MultiPlus-II 12V/24V/48V 3kVA 120V

4. Installation

In this section:


This product may only be installed by a qualified electrical engineer.

4.1. Location

The product must be installed in a dry and well-ventilated area, as close as possible to the batteries. There should be a clear space of at least 10 cm around the appliance for cooling.


Excessively high ambient temperature will result in the following:

  • Reduced service life.

  • Reduced charging current.

  • Reduced peak capacity, or shutdown of the inverter.

Never position the appliance directly above the batteries.

The MultiPlus-II is suitable for wall mounting. A solid surface, suitable for the weight and dimensions of the product must be available (e.g., concrete, or masonry). For mounting purposes, a hook and two holes are provided at the back of the casing (see appendix G).


The interior of the product must remain accessible after installation.

Try and keep the distance between the product and the battery to a minimum in order to minimize cable voltage losses.


For safety purposes, this product should be installed in a heat-resistant environment. You should prevent the presence of e.g. chemicals, synthetic components, curtains or other textiles, etc., in the immediate vicinity.


Each system requires a method of disconnecting the AC and DC circuits. If the overcurrent protection device is a circuit breaker, it will also serve as the disconnect. If fuses are used, separate disconnect switches will be needed between the source and the fuses.


To reduce the risk of fire, do not connect to an ac load center (circuit breaker panel) having multiwire branch circuits connected.


CAUTION – To reduce risk of injury, charge only Lead Acid or LIFEPO4 type rechargeable batteries. Other types of batteries may burst causing personal injury and damage


Use of an attachment not recommended or sold by the marine unit manufacturer may result in a risk of fire, electric shock, or injury to persons




  • Someone should be within range of your voice or close enough to come to your aid when you work near a lead-acid battery

  • Have plenty of fresh water and soap nearby in case battery acid contacts skin, clothing, or eyes.

  • Wear complete eye protection and clothing protection. Avoid touching eyes while working near battery.

  • If battery acid contacts skin or clothing, wash immediately with soap and water. If acid enters eye, immediately flood eye with running cold water for at least 10 min and get medical attention immediately.

  • NEVER smoke or allow a spark or flame in vicinity of battery or engine.

  • Be extra cautious to reduce risk of dropping a metal tool onto battery. It might spark or short-circuit battery or other electrical part that may cause explosion.

  • Remove personal metal items such as rings, bracelets, necklaces, and watches when working with a lead-acid battery. A lead-acid battery can produce a short-circuit current high enough to weld a ring or the like to metal, causing a severe burn.

  • NEVER charge a frozen battery.

  • If necessary to remove battery from vessel, always remove grounded terminal from battery first. Make sure all accessories in the vessels are off, so as not to cause an arc.

  • Be sure area around battery is well ventilated. Clean battery terminals. Be careful to keep corrosion from coming in contact with eyes. Study all battery manufacturer’s specific precautions such as removing or not removing cell caps while charging and recommended rates of charge.

  • Clean battery terminals. Be careful to keep corrosion from coming in contact with eyes.

  • Study all battery manufacturer’s specific precautions such as removing or not removing cell caps while charging and recommended rates of charge.



  • Locate marine unit away from battery in a separate, well ventilated compartment

  • Never place marine unit directly above battery; gases from battery will corrode and damage marine unit.

  • Never allow battery acid to drip on marine unit when reading gravity or filling battery.

  • Do not operate marine unit in a closed-in area or restrict ventilation in any way.



Connect and disconnect DC output connections only after setting any marine unit switches to off position and removing AC cord from electric outlet or opening AC disconnect.




GROUNDING INSTRUCTIONS – This marine unit should be connected to a grounded, metal, permanent wiring system; or an equipment-grounding conductor should be run with circuit conductors and connected to equipment-grounding terminal or lead on unit. Connections to unit should comply with all local codes and ordinances

4.2. Connection of battery cables

In order to utilize the full capacity of the product, batteries with sufficient capacity and battery cables with sufficient cross-section should be used. The DC cables must be copper and rated 90ºC (194ºF). See table.




Recommended battery capacity (Ah)




Recommended DC fuse

400 A

300 A

125 A

Recommended cross section (mm2 ) per + and - connection terminal *, **

0 – 5 m***

2x AWG 1/0

AWG 1/0


5 – 10 m***

2x AWG 2/0

2x AWG 1/0

AWG 2/0

* Follow local installation rules.

** Do not locate battery cables in a closed conduit

*** “2x” means two positive and two negative cables.

Remark: Internal resistance is the important factor when working with low capacity batteries. Please consult your supplier or the relevant sections of our book ‘Energy Unlimited’, downloadable from our website.


Proceed as follows to connect the battery cables:


Use a torque wrench with an insulated box spanner in order to avoid shorting the battery.

Recommended torque: 12 Nm (M8 nut)

Avoid shorting the battery cables.

  • Undo the two screws at the bottom of the enclosure and remove the service panel

  • Connect the battery cables: see Appendix A

  • Tighten the nuts well for minimal contact resistance.

  • The connector goes on first, then the flat washer, lock washer and  nut. Tighten the nuts well for minimal contact resistance.


4.3. Connection of the AC cabling


The MultiPlus-II is a safety class I product (supplied with a ground terminal for safety purposes). Its AC input and/or output terminals and/or grounding point on the outside of the product must be provided with an uninterruptible grounding point for safety purposes.

The MultiPlus-II is provided with a ground relay (relay H, see appendix B) that automatically connects the Neutral output to the chassis if no external AC supply is available. If an external AC supply is provided, the ground relay H will open before the input safety relay closes. This ensures the correct operation of an earth leakage circuit breaker that is connected to the output.

  • In a fixed installation, an uninterruptable grounding can be secured by means of the grounding wire of the AC input. Otherwise the casing must be grounded.

