Neutral earth bonding on backup systems.

[Isetech]

Why is the neutral/earth bond so important.

Are we more concerned about the safety of the home owner or the electrician working on the grid supply.

IF we permanently the earth/neutral, you create parallel paths, with that come a few challenges.

One of them being that if you connect the neutral earth you now have a TN-C type situation while the grid is connected to the inverter (not islanding mode). Yes we do understand that the inverter is not an appliance and shouldnt be treated as such.

J.2.5 TN-C system earthing


All exposed conductive parts of a consumer's installation are connected to the PEN
conductor as indicated in figure J.2.5.


NOTE This system is not allowed, because this part of SANS 10142 stipulates that a separate
earth and neutral be run to each appliance beyond the point of supply. The loss of the PEN
conductor can result in the appliance's becoming live and earth leakage protection might not
operate. This system is not approved for use in a.c. installations in South Africa. If such a system
is identified, it should be converted to a prescribed system in consultation with the supply authority.


If you fit a relay and it fails, the backup unit should have some form of protection to shut down the system because it will create a VOV situation, which means you end up with an elevated neutral earth voltage, well over 25 VAC. A simple solution is to install a voltage monitor after the relay and if the voltage exceeds a safe limit the unit will shutdown. At the same time make sure there is also protection against creating a TN-C system.


Something to think about: As pointed out by someone, the equipment should be sold with all the safety devices built in. What happened to SABS approval?

5.4 Characteristics

5.4.1 General
The characteristics of the selected equipment shall be appropriate to the
conditions and parameters on which the design of an installation is based.

That comment, with your qualifications, you should know better and that grey area. This topic has certainly identified another huge problem in the elctrical industry.

The question the end users is asking, how dangerous are these backup system installed on my property? What is the DOL doing about it?

If the installers cant even agree on the earth/neutral bonding, what about the lithium battery that was installed in kitchen against a single brick wall or next to the back door and there is no other fire escape route, because as we all know in SA our windows are sealed closed with strong metal frames. You could always just use a bucket of water to out out the flames DONT.

[Isetech]

How you read this part of the regulations pasted below, could be where all the confusion originates.

This example in P1 would represent a larger generator or alternate supply from a large device, not a little 5 kva unit installed in your garage.

For example if you had a 15 KVA generator or 16 kva inverter or bigger (depending on the supply) connected at the meter (point of supply), P1 would apply.

Installing a 5/8/12 KVA standby system doesnt apply if the supply is 60 amps or above, why, because you can only connect the neutral and earth together at the point of supply. The inverter is not the point of supply while the unit is connected to the grid, it only becomes the point of supply once it switches to islanding mode.

How can you resolve this challenge for smaller standby units with built in changeover/islanding relays, simple the unit should be supplied with a built in relay with suitable devices to isolate the unit if the relay fails and or the voltage exceeds the touch voltage as per the regs.


7.12.3.1.2 In an installation that is supplied from a combination of
transformers and alternative supplies located near to each other, the neutral
points of each of these items shall be connected to a single earthed neutral
bar (see P.1 and figure P.1). This earthed neutral bar shall be the only point
at which the neutral of the installation is earthed. Any earth leakage device
shall be positioned in such a way as to avoid incorrect operation due to the
existence of any parallel neutral/earth path.

[Dylboy]

How you read this part of the regulations pasted below, could be where all the confusion originates.

This example in P1 would represent a larger generator or alternate supply from a large device, not a little 5 kva unit installed in your garage.

For example if you had a 15 KVA generator or 16 kva inverter or bigger (depending on the supply) connected at the meter (point of supply), P1 would apply.

Installing a 5/8/12 KVA standby system doesnt apply if the supply is 60 amps or above, why, because you can only connect the neutral and earth together at the point of supply. The inverter is not the point of supply while the unit is connected to the grid, it only becomes the point of supply once it switches to islanding mode.

