Neutral earth bonding

[Tradie]

I know this is a sticky topic, but in reality it is an extremely important topic.

What have we learnt in the past 3 years.

1/ Understand the type of earthing arrangement.
2/ A permanent neutral/earth bond is not the best solution, in fact as we know having 2 neutral earth bond on one supply is a really bad idea, especially on TN-S systems.
3/ An external relay is also not a smart idea, especially if the bond is made after the changeover switch.
4/ There a big difference between a changeover switch and a bypass switch, understanding where and why it is used is extremely important, especially when dealing with neutral/earth bonding.
5/ Built in (inverter or gateway/changeover panel) neutral/earth bonding on the UPS/inverter/essential input is the key to a safer installation.

This topic should be discussed in a lot more details, considering time delays on certain inverters, especially if an external relay is switched by via a terminal provided in side an inverter.

I am going to say it again, this is not a pissing contest and I encourage people at any level in the electrical/solar industry to share your input, because everyday we keep learning and the only way to improve the safety for our customers is by open discussions.

[Tradie]

There is a Sunsynk video out going into a bit of detail about Sunsynk inverters and how they work.

The way he explains it in the video, there is no changeover switch inside the inverter, but rather a gris contact which is opens, when it goes into islanding mode.

The grid power, Inverter and Aux are all connected to a single bus, when it goes into islanding mode the contact from the grid opens, and the other 2 stays closed ( depending on how the aux is configured)

The way I understand this, the neutral earth must never be permanently bonded because the grid and inverter power is on the same bus (creating a double neutral earth bond in the same installation).

If a generator is connected, there is not need to neutral earth bond the generator, because the neutral earth bond relay will do the bonding on the inverter (UPS) side once the grid is dropped.

Now I have more questions than answers,

1/ Switching time for the relay, when the inverter drops the grid and switching time when the grid is reconnected.

2/ Built in safety to shut down the inverter if the relay fails or you loose the neutral earth due to damaged cabling etc.

3/ What will happen to all the installations with a permanent bond?

4/ Class 1 and class II devices, as discussed on this platform, if the inverter is a class II device, why would you bond the generator before the inverter, both being class II devices, connecting a generator with a neutral/earth bond, would that not create and double neutral earth bond, like the permanent bond?

5/ Should there be a specific relay with time delays or switching rates ?

6/ If Sunsynk have a zero switching rate then why do the light flicker when the grid relay makes and breaks, he did explain that it depends on the charge or discharge state.

It looks like the only reason for the video, was because the bottom line is being affected by the the new kid on the block, who are pushing for the top spot. Which one is better, it is hard to tell without an apples for apples comparison.

[Tradie]

The single line diagrams create more concerns, hopefully they use double pole contacts inside the inverter to to break the grid supply, when going into Islanding mode. If not we have an even bigger problem.

The fact that the AC is on a single busbar makes the whole neutral earthing challenge even more important.

[Tradie]

A question: If half the industry believe their way of doing something is the correct way and the other half believe it should be done another way, where do you draw the line and get the person responsible for the electrical industry to stand up and correct the challenges before someone gets hurt or killed ?

[GCE]

The neutral earth bond issue is str forward with regards to the regs . No bond after point of control.

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.

I have heard that some municipalities insist on a visible permanent bond , not sure if it is still like that .

I have heard the argument of the time between disconnect and reconnect of the earth or relay failure - all valid , but how do we prevent stolen neutral earth bonds in sub stations , ELU failures , Breakers welded on contacts due to previous fault and not picked up - All goes down to maintenance in the end.

I have seen what happens when a permanent earth bond with 6sqmm wire is done and the star point in the sub is stolen or comes loose . The 6sqmm wire looks like a heater element taking the sub station of 800kva imbalance down to earth.

And that could happen with a relay . We install D/pole circuit breakers ( not SPN) before inverters so that if there happens to be a case where the neutral tries to earth through the inverters star point the breaker should trip and prevent the 6sqmm wire from being a heater element

[Tradie]

I think the double pole is a good idea, the SPN (commonly referred to as a geyser combo).

Star point in an inverter", I assume you would be referring to a low frequency 3 phase inverter?

We install D/pole circuit breakers ( not SPN) before inverters so that if there happens to be a case where the neutral tries to earth through the inverters star point the breaker should trip and prevent the 6sqmm wire from being a heater element