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MultiPlus-II External Transfer Switch application

3. Installation

In this section:
MultiPlus-II_external_transfer_switch_-_wiring_diagram.png

A

AC voltage measurement wires, connected to the MultiPlus-II AC-IN terminals.

B

Current transformers for MultiPlus-II, connected to the MultiPlus-II current transformer terminals.

C

External transfer switch, driven by the MultiPlus-II programmable relay (AUX relay) terminals.

D

Ground help relay, driven by the MultiPlus-II external ground relay terminals.

E

Ground relay, driven by the ground help relay.

F

Additional MultiPlus-II units can be paralleled in each phase with only their AC-OUT and VE.Bus terminals connected.

For the full-size diagram, see the Wiring diagram section.

Warning

Parallel and multiphase systems are complex. We do not support or recommend untrained or inexperienced installers working on these systems.

Before the system's initial power-up, double-check all wiring. Wiring mistakes can damage the MultiPlus-II units.

3.1. AC voltage measurement

The MultiPlus-II's AC input functions as a measuring input. Since the internal back-feed relay is not used, the wires can be relatively thin, 1.5mm² wires are sufficient.

Connection procedure:

  1. Connect the AC-IN terminals of MultiPlus-II to the generator AC supply.

  2. For paralleled units, connect only the master unit (of each phase) to the AC-IN terminal and leave the slave units' AC-IN terminals unconnected.

  3. Use a 6A four-pole circuit breaker to fuse the line and neutral wires.

3.2. Current transformer

The current transformers for each phase (L1, L2, and L3) are connected to the “Current Sense” inputs on the respective phase master MultiPlus-II units:

Connection procedure:

  1. Remove the wire bridge between the INT and COM terminals.

  2. Connect the red sensor wire to the EXT terminal and the white sensor wire to the COM terminal.

  3. Ensure the wire direction through the current sensor follows the arrow pointing from the generator to the MultiPlus-II.

MultiPlus-II_external_transfer_switch_-_connection_CT_1.png
MultiPlus-II_external_transfer_switch_-_connection_CT_2.png

Important notes:

  • Avoid routing current sensor wiring parallel and close to AC power wiring, signal wiring or VE.Bus wiring to prevent signal interference.

  • The 400A current transformer has a reduced current sensing resolution, especially at low currents.

Compatible current transformers:

  • CRT12XXXXXX: Current Transformer 100A:50mA for MultiPlus-II Wire-end (available in 1.5 and 20m cable length).

  • CTR140050100: Current Transformer 400A:50mA for MultiPlus-II (10m) Wire-end (the current sensor wiring can be extended up to 20m using 0.75mm² wire).

  • CRT11XXXXXXX: Current Transformer 100A:50mA for MultiPlus-II Jack connector (for older MultiPlus-II units, available in 1.5 or 20m length).

For more information, see: https://www.victronenergy.com/meters-and-sensors/current-transformer-for-multiplus-ii.

3.3. Ground relay

The ground relay drive signal is supplied by the MultiPlus-II “Ext GND Relay” terminals of the L1 phase master unit via a help relay.

Since the “Ext GND Relay” output signal is limited to 24V / 200mA, a help relay with a 24V coil must be used to switch the actual ground relay.

The ground relay rating must match the total inverter power of the system.

Connection procedure:

  1. Connect the help relay coil terminals to the MultiPlus-II "Ext. GND Relay" terminals.

  2. Connect the help relay power terminals to L1 MultiPlus AC-OUT L terminal and one of the Ground relay coil terminals. Fuse this wire with a 2A fuse.

  3. Connect the remaining ground relay coil terminal to the L1 MultiPlus-II AC-OUT N terminal.

  4. Connect the ground relay power terminals between The MultiPlus-II GND and AC-OUT N terminals.

MultiPlus-II_external_transfer_switch_-_connection_GND_relay.png

3.4. External transfer switch

Any standard contactor can be used.

Since inverter current flows through the AC outputs of the MultiPlus-II units, ensure the external transfer contactor wiring is appropriately sized and symmetrical.

Connection procedure:

  1. Connect the contactor coil directly to the NO and COM terminals of the MultiPlus-II "AUX RELAY" terminals of the L1 phase master unit. Fuse this wire with a 2A fuse.

  2. Connect one side of the contactor power terminals to the generator.

  3. Connect the other side of the contactor power terminals to the AC-OUT terminals or the MultiPlus-II units and the AC loads.

  4. Protect the AC output wiring with a circuit breaker suitable for the expected load and wire gauge. Fuse both line and neutral wiring.

MultiPlus-II_external_transfer_switch_-_connection_AUX_relay.png