MPII and House DB Board

Hi Guys,

Long story short, I am swopping out all my equipment to Victron and now in the same breath trying to re-wire my db and I need guidance what the sparky must so its proper and taking into account Coct requirements.

Current DB is 1973 samite buzzing board, everything is being taken out and a new DIN rail board is going into its place.

My solar install is back to back, my kitchen has the main db and other side is the garage, the main db is not split currently, I want to split it this time work with the Multiplus and to handle the heavy loads better

As it stands, Cables runs like follows,
Grid—>63Amp Mainswitch / Earth Leakage
—> Coct Prepaid Meter
—>60Amp Breaker
—>through wall to sub db garage side
—>60Amp Breaker that feeds a 40amp breaker (inverter AC IN). as well as input 1 on rotary changeover switch.

Inverter AC out
—> input 2 to changeover switch

Changeover output
—> back through wall to main db
—> 40amp breaker
----> feed entire db

What I want to have in the new db, essential (AC OUT1) and non essential (AC OUT2) loads
Will retain the current changeover and wire MP AC OUT1 to it
Get another changeover and wire grid and AC OUT2 to its inputs, will need another set of cables for the output going back to feed non essential part of db.

The changeovers are for in case of maintenance, being able to fully return to eskom.

If you look at all the current setup and what I want to do, how would you implement the wiring and use which breakers where, ie. db design, breaker sizes etc etc

Please ask if unclear, it probably is a bit :smiley:

Thanks !!

I guess , some else will also weigh in here but I think you are a bit optimistic in thinking a whole DB design will be done here. May I suggest you start by drawing up a basic diagram of how you like it to look.
Firtz Box might help. Be mind full of the amount of CB you can take in a row and how many rows you have as this will determine your design.
It might also be well worth it to get an Electrician (don’ use a sparky) to have a look at your setup as they have a very good idea as to what works and what doesn’t.
Any way , enjoy your Victron!

The electrician should decide with the breaker sizes. The breakers depend on the wires used. Get someone that understands a Victron install.

With a Victron install, depending on your individual circumstances, if you redo the whole thing, you only actually need one AC DB (as per my understanding), switch you can split into essential and non-essential circuits.

To comply with CoCT, you need to first submit your proposed system to them, indicating what you want to apply for. That should include a single line diagram with all the parts used on it.

Regarding the line drawing, CoCT are big on the change over switch, clearly show that grid and the inverter supply are separate.

1 Like

Me, I would install a Carlo Gavazzi just after the main breaker in the main DB.
And not use the AC_Out2 at all. It just complicates matters unnecessarily.

Why does it complicate it? I assumed that it is less complicated that way?

If you connect the entire house i.e. both Main DB and Always on DB onto the same inverter via AC_Out2 and AC-Out1, then both DB’s draw is limited to the max of the inverter.

If you don’t use AC_Out2, and install a Carlo Gavazzi just after the main street breaker on the main DB, then only the Critical Loads/Always ON DB is limitted to the max of the inverter.

AC_IN1, which connects the inverter to the main DB, will feed the main DB up to the point of the Carlo, tryng to limit the entire house Eskom draw, saving you the most with ESS.

Simpler, easier and less DB work and the inverter feeds both DB’s.
You only worry about the 2nd Always On/Critical loads DB, leave the main DB as is.

Well, 50A (70A if you have PV/batteries available) should be ample for most houses?

i have 3 phase supply but each phase is limited by a 35 amp three phase combined breaker, so i made one phase the inverter circuit and the 32 amp capacity of the MP II worked out just fine.

Those amps are DC amps of the inverter.

So if you have the kettle on, 2kw, microwave, 2kw and the wife switch on the induction plate, you exceed a 5kva’s ability, inverter switches off.

Or the geyser is on, if 4kw, than the 5kva is maxed.
If 2kw element you can boil the kettle if it draws 2kw.
Anything else comes on, the inverter switches off.

A house can use 63a at 230v AC = ±14kw in total.

Don’t use AC_Out2 is my suggestion.
Get a Carlo Gavazzi which also gives you very detail Eskom usage data.

Nope, 50A is the transfer capacity on the AC side. The additional 20 Amps is inverting capacity from the DC side.

So the MPII 5kVA can handle at a minimum 11.5kW as long as Eskom is up.

Hi @TheTerribleTriplet, now I am confused, i have seen over 6000 watts on the VRM, and I have a 3 kVa Easysolar II, granted the inverter only supplies 2400 watts and the rest comes from the grid. Am i missing something.
I use AC-OUT-2

If the 3kVA Easolar II has the inverter of the MPII 3kVA in, I believe it has a transfer rating of 32A with another 12/13A from the DC side, so the inverter should be able to handle about at least 7.5kW when Eskom is available plus an additional 3kW when PV/Battery is also available.

yes, it is a MP II with a GX card and 250/70 mppt

The point I’m trying to convey, to simplify a install, is that if you don’t use AC_Out2, but a Carlo Gavazzi instead, it may be simpler and easier.

Then you don’t have to worry about the max the inverter can do, only worry about the max draw of loads when Eskom is off on AC_Out1, as the inverter, via AC_In1, will feed power to all the loads in the house, so no matter that a geyser (2) + kettle (2) + MV (2) + stove (4) + hairdryer (2) (= 12kw) are all on, inverter will feed all it can to off-set that draw from Eskom i.e. 12kw - 4kw (5kva) from primarily the panels and some batts based on SOC.

It is not the ONLY way, but the most simplest way, if one grid ties

A Carlo is wot ±R1100 and you get detailed data from it too.
Main DB just needs the Carlo installed, and a double pole breaker to the inverter - Main DB is then sorted.
Then you take all the circuits you want to power off batts, out of the main DB and put them into the 2nd Always On/Critical loads DB, connected to AC_Out1, with the main focus being that these loads are battery dependent if Eskom is off and there is no solar.

If Eskom is on, 2nd DB AND the main DB will be fed all that the inverter can feed based on panel production and batteries, to the SOC selected.

But if anyone wants to use AC_Out2, by all means!

But you will get that same data if all the power runs through the inverter?

I’m not an installer, but I am sure I remember @JacoDeJongh saying once that it is nicer to run the whole house through the inverter. Definitely the two guys installing my system said they normally do that, but it was too difficult at my house (inverter is not on the same floor as main DB).

In a lot of cases it is better, in some cases its not possible and in most its less work.

The result of connecting a Carlo or Using AC-Out2 is the same at the end.


@plonkster Is the control loop quicker when not including the Carlo? Basically, will it be quicker to pick up changes in large loads an manage how much it is pushing “back” into the grid?

Yes. It is faster without the external meter. But if you’re worried about a tripping prepaid meter, don’t bet on this to fix it.

1 Like

Nah, we were mainly discussing the benefits of running the whole house through the MPII or not.

So in general, it sounds like it is preferable to run the non-essentials through the AC-Out 2, as it is cheaper and easier and the control loop is faster (not that we need to care too much about it).

This is if you think a minimum restriction of 50A is okay for you (ignoring the potential PV/battery uplift), which it should be on most houses with 63A main breakers.