Neutral/earth bond for inverters

[Isetech]

As per a discussion today, what you need to understand is that the inverter is not an "online" system, it switches over from grid (at this point you cannot have a dual neutral/earth bond) to UPS (islanding mode) which is disconnected from the grid power, the reason the relay is used. For Sunsynk inverters it has a preset delay before the supply is reconnected, which is the reason it must NOT be connected directly to the mains, but rather through the contact in the inverter.

An inverter is like a cheap UPS, the grid power goes in and the grid power comes out, only when the inverter goes into islanding mode is the mains disconnected and from the mains and the DC power is converted to Ac power.

Until someone can draw a picture that doesnt show a double neutral/earth bridge on the system while the power is in grid mode, I will be connecting all the relays already installed on all the installations I have already completed. All future installation will have a relay.

This is a challenge to everyone installing inverters, what is creating the high leakage currents on installation which have a permanent bond and how dangerous is this high current.

If you do inverter installations you dont even need a leakage current detector to identify this high current, just clamp any clamp meter.

[Isetech]

My only concern is public safety, lets get this right.

[Isetech]

Another concern I have is the municipality bridging the neutral and earth at the pole(TN-S) , without fitting a label on the meter so that when an inspector is doing a COC see that the system has been modified from a TN-S to a TN-C-S. But that is a whole different thread on its own.

[Dylboy]

That is hectic ! That means break down of insulation or something so that the current is taking the Earth.

Now with this Info how do we correctly size the bridge wire ?

My thinking is that in island mode and the bridge is made that insulation is still bad and current using the E to get back to Neutral. So surely we must use bridge wire of that CSA of the phase.

I need to find time and draw some of this out properly.

Most homes I have seen there is a bridge of N and E at supplier. Very good E loop readings.

That bridge should carry Earth fault current but now when we talk of broken/stollen/missing neutrals on the main feeds then it gets interesting with lots of high currents flowing which ever way to get back to the TX.

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[Derlyn]

On a standby generator installation, is the changeover switch the point of control ?

[Isetech]

The bridge for the generator doesn't affect the mains, it is only used when the changeover switch is in generator mode, if you bridge the neutral/earth at the output of the generator "CHANGEOVER" switch, you then create a second neutral/earth bond, which according to the code is non compliant. Any inspector worth his salt will switch off the installation because having 9 amps flowing in the earth wire would be regarded as dangerous, right ?

This would be a good example, if you fitted the bridge at the output of the change over switch you would be doing the same thing as the permanent bond on the inverter (the auto changeover switch is built into the inverter).

The bypass switch (some would call it a changeover) installed in a DB next to the inverter is NOT the changeover switch. It is a bypass switch used when the inverter requires maintenance or is damaged and has to be removed for repairs. It is a safe way to keep the power on for the essential supply.

I have noticed people are clueless with the wiring of this section of the system. You cannot feed the inverter from the bottom of the double pole isolator which feeds the "bypass" switch, once you get this right it will help you understand what all the fuss is about.

Using the N/C of the relay as a fail safe for the bridge and the N/O for the LED, this should be added to the regs, unless someone can come up with a better idea.

Just remember I am referring to TN-S system earthing, which is how our municipality is suppose to provide our power. Your location might have a different system earth.

Which is why I believe it should be law that a label is fitted to the outside of the meter box and when the municipality decide to modify the supply the label should be updated. In fact it should have a label at all the DB's to prevent any confusion.

On a standby generator installation, is the changeover switch the point of control ?

[Isetech]

By the way I also identified my leakage current on the lighting circuit while doing these tests. it wasn't the 9 amp, but rather 198mA (0.2 amps), which explain why it trips the ELU.

Would 0.2 amps leakage current on the neutral fail an insulation resistance test, I thought seeing that everyone is in think mode, this might be a another brain teaser for some

Why I ask the question, if you are doing a test report and the people are living on the property at the time of the test or there is sensitive electronic equipment on site which could go band as soon as you connect and start pushing 500 or 1000 V to test the insulation resistance.

