MultiPlus-II 48/5000/70-50 + Pramac EPW3000 floating neutral generator. Correct N-PE bonding?

DIY
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1

Hello,

I have an off-grid installation with:

- Victron MultiPlus-II 48/5000/70-50

- 48V battery bank (~15kWh)

- 5.5kWp PV

- TT earthing system with earth rod

For generator backup I currently use an old three-phase generator connected directly to the AC input of the MultiPlus.

I also own a Pramac EPW3000 Electric Start generator (230V single phase, AVR, 2.7kW rated output), but it has never been connected because my electrician identified it as a floating-neutral generator and was concerned about the earthing arrangement and RCD operation.

According to the Pramac manual:

“The mid-point (neutral) conductor of this equipment is not grounded.”

The manual also states that when supplying a facility in a TT network and where residual current protection is required, a 30mA residual current device must be installed and the generator frame must be connected to earth.

My questions are:

1. Is a floating-neutral generator such as the EPW3000 compatible with the AC input of a MultiPlus-II 48/5000/70-50 in an off-grid TT installation?

2. What is the recommended Victron-compliant arrangement for neutral-earth bonding when the generator is connected?

3. Should the N-PE bond be provided by the generator side, by the installation, or by a dedicated switching arrangement?

4. Is there any specific Victron documentation or Wiring Unlimited section that covers this exact scenario?

At the moment the generator has never been tested with the MultiPlus, so I don’t know whether the issue is a real incompatibility or simply an installation/earthing concern. The electrician, seeing that it had floating-neutral, decided to use the old generator (Where neutral and earth were connected). But It has less power (in a single phase), worse frequency control, and basically is worse in all senses, so I am still trying to use the newer one (Which we bought for our previous inverter, which used an external charger for the 24V batteries)

Thanks in advance.

P.S.: I have seen some post about this, like Inverter generator on Multiplus AC IN - DIY - Victron Community ot Generator hook up to Multiplus 2 10kva, floating neutral question - DIY - Victron Community but not sure about what is usually prefered here, so I opted for opening a new thread.

2

Do you have pictures from the wiring board or the manual??

3

I can post photos of the manual if you want something in particular, if you prefer the full one, it is in Pramac - EPW 3000 Electric start

In particular, the part about the ground is:

image
image663×286 49.8 KB

4

Where exactly is the N-PE connection done? If its done in the main switchboard, after the MP, then you are fine with using a generator with isolated Neutral.

If you are relying on the internal N-PE relay of the MP, then as soon as an AC source is connected, that AC source is then responsible for the N-PE connection. If that source is a genset with an isolated Neutral, then also the rest of the system will be isolated to PE, and RCDs wont work properly.

Grounding the generator frame does not help, since thats not the generator star point.

If you are permanently off grid, then personally i would use a permanent N-PE connection in the main switchboard instead of either the MP or the genset.

5

Talk to your local sparky!! He has to do some measurements on site before connecting the genset for safety!! To drive an earth rod in the ground and connect without measurements ist suicidal (if there is too much resistance)!!

The manufacturer says also for safety reasons use a RCB with 30mA trigger point ( but which type?? Btw., in case of an inverter generator some guys want to plant an B Type!!) directly near the genset. If the generator is in a shed, it should mounted near the entrance (emergency stop from outside the shed!)

Since your genset is AVR i would talk with the local expert for the suitable protection (RCBO A-Type). maybe your “grid input” allows a normal mounting (L-N separate from GND, Grounding in the grid input junction box and so directly at your hut-grounding system)