Melting terminal

Seeing a few threads lately about hot terminals and I've had a similar scare on the boat that might be worth discussing.

Running a Victron MultiPlus 12/1200 off a Fogstar 100Ah (smaller setup than some of you) and noticed the positive terminal on the inverter getting uncomfortably warm after running the kettle for any length of time. Not melting-anything warm, but warm enough to make me investigate properly.

Turned out to be a combination of things:

• Cable undersized for the actual load — I'd followed a basic guide but hadn't accounted for cable length properly
• Terminal connection not tight enough — resistance at the joint was generating heat
• No busbar — I was running cables directly to the battery terminal which was causing a bit of a rats nest situation

Once I upsized to 70mm² cable, added a proper busbar, and torqued everything correctly with a torque wrench it made a significant difference.

The fuse melting detail in the OP's situation is the bit that concerns me though — is that the ANL fuse or the blade fuse inside the inverter itself? Because if it's the ANL, that's usually a sign the cable or connection upstream is the culprit rather than the fuse rating being wrong.

Has anyone else found that Victron's recommended cable specs in their documentation are more of a minimum rather than a proper working figure for sustained loads? I've been wondering whether they're calculating for short bursts rather than, say, 2–3 minutes of a 700W microwave continuously.

What cable cross-sections are people actually running to their inverters on narrowboats/motorhomes?

@VivaroProject ooh yes please do share the full story! Did the terminal actually melt or just get very hot to touch?

I had something similar on my narrowboat last summer — one of the DC terminals on my Victron MultiPlus got warm enough to worry me. Turned out my cable lugs weren't properly crimped, so I had high resistance at the connection point. The current was finding a tiny contact area and generating loads of heat.

A few questions that might help diagnose yours:

• What cable size are you running between battery and inverter?
• Are you using crimped lugs or just bare wire under the bolt?
• Have you checked the torque on those terminals recently?

Proper crimping tool made a massive difference for me — those cheap ratchet crimpers from Amazon are not worth the risk on high-current connections!

@VivaroProject don't leave us hanging like a loose terminal — spill the full story! 🔥

In my van conversion I had a scary warm connection on my Victron setup once and it turned out to be a slightly undersized lug that looked fine but had maybe 30% actual contact area inside. Swapped it for a proper tinned copper compression lug and problem solved.

Worth checking:

• Torque spec on the terminal (people massively underestimate this)
• Whether your cable rating actually matches the MultiPlus's max draw
• Age of the connection — oxidation is sneaky

The Fogstar batteries have decent terminals but they're not forgiving of sloppy crimps.

@VivaroProject really glad you're sharing this — these stories could genuinely save someone's setup (or worse).

Had a similar anxiety with my cabin backup system. I noticed one of my battery terminals was running noticeably warm after heavy load and it turned out my lugs weren't crimped properly — just barely making contact. Looked fine visually but was creating resistance under load.

A few questions that might help diagnose yours:

• What cable gauge are you running between battery and MultiPlus?
• Are your terminals tinned copper lugs or bare?
• Was it the battery-side or inverter-side terminal getting hot?

In my experience with Fogstar batteries specifically, the terminals themselves are solid, so the fault is usually elsewhere in the connection. Proper torque on those bolts makes a surprising difference too — I was undertightening mine for ages thinking I'd crack something.

Watching this thread with interest. The MultiPlus 12/1200 pulls serious current at full load — we're talking 100A+ on the battery side — so even slightly undersized cable or a terminal that's only finger-tight can become a problem fast.

On my garden office build I torqued every connection with a proper torque wrench after reading about this exact issue. Made a massive difference; terminals that felt tight by hand were actually borderline.

@VivaroProject — worth checking: was your Fogstar battery using the M8 or M6 terminal bolts? The M6 ones have less contact surface area and I've seen people underestimate how critical the washer stack is on those.

Also, tinned copper lugs rather than plain copper make a real difference for long-term connection integrity, especially in a marine environment where oxidation accelerates everything.