Neutral/earth bond for inverters

[Derlyn]

This is not how it works.
Effectively if you take your Clamp tester, and test Live current, it should read exactly the same if you measure the Neutral current. Now if you take a very sensitive clamp tester, and place Live and Neutral through your clamp meter, there should be zero Amps because the two currents will cancel each other out. Now if there is a small current flowing either from Live or Neutral to Earth, provided there is a bond connection before your measurement point, there will be an imbalance in the current flowing Through Neutral and Live, and you clamp meter if sensitive enough would measure this imbalance. The ELU works the same way, but the imbalance causes the breaker to trip. If there is no Earth Neutral Bond before your clamp or before the ELU, then there will be no imbalance, as there will be no current flowing from Live and Neutral to earth, as there is no return path, and therefor will not trip.

Here is a video which explains it with pictures.

You can do a Google search for other videos which goes deeper into the theory

Thanks, Brother. Watched the attached video 3 times. Bit difficult to understand the " chinese " English.
I understand 100% how an earth leakaqe relay works. In my previous posts I said that it detects a difference in the currents flowing in the live and neutral conductors and shuts off the supply should there be a difference of 30mA or more.

That is exactly how it works.

I also gave you a good example of an earth leakage relay tripping when there is no current ( ZERO ) flowing to earth.
In fact, the test button on the unit doesn't even cause a current to flow to earth. It creates a bypass current, much the same as my lights scenario, which causes the currents in the 2 coils to differ, thus tripping the unit.

I think most confusion comes from the name " earth leakage relay". This name implies that the unit only trips if there is a leakage current to earth and that it references earth. It does not and cannot do so without having a physical connection to earth. Us, from the old school, call it an earth leakage relay, but it seems as if the new terminology is RCCB ( residual current circuit breaker ) a much better name.

When the unit senses an imbalance in currents through the live and neutral, it does not know what is causing the imbalance. Most people assume that it's a current flowing to earth, but it needn't be. It could be flowing to anywhere.

I am yet to be convinced that the unit references earth.

[Justloadit]

I am yet to be convinced that the unit references earth.

If there is no earth connection, then any connection after the RCCB to earth will not trip, because there is no current flow to earth. You practically could connect Live to earth, and the unit will not trip, because "Live" is a term we just gave this wire, it is live with reference to the other wire, but not Live to earth, as there is no earth reference.

It is the same as connecting a V-0-V generator to your DB via the change over switch. Once it runs on the generator, then the RCCB will not trip if any of the V-0-V lines are shorted to earth. If you connected the centre of the V-0-V to earth, then the RCCB would trip, as there is a path to earth from the Live wires via the centre connection. However if there is a Earth/Neutral bridge on the DB, and you are using the V-0-V, then the RCCB will work, however if you have connected the centre of the V-0-V to earth, you will short the winding out and damage the generator.

[Justloadit]

I think most confusion comes from the name " earth leakage relay". This name implies that the unit only trips if there is a leakage current to earth and that it references earth. It does not and cannot do so without having a physical connection to earth. Us, from the old school, call it an earth leakage relay, but it seems as if the new terminology is RCCB ( residual current circuit breaker ) a much better name.

When the unit senses an imbalance in currents through the live and neutral, it does not know what is causing the imbalance. Most people assume that it's a current flowing to earth, but it needn't be. It could be flowing to anywhere.

I am yet to be convinced that the unit references earth.

One of the issues I have noted from the videos and articles which attempt to explain the inner workings of the ELU or RCCB units, is that they 'assume' that the specific site is properly grounded(Earthed), and so the explanation does have merit. However they do not mention anything about if there is a bad earth.

This is one of the reasons of the COC is to do the earth loop test. This is to ensure that there is proper earthing, in order that the ELU/RCCB units will function in the case of an earth fault.

