Anyone with knowledge of the TT electrical networks used in France and Japan?

[kolek]

Sorry for this wall of text, I tried to keep this short but it's not easy.

There are other ways to handle electrical system grounding (aka earthing), and other countries do it differently from the United States.

France and Japan use a "TT" type electrical systems which:

- do not bond anything to any current carrying conductor at the service
- do not pose any serious risks in the case of a broken neutral
- should always have an RCD (GFCI) as its first isolator

See https://en.wikipedia.org/wiki/Earthing_system for more info about the TT electrical system.

My electrical panel:
- Has 3 wires, L1/L2/N, 3 phase 100/200VAC
- Does not have a neutral busbar
- Does not have a ground busbar
- Has no option to bond neutral to ground
- Has an RCD (GFCI) protecting all the house breakers
- Has neutral being switched on/off by the main breaker and the RCD

Current earth ground / neutral / bonding situation:
- No earth ground connected to the panel
- Only have an earth ground where the washing machine is located, but unclear if that is actually connected to earth
- No grounding wire or 3-prong plug at the outlets, with the exception of where the washing machine is located.
----

Doing research on others installing solar in Japan:
- Cannot find anyone discussing N-G bonding, whether that happens here, or if it's necessary here

Already spoken about this with others on the forum here in Japan, like @Daddy_Tanuki. And unfortunately the electricians in Japan are unfamiliar with DIY solar and aren't qualified to handle an install like this.

Unlike most U.S. solar installations, you can install small residential solar in Japan without permits or inspections.

Details about my system:
1 x DEYE SUN-8K-SG01LP1-US/EU, 8KW, 48VDC IN, 100/200VAC IN, 100/200V OUT
28 x LONGI SOLAR HALF-CUT LR4-72HPH-455M, (455W) MODULES
28 x (EVE) LiFePo4 BATTERIES, 3.2V, 280AH, JKBMS TOTAL 28.672kWh, 51.2VDC

My plan is to:
1. Install a RCD (GFCI) at the inverter input, and there is already another RCD installed at the output, so that all house circuits are protected by the RCD

2. Run a ground wire to the panel and connect that to inverter chassis ground as well as other metal cases in my install.

3. Run a ground wire from the PV panel frames to the inverter chassis. (better to connect PV frame ground to inverter rather than directly to grounding rod according to @Hedges)

I'm including a picture of my electrical panel.

But beyond those 3 things, anyone have any other suggestions? I'm particularly unclear about how to handle the N-G bond in a TT electrical network like Japan. Please do NOT comment if you have no knowledge of an electrical environment like this. Patronizing or hysterical comments like "GET HELP BEFORE YOU START A FIRE AND ELECTROCUTE YOURSELF" will be ignored.

Thanks guys!

 

[crossy]

Your first port of call should be the book of words for your inverter, I'm assuming you came up dry there

A TT system doesn't have a N-G bond at the customer, the N is grounded at the transformer and nowhere else.

When running off-grid you need to simulate that source N earth so that your RCD/RCBO functions correctly. But that link needs to go away when running on-grid.

I believe the Deye has a N-E relay so you could connect the E of the off-grid output to a local rod and all would be good.

 

[Bop]

TT is very rare, and is not exactly easy to deal with... (and people with experience with it equally rare)

It also relies entirely on active circuit protection for safety (RCDs- which are quite reliable, but not 100%, which is why most places don't allow it...) rather than more passive protection
The French system is the only one I have had any experience with and little at that...

It is incorrect to say TT has no neutral/earth bonding (in fact that is what the first T stands for- the neutral and earth are bonded, just at the source only, the second T means the end load has its own separate earthing system independent of the grid supply system)- so there is indeed a N/E bond, just it is done at the power source only, and replies entirely on the entire circuit remaining intact and fault free from the source to the use point- a dubious assumption in many cases...
It also can have issues as it relies entirely on having a good LOCAL earth point- not always a safe assumption.... (poor ground conductivity can lead to possible dangerous voltage levels, with the potential for a shock even with RCDs in place)

Any TT system should have RCDs that break BOTH the Active/Line conductor AND the neutral conductor (not always the case, so check that yours are of the correct type- all RCDs MONITOR both conductors, but many only break the Active/Line conductor) and should be regularly tested, both for correct operation of the RCD breaker (pressing the 'test' button at the recommended intervals), and for good earth conductivity for the local earth point/s...

