For a MultiPlus-II 48/5000 in a European off-grid installation with an earth rod and a portable inverter generator with floating/symmetrical output on AC-in: should the generator provide the N-PE bond, or is the internal ground relay expected to maintain RCD protection during pass-through?
Yes, since as soon as the MP switches over to ACin, its internal N-PE relay will switch off. Therefore, as long as the generator, or whatever power source is connected to ACin, is available and switched through, this source is also responsible for grounding the neutral.
If the generator does not provide an N-PE connection, then either the source is rejected by the MP (If theres is a voltage difference between N and PE) or if its not rejected and switched through, then the connected RCDs on the ACout wont work.
You can provide your own solid N-PE connection for example in the main switchboard, but then you should deactivate the MPs internal N-PE relay, as well as making sure any generator that gets connected also has a floating Neutral. Otherwise you would have more than one N-PE bond which should be avoided (or is even against electrical code depending on the region).
Thanks for your quick answer. Seems like there are different opinions on this. I for example found the below post. Are there any best practice on how to do this?
Having a floating and a grounded biphase output are two different things.
I personally have never seen a biphase output generator, with a grounded coil center, but surely possible. I would expect an inverter generator to produce a floating output.
Im not fully there, since a floating output can just as well be at the same 50% voltage level. For example due to common mode capacitors on the output.
Thats true, since all the RCD needs is that bond to ground, whether its a biphase output with grounded coil center, or a “true” neutral with a bond to ground doesnt matter.
But the main point is “ground referenced”. If the output is biphase with a grounded coil center, then adding an external N-PE connection will short circuit one half of the generator coil, which would trip the generators output breaker.
Also correct, but thats one of the main reasons that some electrical code does not allow for more than one output socket on a floating source (and prohibits the use of power strips on it). So you can only plug a single device in and still be safe without an RCD.
I guess this is the main point here. Check what type your generator is, if its output is floating or not, and if it can be grounded externally.
Yes, many. And the deeper you go into grounding the worse it gets.
But generally, the main differences are described as TN and IT networks.
Your local electrical code decides whether you need an N-PE connection or not. But be prepared to stumble into a lot of if’s and when’s as well as “it depends on the situation”. Sometimes theres no clear cut answer even from the code, so you have to decide on a system to use.
The key part is that you take that decision and stick with a system, rather than having an undefined situation where the inverter still uses its N-PE relay but the generator produces a floating output, effectivly switching systems with the ACin switching.
So the thread you quoted in this question was raised by me originally.
In the end I fitted a simple E-N grounded plug in the spare generator plug socket and everything worked well. I used a socket tester in the house sockets and they all passed so must assume it did what I wanted (keep the RCDs operational)
I used Google AI very deeply to go over and over this before I went ahead. It helped a lot and I checked it’s referencing for it’s supplied info.
Thank you! I am surprised that this is not more commonly mentioned in wiring schematics and such. This scenario must be very common.
I do however of course understand that there are many ifs and buts but seems like many just don’t care as long as it works.
I have one follow-up question.
My installation will never be connected to the public grid. It is a standalone off-grid cabin with:
MultiPlus-II 48/5000
Earth rod
RCBO-protected AC output
One portable inverter generator (Einhell TC-IG 2000) connected via a CEE inlet.
Instead of a permanent N-PE bond in the main switchboard, would it be acceptable to create the N-PE bond at the generator connection (for example in the CEE inlet box or a dedicated generator adapter), so that the bond only exists when the generator is connected?
What are the advantages and disadvantages compared to:
Permanent N-PE bond in the main switchboard with the MP ground relay disabled.
N-PE bond only at the generator connection with the MP ground relay enabled.
Is one solution preferred by Victron (or the community), and if so, why?
You can do that, and the inverter will provide the ground link when the generator is off. I did once try to provide a ground with a link on the inverter AC in - like you I’m completely off grid - but the generator had an insulation fault and could not cope with the external ground.
I’m now running 2 x PM2 3k in parallel, with a 3rd PM3k as a dc charger (Cheaper than the equivalent iSkylla charger) and don’t have to worry about the generator grounding issue. Using the extra MP for a charger allows the AC current to be controlled, and allows maximum peak free loading of the generator, improving efficiency and reducing run time.