What amp Class T fuse do I need for a 400Ah lithium battery bank in my van?

Answered by RV Parts Giant · Upland, CA · September 30, 2026

Short answer: Size its amps to the main battery cable, not to the bank. The Class T has to sit above everything that cable carries at once, with margin, and at or below the cable's own rating. On a 12V van with a 3,000W inverter that is roughly 250A of inverter draw alone. Its interrupt rating, 20,000A or more, is what handles a 400Ah bank's short-circuit current.

A Class T fuse has two ratings, and a 400 amp-hour bank decides only one of them. The amp-hours do not set the amp rating at all.

The interrupt rating: set by the bank

Lithium cells have very low internal resistance. A 400 amp-hour bank, whether one battery or four 100 amp-hour batteries in parallel, can push well over ten thousand amps into a dead short. Victron's wiring guide requires at least one fuse whose interrupt rating is at or above the bank's prospective short-circuit current. Class T is rated 20,000A at 125V DC, and Bussmann's JJN series 200,000A. That is why it is the main fuse. An ANL (6,000A) is the wrong fuse at the battery, and a single MRBF (10,000A at 14V) is marginal at this bank size. Check the short-circuit figure on your battery's datasheet against the fuse you buy.

The amp rating: set by the main cable

The Class T protects the cable from the battery positive to your distributor, so size it to that cable. It carries everything at once: the inverter-charger plus every DC branch running at the same moment. The rule has two sides:

Above the continuous draw, with margin, so it does not blow in normal use.
At or below what the main cable is rated for, so the cable cannot overheat first.

A 12V 3,000W inverter such as the MultiPlus-II pulls roughly 250A at full output, before any DC loads. Victron's cable table, for a run up to 5 metres total (positive plus negative added together), rates 95 mm² (3/0 AWG) at 285A and 120 mm² (4/0 AWG) at 360A. So your Class T sits between your real total draw and your main cable's rating. If those two numbers are too close for a margin, the cable is too small or the run too long; move the bank and inverter closer or go up a cable size before you choose the fuse.

Where it goes and what sits behind it

Mount the Class T as close to the battery positive as the hardware allows, before any busbar. The Lynx Class-T Power In holds one Class T per battery input and bolts to the rest of a Lynx system. Behind it, the Lynx Distributor takes a MEGA fuse per branch, each sized to its own cable. The inverter's DC fuse is the one its manual specifies, in the distributor slot feeding it. In a smaller build a six-way MEGA holder does the distributor's job.

Do not pick the Class T from the inverter's wattage alone, and do not skip it because the inverter has its own fuse; nothing else protects the battery-to-busbar run.

We do not currently stock the Class T fuse itself, only the Lynx Class-T Power In that holds it. Send us your bank, inverter and cable runs and we will list every fuse. Everything ships from Upland, California.