That it poses no risks in the case of a broken neutral is incorrect, a broken neutral conductor can still be 'pulled high' through a low resistance load that is switched on after the fault location, and an RCD will not detect this and shut down- leaving BOTH the active and neutral 'live' downstream of the fault location...

Another thing to be aware of is a RCD device and a RCCB device are NOT interchangeable- an RCD can be damaged and fail to operate correctly if the current exceeds its output current rating and requires a separate MCB to provide over-current protection, where an RCCB does not (it has both functions built into the one unit...)- again check exactly what you are getting to see if it is suitable!!!

As your inverter operating in stand alone mode is the sole current SOURCE when islanding, I would suspect it has to be N/E bonded at the inverter itself when in island mode, and have its own ground/earth source as well (only someone familiar with the Japanese regs would be able to say for certain is this is a legal requirement or not...) but that would be my understanding of it and how I would do it... (after checking the actual regulations of course...)

 

[kolek]

Your first port of call should be the book of words for your inverter, I'm assuming you came up dry there

Right the Deye manual isn't specific to TT

A TT system doesn't have a N-G bond at the customer, the N is grounded at the transformer and nowhere else.

Ok that is very useful to understand.

I believe the Deye has a N-E relay so you could connect the E of the off-grid output to a local rod and all would be good.

Can we first define offgrid in this case?

Like most here, the inverter will be connected to the grid, unless there is a blackout/loss of service. When the batteries are charged, we will run from batteries, when the batteries are empty we will be running from grid.

So this is a "ongrid" or "grid-tied" and the term "off-grid" does not apply.
However, are you defining "off-grid" to be whenever the inverter is running from battery?

 

[kolek]

That it poses no risks in the case of a broken neutral is incorrect,

Wikipedia says [TT] "does not pose any serious risks in the case of a broken neutral." If that information on Wikipedia is wrong you might request the editors to change it.

It is incorrect to say TT has no neutral/earth bonding

Can you please show where in my post it says TT has no neutral/earth bonding? The closest I came to saying that is [TT] "does not bond anything to any current carrying conductor at the service" which is straight from TT references on Wikipedia.


I'm still digesting the rest of your remarks. Thanks for your input!

 

[kolek]

RCD can be damaged and fail to operate correctly if the current exceeds its output current rating and requires a separate MCB to provide over-current protection, where an RCCB does not

So you recommend a RCCB over a RCD in a TT environment?

 

[timselectric]

Bob , covered everything well.
I'll just point out that L1,L2,N is not 3-phase.
It's split-phase, but I think that they just call it single phase in Japan.

 

[crossy]

This diagram is probably your best bet.



With no PE from the grid itself the Grid-PE connection would be your local ground rod.

When the grid is down the N-PE relay closes grounding the N on the Load output allowing your RCD/RCBOs to operate correctly.

 

[Bop]

Wikipedia says [TT] "does not pose any serious risks in the case of a broken neutral." If that information on Wikipedia is wrong you might request the editors to change it.


Can you please show where in my post it says TT has no neutral/earth bonding? The closest I came to saying that is [TT] "does not bond anything to any current carrying conductor at the service" which is straight from TT references on Wikipedia.


I'm still digesting the rest of your remarks. Thanks for your input!

Many take the wiki article to mean TT presents no risk at all with a broken neutral- however this is incorrect- TT is exactly the same as any other supply configuration in regards to a broken neutral (and in some respects could be considered MORE of a risk in certain circumstances than some other configurations)- the exact risk level depends on the particular form of fault involved.... it can be less- but not always...

I covered that only a few sentences earlier- TT has no N/E bond- other than at the SUPPLY...
Usually the supply is the grid...

HOWEVER- when your inverter is running in island mode (which IS 'offgrid' even though it is normally connected to the grid, in island mode it is exactly that- an 'island' isolated from the grid) it is now the actual SOURCE, and now must provide the N/E bond...