How can you resolve this challenge for smaller standby units with built in changeover/islanding relays, simple the unit should be supplied with a built in relay with suitable devices to isolate the unit if the relay fails and or the voltage exceeds the touch voltage as per the regs.


7.12.3.1.2 In an installation that is supplied from a combination of
transformers and alternative supplies located near to each other, the neutral
points of each of these items shall be connected to a single earthed neutral
bar (see P.1 and figure P.1). This earthed neutral bar shall be the only point
at which the neutral of the installation is earthed. Any earth leakage device
shall be positioned in such a way as to avoid incorrect operation due to the
existence of any parallel neutral/earth path.

If the N bars are joined but grid goes down and we lose the N E bond then we would still need a relay surly ?
This is on about the last bit in this message.

I don't have much time but I'm keen to chat more on all this.

Off to my little ones first concert haha.

Sent from my CPH2197 using Tapatalk

[Isetech]

Not if the standby system is connected at the point of supply, for example a 16 KVA unit connected to a 60 amp supply.

When you install a 5 kva unit, it cannot be connected at the point of supply, because it doesnt have the capacity to carry 60 amp and therefore cannot be connected at the point of supply. As we are aware you convert a TN-S into a TN-C after the point of supply. Once the inverter switching into islanding mode, the relay will bridge the neutral and earth creating a TN-C supply at the standby unit and feed into the essential supply which is a TN-S system. The system is described as a TN-C-S system.

That is how I understand it, I am not an electrical engineer and encourage anyone who knows better to correct these statements if they are incorrect.

If the N bars are joined but grid goes down and we lose the N E bond then we would still need a relay surly ?
This is on about the last bit in this message.

I don't have much time but I'm keen to chat more on all this.

Off to my little ones first concert haha.

Sent from my CPH2197 using Tapatalk

[Isetech]

I have 3 concerns with the attached diagram:

1/ A 5 kva standby unit cannot be connected directly to the point of supply.

2/ Some of the standby units have a common earth, they dont have LNE as terminal, only LN and common earth plate, so the note " Do not connect this terminal when the neutral wire and PE wire are connected together" cannot apply, It seems that someone just copied what they thought was the correct way to do it.

3/ Using single pole breakers in a single phase system.

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?

[GrahamH]

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.

On the point of warranty... I purchased the Deye 8 kW along with a mounting panel which already had the inverter and the wiring installed. The panel had a 32 amp breaker on the output of the inverter. 32a x 230v = 7.35 kW which is well below the inverter's rating. The User Guide for the inverter specifies the maximum CONTINUOUS pass through current at 50 Amps and proposes that the output breaker should be 63 Amps. (Like double what the installed breaker is) I raised this with the supplier who simply said that the if the breaker is more than 32 Amps then they will not honour the warranty. They also sell a pre-assembled version of the Deye 5 kW inverter which also has the same breaker. I pointed out that this makes no sense, but they stuck to their guns.

I also attended a presentation on installing the LuxPower 5 kW inverter and the presenter said that the input breaker should be no more than 25 Amps, whereas the manual for the device clearly specifies 63 Amps. I pointed this out to the presenter who also said that they would not honour the warranty if the breaker was more than 25 Amps.

I was a hardware engineer for a large computer company for many years. There was no way that the documented specifications were open to interpretation.

[Dave A]

I raised this with the supplier who simply said that the if the breaker is more than 32 Amps then they will not honour the warranty. They also sell a pre-assembled version of the Deye 5 kW inverter which also has the same breaker. I pointed out that this makes no sense, but they stuck to their guns.

I also attended a presentation on installing the LuxPower 5 kW inverter and the presenter said that the input breaker should be no more than 25 Amps, whereas the manual for the device clearly specifies 63 Amps. I pointed this out to the presenter who also said that they would not honour the warranty if the breaker was more than 25 Amps.