Here is an explanation by an electrician which may shed more light

Paul Richards
Electrician at Royhill

And speaking from practical experience. First time I was asked to install a RCD on a generator I suspected it required a MEN. Boss said no. Test button worked fine. I went and got the RCD tester and no won’t trip. Looked into the requirements and spoke with an inspector to confirm. An MEN connection is required on the generator side of the RCD to operate correctly.
In order to detect the inballance an earth reference point is required. Now on a cheap centre tapped generator with 110–0–110Vac where the 0 is connected to E you cannot install a MEN as you will short one winding. But the RCD will probably work. But in Western Australia ( and probably all Australia) this sort of Generator would most likely be illegal to sell. Other countries allow these.
In a situation fed from an electricity grid it would probably still work as there are multiple earths from the supply transformer to all the other buildings attached. So if yours at your premises wasn’t connected the RCD should work fine.

[Dave A]

Without the earth-neutral bridge, there is no path to complete the circuit with a fault to earth.
So there is no current.

Also, the single point that is bridging the circuit to earth (the fault) becomes the voltage reference point for that point in the circuit.
Which is why a safety supply is "safe".

[Isetech]

Something else to consider which most people dont understand, by using a neutral earth bond, it actually changes the class of the inverter or generator.

[Isetech]

By the way at this point there is no right and wrong (a lot of confusion), but what is important is that people need to share their view. The more these topics are discussed the more the industry will improve.

I am slowly learning that it does help running out and pointing fingers at eaveryone who might not agree with your view on a topic or your understanding on a regulation.

Should you use a realy or should you use a permantant bond, at this point, it doesnt really matter. I am yet to see a court case over a neutral bond, for now its all just hot air. Nobody has died yet as a result of the either so we will have to be a little patient.

[Isetech]

It seems one of my customers has decided to open a can of woorms, the good thing about it is that it is going to make me pay attention and get it right. It's time to prepare the documentations for the challenges I will soon be facing . This would be a good place for me to reference the information.

The first question is do I need a relay for the bond or do I just do a permanant bond.

We have to get the facts right from the start.

The installation is a 60 amp single phase TN-S supply

Where we live, no earth spikes are required, just like the fact that all domestic dwellings are rated to 2.5 ka (since I last checked, about 10 years ago) from the supplier.

Do we factor in theft when deciding the bond method, or do we just stick to the facts.

Copy and paste from the latest SANS regs.

Note it is important you understand your local system earthing.


7.12.3.1 Neutral bar earthing
7.12.3.1.1 Protection in accordance with the requirements of 6.7 shall be
provided for the electrical installation in such a manner as to ensure correct
operation of the protection devices, irrespective of the source of supply or
combination of sources of supply. Operation of the protection devices shall
not rely upon the connection to the earthed point of the main supply when the
generator is operated as a switched alternative to the main supply.
Where there is no existing earth electrode installed in the electrical installation,
a suitable earth electrode may be installed in accordance with SANS 10199.
When installed, the electrode shall be bonded to the consumer's earth terminal
and to the earthing point on the alternate supply by a conductor of at least half
the cross-section of that of the phase conductor, but not less than 6 mm2
copper, or equivalent. This also applies to a single-phase supply
(see also 5.2.3.1).


NOTE 1 In a TN system earthing of electricity supply, an earth electrode is normally
not required in an electrical installation.


NOTE 2 Protection of photovoltaics can be by means of or surge protective device
(SPD).

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).


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.


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.

6.12.4 Earthing of the neutral of combined sources
When an installation that has a common neutral is supplied from a
combination of transformers and generators located near one another, the
neutral terminal of each of these items shall be connected to a single neutral
bar. This neutral bar shall be the only point at which the neutral of the
installation is connected to the consumer's earth terminal except as in the case
in 7.12.3.1.3 or 7.16.4.

[Isetech]

While we are about it, I also need to clear up the earth spike confusion.

Surge protection and lightning are not the same thing.

Just because you install surge protection in the DB, it doesnt mean the building has lightning protection.

[Isetech]

Just like clamping a earth wire onto a metal object doesn't mean the entire structure is earthed or bonded.

You need to measure the earth continuity at various points on the structure

[GCE]

It seems one of my customers has decided to open a can of woorms, the good thing about it is that it is going to make me pay attention and get it right. It's time to prepare the documentations for the challenges I will soon be facing . This would be a good place for me to reference the information.

.

What is the can of worms he is wanting to open - Just over neutral earth bridge ?

[Isetech]

Not just neutral/earth bridge, trust me its complicated.

What is the can of worms he is wanting to open - Just over neutral earth bridge ?