[Derlyn]

On a standby generator installation, is the change over switch the point of control ?

[Isetech]

Just something to add, I dont believe a double pole breaker is going to solve the problem.

While doing these tests I found that the current on the red was between 1-2 amps, the current on the red was between 2-3 amps and the current on the bridge was between 5-7 amps. The riddle is where is this high current coming from and how dangerous is it ?

We all know that there will always be leakage current, in fact its normal for devices to have leakage current, does this current pose a danger to the humans and animals etc, and if so at what point and how can we prevent it, that's the real question?

[Justloadit]

Just something to add, I dont believe a double pole breaker is going to solve the problem.

While doing these tests I found that the current on the red was between 1-2 amps, the current on the red was between 2-3 amps and the current on the bridge was between 5-7 amps. The riddle is where is this high current coming from and how dangerous is it ?

We all know that there will always be leakage current, in fact its normal for devices to have leakage current, does this current pose a danger to the humans and animals etc, and if so at what point and how can we prevent it, that's the real question?

The question should rather be, what is causing this current?
Is it from the load, or is it from the source?
If the load is is the case, then there is something incorrectly wired and not using the Neutral as a return.
If from the source there could be missing Neutrals/Earths from the sub station line to the property under test.

[Isetech]

As soon as I switch the mains off to the inverter, everything is "normal" all the readings are within spec.

If I remove the bridge with the power off, the voltage L-N = 230 VAC, L-E = 80 VAC and E-N = 120 VAC (roughly), what I expect to see.

If you go to any inverter which has a "permanent" neutral/earth bond and clamp a standard current clamp meter onto the bridge wire while the grid power is switched on, you will see this current fluctuating.

The only reason for my concern is what happened on the weekend while testing an inverter. Getting wacked like that on an earth wire got my attention.

The question should rather be, what is causing this current?
Is it from the load, or is it from the source?
If the load is is the case, then there is something incorrectly wired and not using the Neutral as a return.
If from the source there could be missing Neutrals/Earths from the sub station line to the property under test.

[GCE]

The question should rather be, what is causing this current?
Is it from the load, or is it from the source?
If the load is is the case, then there is something incorrectly wired and not using the Neutral as a return.
If from the source there could be missing Neutrals/Earths from the sub station line to the property under test.

From Load - There will always be slight leak to earth from stoves , geysers , any element will generally leak to earth - Light fitting ballasts even electronic have slight leaks

On source - Unless the phases are balanced 100% there will be current from the star point ( neutral) to earth - In my opinion when you have a better earth neutral bridge on your premises you could end up with some of the incoming imbalance from the street trying to earth itself on your star point

[Isetech]

Could it be that the inverter electronics are creating this high current because it is grounded, when it shouldn't be?

If you switch off the mains the current is gone, switch on the mains its back.

It will be interesting to see what happens if I disconnect the neutral/earth bond while the unit is connected to mains and clamp the meter on the supply earth and the UPS (output) earth.

[GCE]

when you switch mains are you switching neutral as well ?

If you are , trying switching off live only - If you still get current then it could be from street

[Dylboy]

I clamped a bridge wire today and had 2.9Amps.

This was with Grid on and all working normally.

This 2.9A is very scary.

I don't know if it is the installation using E as a bit of a return or the street council thing. The inverter is a Deye 8kw. I didn't install it. But the earth leakage tripa randomly when power goes so that is why I have the bridge to test. Limited time to be there so small steps.

Back to the 2.9amps... is it the supply side of inverter, is it the street or is it the installation such as a light circuit having a N and E touching.

My understanding of PME is it's good and used in a TNC-S system. Having this bridge on the load side of the inverter is where it's tricky for me as j feel it's a supply and thus not caring about the grid but it appares to be an additional PME as the inverter works with the grid and matches frequency etc.




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