Neutral earth bonding on backup systems.

[Isetech]

It seems there little confusion amongst electricians with regards to when you should do neutral earth bonding and when you shouldn't, types of earthing systems and which are used and when.

Some say you have to permanently bond an inverter and others believe a relay must be used to prevent circulating currents and other.

Some cant tell the difference between a generator and a UPS and wiring configuration required for each.

A generator doesn't have an internal changeover switch so an external changeover over switch is required. It all by law doesn't require islanding mode, but does require mechanical isolation to prevent both supplies running together.

An inverter/UPS on the other hand is different beast, with all sorts of complex electronics, bi-directional flow on the input, a built in changeover switch and required by law to go into islanding mode when the grid power switches off.

What are your thought on earth neutral bonding for a generator and a UPS, is it the same thing?

Do you feel a relay should be used to bond the neutral/earth or permanently bonded on the output of the inverter.

Do you feel the SANS regs adequately cover this topic.

But most important do you understand the different earthing systems feeding the property and why you actually require a neutral/earth.

When a neutral/earth bond is dangerous.

What are the implications of neutral earth bonding on the property if the earthing system a TN-S

Can you go from a TN-C to a TN-C-S to a TN-S all in one elctrical installation.

Who thought this could become so complicated, add a bidirectional hybrid inverter with a generator and a few solar panels and boy do we have a mix.

[Dylboy]

100% this is not covered enough and also not at all.

There are a lot of things I agree. TN-C-S can be dangerous, so knowing if yo use a relay or permanent bond is important, also will it ever change.

With inverters is it an appliance so bonding the output permanent will it matter ?

There is so so much to learn and to try and learn is very difficult.

Not enough training of what matters as most who install don't even know what the Earth is for other than a draw wire...

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[GCE]

With inverters is it an appliance so bonding the output permanent will it matter ?

There is so so much to learn and to try and learn is very difficult.

Not enough training of what matters as most who install don't even know what the Earth is for other than a draw wire...

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We are listening to too much noise being create by so called Solar experts that have never studied or worked in the electrical industry , picked up scraps and trying to make it sound like there are no regulations so they can continue without abiding by any rules .

An inverter is not an appliance . ( That is solar talk for I don't have to be an electrical contractor or issue a COC to install an inverter.)

An inverter is " electrical equipment " as per definition in SANS 10142-1

3.32
electrical equipment
item or any combination of items, including wireways, which is used for the
generation, conversion (such as of voltage or frequency), transmission or
distribution of electrical energy

and is part of the electrical installation as per definition 3.33 and definition 3.16

3.33
electrical installation
machinery, in or on any premises, that is used for the transmission of electrical
energy from a point of control (see 3.56) to a point of consumption
(see 3.55) anywhere on the premises, including any article that forms part of
such an installation, irrespective of whether or not it is part of the electrical
circuit, but excluding

3.16
consumer
person who is supplied (or who is to be supplied) with electricity by a supplier
(see 3.77); or a person who supplies his own electricity


Now if you now start thinking electrical and check regulations for Electrical the rest becomes str forward .

An inverter is treated the same way as a generator - 7.12

7.12 Alternative supplies
NOTE Alternative supplies include but are not limited to low-voltage generating sets,
photovoltaic (PV) installations, gas generators, diesel generators, wind turbines and
hydropower plant.

Reset the mind- forget all the Solar talk noise from people who are trying to convince themselves and clients , that it is not electrical.

[GCE]

The earthing

When a generator is connected to an installation and you running off mains you may not earth the neutral ( 6.1.6 ) - when mains fails and the generator supplies power you must earth the neutral - This is why you use a D/pole change over or 4 Pole change over

Same story with an inverter - The mains is fed directly to the output during mains on - When mains fails then the relay switches and you feed power from the Inverter/Battery side of the relay .
Some units automatically bridge neutral earth others you need to do the bridge .
To find out if it has an automatic bridge , carry out loop test , if the readings are crappy then it does not have and you need to make a plan .
On a generator you would open the terminal box on the genset and install a bridge wire . On an inverter you would need to open the unit trace the circuits , find the relay and install a bridge on the correct side of the relay. Electricians fingers are to big to work inside those little boxes and warranties could become a problem along with grid tie circuits so it is easier to just install a relay/contactor on the output of the inverter that will do the bridging where our big fingers can work in peace.
If the inverter has an output to operate that relay , easy , if not then use the mains to power the relay and when mains falls away the bridge between earth and neutral happens through the relay/contactor.

I have had one of my guys get that confused look with a relay until you explain it is a light switch , just has burst of power to change the state of it , not a finger.

If you think it is not covered in the regulations then look at 7.16.4
When Mains fails then the inverter becomes the supply and you need to ensure that it passes the tests

Remember that a test report needs to be done for mains supply and for alternative supply when it is on .

If you listen to solar talk - They say tick alternate supply , job finished - A BIG NO - Tick alternative supply then another test report needs to be attached to the COC ( 8.6.1)

The regulations are there , they explain most of what needs to be explained just don't get confused with Solar talk


8.6.1 General
NOTE Conduct all tests and complete a copy of the test report for each distribution
board and supply (normal and alternative supplies). Amdt 1


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 Neutral earthing
7.16.4.1 Whereas TN-C systems may be implemented along the distribution
system backbone, the individual service connections at every distribution
kiosk shall be TN-S.
7.16.4.2 From the point of supply to each user or part of a communal
installation, the neutral and earth conductors shall be separate conductors.
7.16.4.3 Wherever the neutral is connected to the earth, a warning notice
shall be fitted to the outside of each distribution kiosk in the distribution
system, indicating "Neutral earthed inside".
7.16.4.4 A clear notice shall be fitted at the combined neutral-earth
connection inside each distribution kiosk in the distribution system, that
prohibits the removal of this connection while the supply is alive, or might
become alive.
7.16.4.5 The neutral shall not be earthed beyond any earth leakage unit.
7.16.4.6 A TN-S system shall not be converted to a TN-C system.

[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]

Didn't you do PV training?

100% this is not covered enough and also not at all.

There are a lot of things I agree. TN-C-S can be dangerous, so knowing if yo use a relay or permanent bond is important, also will it ever change.

With inverters is it an appliance so bonding the output permanent will it matter ?

There is so so much to learn and to try and learn is very difficult.

Not enough training of what matters as most who install don't even know what the Earth is for other than a draw wire...

Sent from my CPH2197 using Tapatalk

[Dylboy]

Didn't you do PV training?

No not yet, still want to but not yet, mostly I want to sit with the tech people at the big inverter companies and really learn the inner workings of each one. Each inverter has its proprietary things and knowing that will help a lot.

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[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.

[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?