I have one system running this set up and all is good, no problems. However I am just reviewing the AC wiring as I have not quite followed the data sheet.
The 4 pole breaker and RCD doesn’t make a lot of sense, if it protects circuits towards the MP2 then as soon as the N-E link closes it will trip. I however think it points towards the Loads and Generator / grid (RCCB usually in at the top, out at the bottom). And again as soon at the grid contactor closes the RCD will trip due to the N-E link at the DNO cutout.
Any thoughts on this, I have been going around in circles?
Hello Simon, I would say that the current path towards the MP no longer exists when relay C opens, so there is no residual current at the RCD. In island mode, there is also only one N–PE connection, since N is disconnected from the grid.
The RCD works in both directions.
It will not, because the N–PE connection at the Multi opens again and the “star point” at the Multis is no longer earthed.
Even a generator in the consumer installation would not trip the RCD if the current flowed towards the battery in island mode, since here too the star point of a generator is not earthed.
Thus, there is always only the path via N; under no circumstances (except in the event of a fault) does a second current path via PE back to the generator arise.
It’s more about protecting people. I have an RCD on mine, a 20m run from the switchboard to the garage. As an example, if a rat chewed the cable, it would trip, but if there were a circuit breaker, unlikely you would see a fault, and the system would continue to run. It never trips when operating normally. The relay is open when there is power on the input, and when it loses power makes its own EN connection.
This is an example application circuit for qualified installers and cannot be transferred on a one-to-one basis to every installation.
You can’t see anything here for the generator because generators normally have their own protection when connected by plug. If permanently installed, this is handled by a qualified professional.
As mentioned above, the Mp correspondingly controls the transfer relay and its N-PE bridge when a mains failure is detected and it switches to inverter operation.
The wiring on the mains input side is clear (changeover switch, RCB, etc.).
Thanks @dennibu, I revisited wiring unlimited and with your text above I realised that the N-E bond moves, therefore the behaviour of the RCD changes depending if on grid or operating in island mode.
So when in grid mode the RCD protects the cable from the RCD to the MP2 and the MP2 themselves. When in island mode the RCD function changes and now protects from RCD to the loads and the loads themselves.
This was the missing part I had, in a normal setup the RCD protection side is a constant as the N-E link is always behind the RCD, this is what was tripping me up!
So based on this, is the best place for the RCD actually at the MP output as this will then protect the 20m underground SWA and the consumer unit from faults if metal etc. In these cases the fault current wouldn’t trip a MCB (so treating the installation as a TT). This is what we would usually do if this was not a remote transfer switch setup and simply an AC out used to supply the house.
Then at the current 4p breaker and RCD point we simply have a MCB to provide over current protection if the SWA get damaged with the RCD at the MP providing fire / cable damage protection to the MPs and associated cables / connections (although this feature will be lost when the N-E link moves to the MP side and the RCD protect is in the opposite direction.
This was the discussion we were having at our end and we got into a bit of a pickle around likely fault cases and best place to have protective devices.
Can I ask why you use an external MEN link as the Victrons have that already integrated inside, you just have to tick the box in VE config…
So, in generator mode, then on the generator you have a fixed hard wired MEN, nothing else…and the RCD will not trip…then…in inverter mode (no grid/no generator) the inverters make the MEN for you and the RCD will not trip.
Ok…another one, no MEN at all, not from the grid/gen nor tick the box…so…no link between earth and neutral in any situation…bad…well…discussion…it works as well but the RCD is very nervous and trips way faster, so, it’s just what you want, remember I work on IMO ships (no earth and steel hull).
So all above is also depending what type of RCD you use.
Personally…In all our installs onshore we never like a MEN-link so much in inverter mode, we like a plain neutral and a plain earth, imagine a lighting bolt hitting close by, it will then go through the MEN into all devices by the neutral and earth together, pffff, in between neutral and phases towards Earth we place surge arresters and so a RCD will work the same, even a bit more nervous which is good…
@Jeroen2 thanks for the reply. The external MEN is used with the external transfer switch configuration, I don’t believe its possible to use the internal MP2 MEN. The MEN is needed for installations otherwise the RCD(s) won’t work and this is not great!
For the 8, 10 and 15k models the external transfer switch is needed when in 3 phase or parallel operation, but also works for a single MP too. This is useful as it saves cables going to both AC-In and AC-Out, means you can use the larger MPs rather than the more expensive Quattro and it reduces cable cost as you don’t need to run to and from the MPs with heavy cables.
I do have a generator input, but it’s a floating earth. I run ESS. I have only tested it because we have so much solar, even when we lose power, and I have a config I can upload to switch from ESS to generator input.
