The premise
Three Multiplus 5 kVA inverters are heavy. Together they handle three phases worth of current. Whatever wall they hang on has to take the weight, and whatever wiring layout sits behind them has to keep cables short, organised, and accessible. This video is the preparation step: mounting board, wiring trunking, the first Multiplus on the wall, and the cable trough between the meter box and the storage room.
Most of the build only works if this step is done carefully. Robbert spends the time on layout before drilling anything.
Laying out the wall
A heavy plywood board goes against the wall with hefty bolts. The Multiplus units screw straight through the board and into the wall behind it, not into the wood alone. The board is the structure for the wiring; the wall carries the weight.
Before mounting the board, Robbert measures everything and draws the layout on the plywood itself. Where the Multiplus units go, where the busbars go, where the Cerbo goes, where the screen mount could go later. The reason is dull and important. Shorter cables mean lower losses. Lower losses mean a more efficient system. Sketching the layout in advance is the cheap way to spot wasted distance before it becomes permanent.
Why wiring trunking and not just cable channel
Robbert uses 40x60 mm wiring trunking with side slots, not closed cable channel. Two reasons.
First, the slots let him route a cable out of the side wherever he needs to, without drilling new holes. He can tap off a feed at any point along the run.
Second, the trunking lets him mount sections at 90 degrees to each other. The fingers between slots can be snapped off where a cable needs to turn a corner, so wires don't have to bend at sharp angles or run outside the trunking.
The trunking is heavy enough to carry 70 mm² battery cables between the Multiplus and the busbars, and easy enough to route from the trunking into the battery cabinet itself.
The battery cabinet feed-through
A hole gets drilled in the top of the steel battery cabinet so cables can enter from the trunking. After the cables go in, the hole is sealed as well as possible. The reason is fire safety. Robbert wants nothing metallic to fall into the cabinet from above, and wants no debris reaching the cells.
Mounting the first Multiplus
There are two ways to mount a Multiplus. The supplied bracket screws to the wall and the unit hangs on it. Or the unit screws directly through its four rear holes into the wall behind. Robbert chooses the second method. It is a permanent installation, the unit is heavy, and bolting through gives a stronger anchor.
He admits on camera that the units are awkwardly heavy and credits a helper for the lift.
For viewers new to a Victron setup, Robbert gives the short version of what a Multiplus actually does. It is a battery charger and an inverter in one box. It can move energy from grid to battery, or from battery back to 230 V. The transitions happen fast. The Cerbo is the brain that tells each Multiplus when to charge and when to discharge based on what the rest of the system is doing.
Cerbo and the cable bedroom
The Cerbo mounts in the bottom right of the board. The position leaves room on the left for the main busbar, which sits where the battery cabinet cables emerge. From the busbar, current can flow up to the Multiplus units, or back down for discharge.
Robbert wants the readout screen in the living room, not next to the inverters. A cable will run from the Cerbo to a small display indoors. The advantage of the wiring trunking shows up here: he can route the Cerbo's data cable along the trunking, drop it out wherever he wants, and have a clean finish without drilling new exit holes.
The cable run to the storage area
The original cable trough between the meter box and the storage area was sized for a single light and a couple of outlets in the shed. It needs replacing.
Robbert rips out the existing trough and installs a closed cable trunking large enough for two 5-conductor 6 mm² power cables. One cable feeds power from the meter box main switch out to the Multiplus units. The other cable returns the inverter output to the meter box, where it feeds the original group circuits.
The meter box already has three extra group breakers Robbert added earlier for solar strings, each on a separate phase. Two of them are in use. The third is reserved for the next string when it goes in.
The trunking is mounted along the ceiling. End caps are 3D-printed. Robbert plans to share the print files.
Takeaways
- A plywood mounting board lets you screw trunking and Multiplus brackets wherever needed, without hunting for studs each time. Bolt the board to the wall first.
- Wiring trunking with side slots beats closed cable channel for inverter installs. The slots let cables exit at any point.
- The Multiplus is heavy enough that the supplied wall bracket is the second-best option. Bolting through the back is more secure.
- Plan layouts on the board before drilling. Marker on plywood is cheaper than rework.
- Replace undersized cable trough between the meter box and the storage area before pulling any 6 mm² cable through. The space matters.
