Blue Sea 5121 400A Class T Fuse

Blue Sea 5121 — 400A Class T Fuse (A3T)

400A Class T fuse for large inverter installations — MultiPlus 12/3000, oversized 3000W+ inverter banks, or builds with significant headroom planned for future expansion.

Key Features

• 400A continuous rating — sized for 3500W-4000W inverter installations at 12V
• Class T fuse class — fastest-acting high-current fuse
• A3T form factor — fits Blue Sea 5502100
• 200,000 AIC

Which Fuse Size Do You Need?

Rule of thumb: inverter continuous watts × 1.5 ÷ 12V = minimum fuse amperage. So:

• 2000W inverter → 250A fuse
• 3000W inverter → 375A fuse (use 400A or 300A depending on install margin)
• 3600W+ inverter → 400A fuse

When in doubt, size up. A larger fuse will still protect the cable if properly matched to cable ampacity.

Pairs Well With

• Blue Sea 5502100 Class T Fuse Block
• 3000W+ inverters (Samlex PST-3000 / Xantrex Freedom SW3012)
• Renogy 12V 300Ah Mini Lithium Battery
• Renogy Bus Bar (high-current distribution)

Need help sizing or wiring? Use our Power Calculator to size your battery bank, then the System Build Helper to plan the full install.