Some jurisdictions are OK with having secondary N/E links downstream, some are not (France definitely doesn't like them, but Australia, which uses a 'modified TT' called MEN (multiple earth neutral) it is legally required!!!
MEN is kinda a mix of several different types, closer to TNC-S probably than a pure TT system, but really not the same as any of the other more widely used versions- with multiple N/E links along the entire distribution system, from the source to the final one at the fusebox/distribution board...


What the Japanese regulations are, I am unsure of, but I know France doesn't like secondary neutral bonds- mostly... lol... (except when they do it anyway...French wiring can be 'interesting' lol) but they do require a N/E bond at the SOURCE (be that the grid, a generator or an inverter operating in island mode) but nowhere else...

This can be difficult to achieve with many 'hybrid' inverters as that bond at the inverter has to be open when operating in gridtie mode, and closed when islanding... something many can't do with their stock configurations (some do it by manually removing a screw or link- but very few have the ability to do it automatically) one of the joys of using a not very common distribution system, as adding extra 'options' that cost extra to implement, and aren't required in most places anyway- well they get left out to shave the manufacturing costs down...

 

[kolek]

Island mode means when the battery is charged and the inverter has switched to running from DC power?

 

[Bop]

Island mode means when the battery is charged and the inverter has switched to running from DC power?

Correct (sorta) hence the name... it has become an 'island' of power in the overall grid- neither importing nor exporting power (something that is frowned upon in all jurisdictions- when there is a blackout- NO exports of any kind, all wiring basically 'disconnected' completely to prevent accidental backfeeding in fault conditions...)

They all seem to dislike line workers getting killed when repairing faults on a supposedly 'dead' line for some strange reason...
;-)
When running in gridtie mode, it still is connected to the mains, although exporting if the loads are less than the PV array production, importing if it is less- regardless of the state of charge of the battery...
Island mode is 'emergency generator mode' ie there is a blackout... no export or imports at all...

 

[timselectric]

When the inverter disconnects from the grid, it also disconnects from its N/G bond. So, it must provide its own.

 

[kolek]

As I understand it, the Deye / Sunsync inverter has a relay that can automatically activate the N-E bond when the grid is switched off (which would only happen if I switched off the grid connection or there was a blackout). However, it probably cannot activate the N-E bond every time the inverter switches from running off the grid to running from battery.

@houseofancients your thoughts on this?

 

[timselectric]

As I understand it, the Deye inverter has a relay that can automatically activate the N-E bond when the grid is switched off

Correct
Its usually a common pole on the relay, that switches between incoming neutral and bonding. So that both are never connected at the same time.

 

[kolek]

If the inverter cannot activate the N-E bond every time it switches to battery and I have to choose between either no N-E bond when running in island mode, or persistant hardwired N-E bond in both modes, I've read it safer to run with a persistant hardwired N-E bond.

 

[Bop]

If the inverter cannot activate the N-E bond every time it switches to battery and I have to choose between either no N-E bond or persistant hardwired N-E bond, I've read it safer to run with a persistant hardwired N-E bond.

That depends entirely on the local regulations- in France at least, auxiliary N/E bonds are frowned upon, and they may not allow connection to the grid at all if they are present- what Japans stance on this is I have no idea...

 

[kolek]

That depends entirely on the local regulations- in France at least, auxiliary N/E bonds are frowned upon, and they may not allow connection to the grid at all if they are present- what Japans stance on this is I have no idea...

I've spent a couple hours researching it and cannot find any information in Japanese about N/E bonding. I have not found a Japanese solar video or document even mentioning it.

 

[timselectric]

If the inverter cannot activate the N-E bond every time it switches to battery and I have to choose between either no N-E bond when running in island mode

You are mixing two different things.
It can run from battery without disconnecting (physically) from the grid.
In this case it's still using the grids bond.
It only needs to create it's own bond, when it disconnects from the grids bond.

 

[kolek]

You are mixing two different things.
It can run from battery without disconnecting (physically) from the grid.
In this case it's still using the grids bond.
It only needs to create it's own bond, when it disconnects from the grids bond.

Ok, if that's the case then the solution is simple, just using the inverter's built-in bonding relay, right?

@Hedges (if I understood him correctly) was saying that the inverter was an island that needed to supply a N/E bond when it switched to running from battery.

 

[timselectric]

Ok, if that's the case then the solution is simple, just using the inverter's built-in bonding relay, right?

Correct