tells me I need to operate a contactor with a N/O contact to make the Neutral to Earth connection only when the inverter is in island mode. The :hager ESC227 would probably be the best option.

[GrahamH]

Do a simple test using your plug tester.

With Eskom off and your inverter on, use your plug tester and make sure the earth leakage trips on either 20, 25 or 30mA.

If it does, what are you worried about ?

Thanks, it does trip. My concern really is about getting a C.O.C. for the installation. (warranty, insurance etc.)

[Isetech]

Some manufacturers seem to feel the relay is the way to go and as GCE also pointed out, he agrees, will it affect your warranty, well that we will have to wait and see.

What is the correct solution, personally I agree with the relay, it makes sense, however I have my concerns as pointed out by many others, what happens if the relay fails, Victron are were you would expect, way ahead of the crowd, they have built in relays and fail safe measures, Sunsynk do have so units with built in relays, however they dont have fail safe protection which will result in a VOV situation, then you have the external relay option which also has no fail safe measures, using the N/C to fail into the closed position have been options mentioned. Axpert, well you get what you pay.

Then you have real UPS devices, which in the past have never required a neutral/earth bond, in most cases being connected to dedicated socket outlets.

Thanks, it does trip. My concern really is about getting a C.O.C. for the installation. (warranty, insurance etc.)