I believe some of the local distributors are chancing their arm; jumping at any excuse to remove the risk of having to deal with a warranty claim. I saw one distributor peddling the Growatt 5kW SPF5000 inverter with 3.6 kWh Dyness batteries as a bundle, with a disclaimer that if you only installed two of the batteries, the warranties were invalidated on both the inverter and the batteries if the BMS ever went into overload protection. I can tell you that when you register the product with the manufacturers, there is no such fine print in place. And when I queried this with my supplier, they said it was nonsense too.

[GCE]

How you read this part of the regulations pasted below, could be where all the confusion originates.

This example in P1 would represent a larger generator or alternate supply from a large device, not a little 5 kva unit installed in your garage.

For example if you had a 15 KVA generator or 16 kva inverter or bigger (depending on the supply) connected at the meter (point of supply), P1 would apply.

A BIG NO - YOU CANNOT USE P1

Annex P is informative and is to help understand the written regulation . Looking at P1 while reading the regs
7.16.4.6 A TN-S system shall not be converted to a TN-C system.

Basically
If you own the minisub then you are earthing the neutral and have access to the star point to connect your genset to that point .
If you don't own the minisub you will not have access to it and then need to ensure that you do not earth the neutral again which is where the 4 pole change over comes in.
If your generator is to far from he minisub that you own then you will also not earth the neutral permanently - you will use a 4 pole switch.

Before jumping between inverters and generators along with what should be allowed into the country first fully understand the regulations around generators then it is easy to talk on inverter neutral earth bonding.

I have had the argument with consultants in shopping centers - Because the store they are doing within the shopping center is a 500KVA supply with a 500KVA genset taking the stores full load they seem to think that they do not need to install a 4 pole switch - I point out reg 7.16.4.6 and then disconnect them in the sub station until a 4 pole switch is installed - I have been taken on by lots of consultants and always hear the same story , In Cape Town/Joburg/ Durban it is not a problem - My question - Who gives you the authority to take my TN-S supply and make it a TN-C supply ?
The 4 pole switch gets installed.

You quote 7.12.3.1.2 which does not apply to your scenario so you need to continue to 7.12.3.1.3

7.12.3.1.3 Where alternative supplies are installed remotely from the
installation, or from one another, and where it is not possible to make use of
a single neutral bar or neutral conductor which is earthed, the neutral of each
unit shall be earthed at the unit and these points shall be bonded to the
consumer's earth terminal (see 6.12.4). The supply from each unit which
supplies the installation or part of the installation, shall be switched by means
of a switch that breaks all live conductors operating substantially together
(see figures P.2 and P.4), to disconnect the earthed neutral point from the
installation neutral when the alternative supply is not connected (see also
6.1.6).
NOTE Where four pole switching is implemented, consideration should be given to use
overlapping neutral switching devices.

The biggest confusion comes from looking at the pictures without reading what is actually wanted and then use the picture for clarity

[GCE]

I have 3 concerns with the attached diagram:

1/ A 5 kva standby unit cannot be connected directly to the point of supply.

2/ Some of the standby units have a common earth, they dont have LNE as terminal, only LN and common earth plate, so the note " Do not connect this terminal when the neutral wire and PE wire are connected together" cannot apply, It seems that someone just copied what they thought was the correct way to do it.

3/ Using single pole breakers in a single phase system.

The drawing clearly states - Please follow local wiring regulations

The majority of inverters etc are coming in from Asian countries where translation to English is generally a problem
How many times have you taken a instruction manual for a time switch and thrown it away because it made no sense and sent you in the wrong direction while trying to set it up ? Same problem with inverter manuals

[GCE]

In short to this thread

The Neutral earth bond must be present at all times to ensure that protection operates correctly and within time - You sign as such on your test report for Mains and test report for Alternative supply.(8.6.1)

You cannot change a TN-S system to TN-C system - This is why you use a 4 pole or 2 pole change over on a generator and why you use a relay/contactor on an inverter.

What is confusing about that.