Three-phase backup power with just one 5×16 mm² cable and an external transfer switch

DIY
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1

Hello everyone,

I am planning a three-phase Victron ESS and would like to clarify whether it can be implemented with only one AC cable each to the MultiPluses.

Components:
3× MultiPlus-II 48/6k5
NKON ESS Pro 32.15 kWh
SMA Sunny Tripower X 20, 24.94 kWp PV
Sunny Home Manager 2.0
Cerbo GX
TN-C-S system; PEN split into PE and N in the main low-voltage switchboard (NSHV)

The MultiPluses and the battery are to be installed in the garage. The Sunny Tripower is located in the house, in the attic.

Unfortunately, there is currently only one cable between the main low-voltage switchboard and the garage:
NSHV → boiler room → garage: 5×16 mm² Total length approx. 45 m
plus 4× Cat 7 and 2× J-Y(St)Y 4×2×0.8
OS2 single-mode fibre-optic cable in future
The garden has only just been reinstated, and of course the conduits were chosen too small—don’t ask…

Main question

Can the existing 5×16 mm² cable be used in grid-connected operation as the connection to the garage and, after suitable all-pole grid isolation, as an AC-out connection back to the NSHV or the entire house network?

I am thinking of an “External Transfer Switch Application” with the grid disconnected in the NSHV.

This raises the following questions:

Is there another Victron-supported topology in which the 5×16 mm² cable can be used in both grid-connected and backup-power operation?

In the “External Transfer Switch Application”, can an EM540 replace the voltage path directly connected to the MultiPlus (AC IN) and the connected current transformers, or is it suitable exclusively as a grid meter for normal ESS control? Can its voltage measurements also be used, or are the separate AC-IN voltage-sensing cables to the MultiPluses still essential?

Ziehl UFR1001E and Sunny Tripower

The Victron Anti-Islanding Box with the Ziehl UFR1001E caught my eye. As I understand it, the Ziehl takes care of external grid and system protection and controls or monitors the grid-isolation contactors.

The Sunny Tripower X also has:
DI6 for external grid and system protection or rapid shutdown
DI1–DI4 for external active-power setpoints

Would the following sequence be technically possible and, if applicable, even approved by Victron and SMA?

The Ziehl detects the failure of the public grid.
The grid-isolation contactors open all poles.
At the same time, the Sunny is initially stopped via DI6.
The MultiPluses establish the three-phase island grid.
The Sunny is enabled again.
In island operation, a maximum active power of approximately 10 kW is continuously specified via DI1–DI4.
The P(f) control then takes over ongoing power adjustment.

Would this work, or am I missing something?

For now, I am looking for a fundamentally functional and officially supported topology that does not require installing a second power or voltage-sensing cable between the house and the garage. This concept will then be discussed with the electrician working on the house and property.

Thank you very much for your help.
Best regards

4

There isn’t one.
I’m sure it would be possible to find a solution that works, but it probably wouldn’t be officially supported.

In theory, it should work, but not without the appropriate sensor/control cables between the house and the garage.
Everything within the red area can go in the garage; everything else has to be in the house.

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In other words, you need L1, L2, L3 and N from the house to the garage for synchronisation with the grid; a 5x1.5 cable would be sufficient for that.
You also need 2 cores to control contactor C. Since these carry 230 V, this would also have to be a 3-core cable, although 3x1.5 would be sufficient.
However, you don’t have suitable cables installed for either of these.

The biggest problem, however, will be the three CTs. As far as I know, they are always required, even if you also have, for example, an EM540 as a grid sensor.
The CTs replace the internal sensors of the MultiPlus, which are no longer used due to the S99 FW because the AC IN relays are always open.
You could get the signals to the garage via the existing cables, but the measurement would probably be distorted due to the length.

Are the Cat and Jysty cables in the same conduit, or are they all separate?

Why can’t the Victron system be installed in the house?

5

Thank you very much for your detailed reply! I had already feared as much.
What kind of potential solution not approved by Victron do you have in mind?

There are two conduits to the garage:
1x conduit → NYY-J 5x16mm²
1x conduit → 2x duplex Cat7, 2x YSTY and soon another 12 single-mode OS2 fibre-optic cables

Why can’t the Victron system be installed in the house?

The usual problem: there’s no room.
The house has no basement, and the boiler room is full thanks to the heat pump and 2x 800-litre buffer tanks.
There would still be room in the uninsulated loft, but temperatures there are hot in summer and cold in winter. The 240 kg storage unit would also have to be moved into the loft. :smiling_face_with_tear:

6

How big is the conduit?, is it not an option to pull out all cables and start over again?.. this time with only 5x10 mm double AC powercables, 5x16 is overkill, yes two 5x10 mm cables plus all others cables, with water based 3M lube and no twist in the cables before pulling it might be possible, (2 man’s job, one pulling other pushing)

7

Alternatively, pull out the copper from the second conduit and put in a 5x16 + the optical cable, that should be legal.

8

The one I described above.

Another, but unsafe, option would be to switch AC IN and AC OUT using switches.
That would mean there was no automatic changeover, and you would always have to operate the switches in the correct order; otherwise you could end up connecting the mains to AC OUT and there would be a bang.
This is absolutely not recommended.

Another idea would be to use the “data conduit” for an additional AC cable.
Depending on how large the conduit is, you might still be able to pull one or two additional data cables through it, even though you normally shouldn’t do that.
You basically don’t need more than one network connection there anyway, if you use a network sensor that communicates via LAN, or perhaps a YStY cable for the EM540’s RS485.
That shouldn’t matter to a fibre-optic cable either.

Or, alternatively, dig after all and install another cable.