The complete DC & AC system on a new 40′ boat, in the Victron ecosystem — the AC/DC interface. Shore power & isolation, the MultiPlus-II, PowerControl/PowerAssist, AC & DC distribution (Lynx, SmartShunt, Class-T), MPPT & Orion charging, the Cerbo GX & VRM, and a light NMEA 2000 integration. Built on the required Victron Academy modules and ABYC.
Before you start
Electrical Tech 2 builds the complete DC & AC system on a new 40′ vessel, entirely in the Victron ecosystem, focused on the AC/DC interface: shore power, the MultiPlus, PowerControl/PowerAssist, AC & DC distribution, charge sources, the Cerbo GX brain, and a light NMEA 2000 integration to the chartplotter. It assumes Marine Electrical 1 and the required Victron Online Training modules (free & certificated on Victron Professional). A final exam unlocks your ESI certificate.
Complete the Victron Academy modules; this is the ESI marine layer on top.
The MultiPlus is the heart — shore, transfer, charge, invert, PowerAssist.
Bridge the Victron data onto N2K and the MFD via the Cerbo GX.
Chapter 1
Tech 1 was the fundamentals. Tech 2 is the whole Victron system.
Marine Electrical 1 gave you the fundamentals — volts/amps, wire, fusing, the LiFePO4 bank. Electrical Tech 2 builds the complete DC & AC system on a new 40′ vessel, entirely in the Victron ecosystem, with the focus on the AC/DC interface: shore power, the MultiPlus, charging, distribution, and the GX brain.
ESI is a Victron-standard shop, and you don't learn Victron from us alone — you learn it from Victron. Their Online Training is free, self-paced, and certificated (each module has an exam and a Certificate of Completion) on the Victron Professional portal. Complete the required modules before or alongside this course — this course is the ESI marine wrapper around that training, not a replacement for it.
Victron Online Training is free, self-paced and certificated via the Victron Professional portal; module topics per victronenergy.com/information/training.
Chapter 2
One picture: where AC meets DC.
Before any wire, learn the one-line. Everything hangs off two buses — an AC bus and a DC bus — bridged by the MultiPlus.
| Block | Role |
|---|---|
| Shore / genset (AC in) | The outside AC source — through isolation & protection into the Multi. |
| MultiPlus-II | The inverter/charger — the AC/DC bridge. Charges the bank from AC; inverts DC→AC for loads; built-in transfer switch. |
| AC distribution | AC-out 1 (always, incl. on battery) and AC-out 2 (only with shore/gen) to the AC panel. |
| LiFePO4 bank | The DC store (from Marine Electrical 1) — Epoch, lithium-only. |
| Lynx distributor / busbar | The DC power hub — bank, Multi, chargers and loads all land here, fused. |
| SmartShunt | The battery monitor — true state-of-charge, current, history. |
| MPPT & Orion DC-DC | DC charge sources: solar (MPPT) and engine/start battery (Orion-Tr/XS DC-DC). |
| Cerbo GX + GX Touch / VRM | The brain & display — ties it together, shows it, and reports remotely. |
Chapter 3
Get AC aboard safely before it ever reaches the Multi.
The AC story starts at the dock. Before the MultiPlus ever sees it, shore power passes through protection and isolation.
ABYC E-11-2025 (AC & DC on boats); galvanic isolator / isolation transformer & ELCI marine practice; Victron MultiPlus-II AC-in.
Chapter 4
The single most important box on the boat.
The MultiPlus-II is an inverter + charger + transfer switch in one. It is the AC/DC interface.
Victron MultiPlus-II (two AC outputs, transfer switch, millisecond changeover); VE.Bus to GX.
Chapter 5
The Victron magic that keeps the dock breaker from tripping.
Two features make a Victron system feel effortless on a weak dock.
You set a shore/gen current limit. The Multi will never draw more than that from shore — it throttles its charger so the dock breaker (or a small genset) doesn't trip. On a 15 A pedestal you set 15 A and it lives within it.
When the AC loads briefly exceed the shore limit (kettle + water heater + microwave), PowerAssist tops up the difference from the battery through the inverter, so nothing trips. When the peak passes, the spare shore power goes back to recharging the bank. A 30 A boat runs like it has far more.
Victron MultiPlus-II: PowerControl limits draw from shore/gen; PowerAssist boosts peaks from battery then recharges.
Chapter 6
Critical vs non-critical, and the neutral-ground question.
The Multi's two AC outputs let you decide what runs on battery and what only runs on shore/gen.
When inverting, the Multi bonds neutral to ground internally (a relay) so the ELCI/RCD still works on inverter power; when shore is connected, it releases that bond and uses the shore's. Don't add a second permanent neutral-ground bond — you'll get nuisance trips or defeat protection. AC and DC grounds tie to the boat's common ground per E-11.
Victron MultiPlus-II two-output design & internal ground relay; ABYC E-11-2025 AC grounding.
Chapter 7
The DC bus where everything meets.
On the DC side, the Lynx system is the tidy Victron busbar — bank, Multi, chargers and loads all land on one fused bus.
Victron Lynx Distributor (fused busbar) & SmartShunt; ABYC E-11-2025 + lithium Class-T fusing per ESI Marine Electrical 1.
Chapter 8
The craft that separates a clean install from a fire.
The components are easy; the craft is what fails or lasts. This is how ESI joins, distributes and protects.
A home run is a dedicated conductor from the distribution point (bus/panel) out to one device and back, fused at the source. The alternative — daisy-chaining / tapping several loads off one run — shares faults, stacks voltage drop, and can't be properly fused per device. ESI runs home runs.