  • In a mobile installation (for example, with a shore current plug), interrupting the shore connection will simultaneously disconnect the grounding connection. In that case, the casing must be connected to the chassis (of the vehicle) or to the hull or grounding plate (of the boat).

In case of a boat, direct connection to the shore ground is not recommended because of potential galvanic corrosion. The solution to this is using an isolation transformer.


This unit or system is provided with fixed trip limits and shall not be aggregated above 30 kw on a single point of common connection.

A blade tool of 2.5mm (e.g. a screwdriver) is required to operate the spring loaded AC terminal blocks.

The terminal blocks can be found on the printed circuit board, see Appendix A.

Do not invert neutral and phase when connecting the AC.

The shore or mains cable must be connected to the Multi with the aid of a three-wire 90ºC (194ºF) copper cable.




Rated current

50 A

75 A

32 A

Recommend fuse or circuit breaker

50 A

75 A

32 A

Minimum wire gauge



AWG 10

Ferrule pin length / stripping length

0.7 inch (18 mm)

0.7 inch (18 mm)

0.7 inch (18 mm)

The inverter does incorporate a mains frequency isolating transformer. This precludes the possibility of DC current at any AC port.

Therefore type A RCD’s can be used.

  • AC-in

    The AC input cable can be connected to the terminal block ‘AC–in’.

    From left to right: “N” (neutral), “L2” (phase 2), “PE” (earth) and “L1” (phase 1)

    The AC input must be protected by a fuse or magnetic circuit breaker rated at 50A or less, and cable cross-section must be sized accordingly. If the input AC supply is rated at a lower value, the fuse or magnetic circuit breaker should be down sized accordingly.

  • AC-out-1

    The AC output cable can be connected directly to the terminal block ‘AC-out’.

    From left to right: “N” (neutral), “PE” (earth)  and “L” (phase)

    With its PowerAssist feature the Multi can add up to 3kVA (that is 3000 / 120 = 25A) to the output L1 during periods of peak power requirement. Together with a maximum input current of 50A this means that the output can supply up to 50 + 25 = 75 A. An earth leakage circuit breaker and a fuse or circuit breaker rated to support the expected load must be included in series with the output, and cable cross-section must be sized accordingly. Victron Energy recommends to use the Blue Sea systems GFCI circuit breakersPN. 309X or 310X. The maximum rating of the fuse or circuit breaker is 75A.

  • AC-out-2

    A second output is available that disconnects its load in the event of battery operation. On these terminals, equipment is connected that may only operate if AC voltage is available on AC-in-1, e.g. an electric boiler or an air conditioner. The load on AC-out-2 is disconnected immediately when the MultiPlus-II switches to battery operation. After AC power becomes available on AC-in-1, the load on AC-out-2 will be reconnected with a delay of approximately 2 minutes. This to allow a genset to stabilise.

4.4. Optional Connections

A number of optional connections are possible:

4.4.1. Remote Control

The product can be remotely controlled in two ways.

  • With an external switch (connection terminal M, see appendix A). Operates only if the switch on the MultiPlus-II is set to “on”.

  • With a Multi Control panel (connected to one of the two RJ45 sockets L, see appendix A). Operates only if the switch on the MultiPlus-II is set to “on”.

4.4.2. Programmable relay

The product is equipped with a programmable relay.

The relay can be programmed for all kinds of other applications however, for example as a starter relay for a generator.

4.4.3. Programmable analog/digital input/output ports

The product is equipped with 2 analog/digital input/output ports.

These ports can be used for several purposes. One application is communication with the BMS of a lithium-ion battery.

4.4.4. Voltage sense (connection terminal J, see appendix A)

For compensating possible cable losses during charging, two sense wires can be connected with which the voltage directly on the battery or on the positive and negative distribution points can be measured. Use wire with a cross-section of 0,75mm².

During battery charging, the MultiPlus-II will compensate the voltage drop over the DC cables up to a maximum of 1 Volt (i.e. 1V over the positive connection and 1V over the negative connection). If the voltage drop threatens to become larger than 1V, the charging current is limited in such a way that the voltage drop remains limited to 1V.

4.4.5. Temperature sensor (connection terminal J, see appendix A)

For temperature-compensated charging, the temperature sensor (supplied with the MultiPlus-II) can be connected. The sensor is isolated and must be fitted to the negative terminal of the battery.

4.4.6. Parallel Connection

Up to six identical units can be connected in parallel. When connecting MultiPlus-II units in parallel, the following requirements must be met:

  • All units must be connected to the same battery.

  • A maximum of six units can be connected in parallel.

  • Only identical devices may be connected in parallel.

  • The DC connection cables to the devices must be of equal length and cross-section.

  • If a positive and a negative DC distribution point is used, the cross-section of the connection between the batteries and the DC distribution point must at least equal the sum of the required cross-sections of the connections between the distribution point and the MultiPlus-II units.

  • Place the MultiPlus-II units close to each other, but allow at least 10cm for ventilation purposes under, above and beside the units.

  • It is essential the negative battery terminal between the units is always connected. A fuse or circuit breaker is not allowed.

  • UTP cables must be connected directly from one unit to the other (and to the remote panel). Connection or splitter boxes are not permitted.

  • Always interconnect the negative battery cables before placing the UTP cables.

  • Only one remote control means (panel or switch) can be connected to the system.

4.4.7. Split-phase and three-phase operation

The MultiPlus-II can also be used in split-phase and in 3-phase wye (Y) configuration. To this end, a connection between the devices is made by means of standard RJ45 UTP cables (the same as for parallel operation). The system (MultiPlus-II plus an optional control panel) will require subsequently configuration (see Section 5).

Note: the MultiPlus-II is not suitable for 3-phase delta (Δ) configuration