# question

## Victron multiplus inverter charger 12/3000/120 battery cable size

Hi what size in mm battery cables and fuse do I need to use for a victron multiplus inverter charger 12/3000/120. The manual states 2 x 50mm which refers to 2 x negative and 2 x positive what is the cable size required if only 1 x negative and positive battery cables are being used over a 3 metre run from inverter to batteries. Thanks

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@LesRollins, oooof that's a long run for the batteries to the Multi... being DC, you have to calculate round-trip, so your 3m run is actually a 6m run for your calculations, which leaves 4/0 as the absolute minimum you can safely use (still leaving you at a 2.51% voltage loss over the run). The only alternative, considering ease of running your cables, is to double up with (2) 2/0 cables each for POS and NEG... sadly, there's just no way around that. Anything less and you're running the risk of, at worst, melting your cables and blowing your fuses, or at best, experiencing noticeably poor performance from your Multi because you're getting so much voltage drop between it and the batteries over that run.

No chance of relocating the Multi to be closer to your battery bank?

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Hi Les,

I would think 100mmsq would be right.

But you might not find that size cable/crimps/crimper locally?

Any time I look for cable sizing, I look at this website, https://www.calculator.net/voltage-drop-calculator.html It has a nice cable sizing table half way down.

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so why do they refer to 2 x 50mm negative and 2 x 50mm positive. Does that mean 2 x each cables coming out of the inverter charger but only going on either 1 pole negative and positive of the battery.

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I would think they specify 2 x cables as >70mm2 cable gets very awkward to deal with - make, fit and route. The Multiplus has dual connections ready for a pair of cables.

FWIW, I'm using a single 70mm2 cable for my approx 1M run from Multiplus to Battery Bank (via Shunt and isolation switch to Lynx Distributor). Even that does get a little warm when pulling 200A for over 5 minutes.

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This. I routed 4/0 AWG (=120mm2) from battery to multiplus and it was... an interesting experience. Electrically, you can use 2x 50mm2 or 1x 100mm2. Using 2x may help with routing and bending radius. You do want to make sure that 2x are crimped properly to limit the risk of only having 1x 50mm2 cable actually being used.

w.r.t. fusing, see

https://community.victronenergy.com/questions/22832/correct-way-to-fuse-parallel-conductors-with-quatt.html

There's two school of thoughts - separate fuse for each conductor vs single fuse for both conductors (on the +ve side). Mandated requirements in your area may force choice.

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And thus the reason setting up a 24volt system over a 12volt system is a better idea. Smaller cables due to lower amperage. 2x 50mm2 (1/0)=100mm2. The closest to 100mm2 in the USA is 4/0 cable which is 120mm2.

Yes you do need to fuse each cable or bring the cable lugs together and use one fuse if you can find a fuse holder that will fit that.

I would advise using the Multiplus 24/3000-70/50 120 volt and wire your batteries for 24 volt, wire your PVs to 24-36 volts and use a 24-12VDC converter for your 12 volt appliances. The converter is about \$40 for a 40 amp unit. If you need a 13.8 VDC output the Victron Orion has many options. This way you can use have the cost in battery cable and use one 50mm2 1/0 cable.

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Unfortunately I find the victron manuals and explanations pretty vague for newbies.

As a narrowboat liveaboard I'm off grid with the occasional genny running through a 16 amp shoreline the rest is 960w solars but know the dark nights are drawing in they are becoming less efficient. Perhaps the cables in the manual refer to a set up in its highest capacity

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Well you do need to size your cables based on the output of the Inverter as well as size of your battery bank. You can also downsize the inverter.

The last thing you want to happen on your boat while asleep is a fire from an undersized battery cable. Stepping up to a 24 volt system increases inverter efficiency as well as lowers the amps. When you wire your solar to 36 volts or higher you will squeeze out more charging on overcast low sun days.

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