Use the correct heavy lug and a full crimp so the connection meets ABYC's tensile / pull-test strength — a proper joint survives years of vibration and a hard pull without the wire backing out. Torque studs to spec. A terminal that passes the pull test is a terminal that won't loosen and heat up.
Form a drip loop at glands, connectors and devices — a low bend so any water runs to the bottom and drips off instead of tracking down the wire into the connector or the back of a unit.
A Class T fuse is slow-blow with very high interrupt capacity: it rides through inverter/motor inrush without nuisance-blowing, yet clears a massive lithium fault. Use it on the lithium main and the inverter feed. Regular (fast) fuses or breakers go on the branch circuits. Match the fuse character to the load — a fast fuse on an inverter feed just nuisance-trips.
US / ABYC boats put the main disconnect on the POSITIVE. Many French / European-built boats (Beneteau, Jeanneau, Lagoon…) switch the NEGATIVE instead. So on a French boat the positive can stay live with the switch “off.” Always verify which pole the disconnect breaks before you assume a circuit is dead.
AC reverses direction 50/60 times a second — that's the “reversing current.” US color code: black = line/hot, white = neutral, green = ground. Because shore wiring can be miswired, the panel carries a reverse-polarity indicator — if line and neutral are swapped, the neutral becomes energized (dangerous) and the indicator warns you. Never ignore it.
Size every conductor for both its current (ABYC ampacity, derated for temperature, bundling and engine-space heat) and its run length (voltage drop — 3% on critical circuits, 10% on non-critical) — then take the larger gauge. Don't eyeball it.
The ESI Wire Calculator (in the hub's Tools section, linked below) does exactly that, straight off the ABYC E-11-2025 tables. You enter: the load in amps, the one-way run length in feet, the system voltage (12/24 V DC or 120/240 V AC), whether the circuit is critical (3% drop) or non-critical (10%), the location (it derates for engine-space heat) and how many conductors are bundled together. It returns the minimum gauge by ampacity (heat) and by voltage drop (length), recommends the larger of the two, and shows the actual voltage-drop % at that size — so the gauge you cut has the numbers behind it. If it pushes past 4/0, it tells you to split the circuit or go to 24 V.
ABYC E-11-2025 (ampacity, voltage drop 3%/10%, terminal pull-test, positive-terminal protection); Wirefy 3:1 heat-shrink connectors; WAGO 221 dry-location rating; BEP/Egis bus bars; US positive vs EU negative battery disconnect convention.
Chapter 9
Filling the bank from sun and engine, the Victron way.
Besides the Multi charging from AC, the DC bank fills from solar and the engine.
A Victron MPPT (SmartSolar / BlueSolar) tracks the panel's maximum-power point and charges the bank with a lithium charge profile. Size it to the array; it reports over VE.Direct to the GX.
To charge the lithium bank from the engine you either fit an externally-regulated alternator (see the ESI Alternator Charging course — WS500/MC-618) or, for a modest top-up off the start side, a Victron Orion-Tr / Orion XS DC-DC charger: it takes the start-battery/alternator feed and delivers a clean, current-limited lithium charge without overloading a stock alternator.
Victron SmartSolar MPPT & Orion-Tr/XS DC-DC; cross-ref ESI Alternator Charging (external regulation).
Chapter 10
Tie it together, see it, and watch it from anywhere.
The Cerbo GX (or Ekrano GX) is the system's controller and gateway.
Victron Cerbo GX / Ekrano GX, GX Touch, VRM (remote monitoring, alarms, firmware).
Chapter 11
Put the Victron data on the chartplotter.
A light touch — enough to get the Victron system onto the boat's NMEA 2000 network and the chartplotter. (Full N2K is its own subject.)
Victron VE.Can → NMEA 2000 integration (GX NMEA 2000-out bridges Victron data to the MFD); NMEA 2000 backbone/drop/terminator/power basics (Actisense, Maretron).
Chapter 12
Configure it, prove it, hand it over.
The system isn't done until it's configured for lithium and every mode is proven.
VictronConnect / VE.Configure (charge profiles, PowerControl/PowerAssist, Assistants); Epoch LiFePO4 charge spec; ESI commissioning standard.
Field reference
Field-tested: the symptom, the usual cause, and the fix. Always diagnose before you replace parts.
| Symptom | Likely cause | Fix |
|---|---|---|
| No shore charging | Tripped ELCI/breaker, reverse polarity, or an open galvanic isolator | Check the breaker & polarity light, test the isolator, confirm the shore feed |
| MultiPlus won’t pass shore power | Input current limit too low, “ignore AC” on, or overload | Set the input limit, enable AC-in, check PowerAssist and the loads |
| Inverter drops out under load | Low SOC, BMS disconnect, undersized DC cable, or a blown fuse | Check SOC & BMS, verify the Class-T fuse, upsize the cable to the wire calc |
| MPPT not charging | PV below battery voltage, reversed or shaded array, or a blown PV fuse | Verify Voc > battery, correct polarity, clear shading, check the fuse |
| Cerbo GX shows no device data | VE.Direct/CAN cable, missing terminators, or no power | Reseat the cabling, fit both CAN terminators, confirm device power |
| Dim lights / voltage drop | Undersized wire, a bad crimp, or a corroded lug | Re-size per the ABYC wire calc, redo the crimp with adhesive heat-shrink, clean the lug |
| Class-T or a fuse blows | A short or a sustained overload | Find and clear the fault first — never up-size a fuse to stop nuisance blows |
| Lithium won’t accept charge | BMS low-temperature cutoff or fault | Warm the bank above the BMS limit / enable the heater, read the BMS status |
Final certification
A short check ran at the end of each chapter. Pass this final at 80% to unlock your certificate.