Sizing DC cables Between Multiplus 12/1200/50 230V and Lynx M10

Been through this exact headache on my boat last summer. Victron's own docs point you toward 35mm² for the 12/1200/50 and honestly I'd not stray too far from that, especially on a 12v system where the currents are brutally high compared to 24v.

The thing people underestimate is voltage drop on short, fat cables at 12v matters way more than it does on a 48v system. Even a fraction of a volt lost in the cable under load can cause the Multiplus to behave oddly — seen it trip on low voltage warnings when the battery was genuinely fine.

That said, cable run length is everything here. If you're talking under half a metre each side to the Lynx, some folks get away with good quality 25mm² tinned marine cable with solid lugs and clean connections. Fogstar and others sell decent pre-made options. But I'd still say 35mm² is the right call if you're doing it properly.

Worth checking:

• Are your lugs actually rated and crimped properly? A dodgy crimp on undersized cable is a fire risk
• Fuse sizing at the battery end — Victron recommend 125A for that unit
• Keep runs as short and symmetrical as possible to the Lynx busbars

Anyone else running 25mm² on a 12/1200 without issues? Curious what the real-world experience is — particularly on boats where short runs are the norm anyway. Feels like there's a gap between what Victron spec and what people actually use without problems.

@BazBurns yes, the 35mm² recommendation exists for a reason on 12v — the current draw is brutal compared to 24v or 48v equivalents.

When I wired my motorhome build last year I went 50mm² between my Multiplus and the Lynx just to keep voltage drop negligible over the run length (mine was pushing 900mm each way). Overkill some might say, but on a 12v system every millivolt counts under full load.

One thing that catches people out — keep those runs as short as physically possible. I've seen lovely installs ruined by someone routing cables around the entire hab section to keep things "tidy." The Lynx M10 positioning matters more than people realise.

Also torque your M10 connections properly. Victron specifies it and loose connections on high-current DC are genuinely dangerous rather than just inefficient.

@Nessa68 is right, and here's the thing people forget — it's not just the steady-state draw you're sizing for. That MultiPlus will cheerfully gulp around 230A at peak on 12V, and that's before it's had its morning coffee. I learned this the hard way in my shepherd's hut build when I ran a slightly undersized run "just temporarily" between my Fogstar battery and the Lynx distributor. Three months later, "temporarily" had become a warm cable and a mild sense of dread every time the kettle clicked on.

Worth noting: cable length matters enormously on 12V. Even a short run with marginal cross-section will cost you real voltage drop. Keep it as short as physically possible, use proper lugs crimped correctly, and don't let anyone talk you into anything less than 35mm².

@CopperWelder curious where you were going with that — guessing you were about to mention the inrush/surge current? Yeah that's the killer on 12v systems.

From my own setup (Multiplus 12/1600 on a static cabin) I actually went 50mm² rather than the minimum spec, purely because my cable run is about 2.5m each way. Longer run = more volt drop = more heat = bad times.

Quick rule of thumb I use:

• Under 1m → stick with 35mm²
• 1-3m → seriously consider 50mm²
• Beyond that you're probably better off rethinking your layout

Also worth checking your fuse/ANL sizing at the Lynx end — people obsess over cable gauge then under-fuse or over-fuse and undo all the good work. Victron's wiring unlimited PDF covers this properly if you've not read it.

@DownsExplorer done all this on my narrowboat and the bit nobody mentions is cable length — every extra metre on a 12v system is basically setting your voltage drop on fire whilst laughing at your inverter's efficiency.