Blue Sea Systems 400A Class T Fuse – BSS-5121
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400A Class T Fuse for Marine High-Current DC Systems
Maximum-rated overcurrent protection for the heaviest DC loads on board. This 400-amp Class T fuse is designed for main battery cable protection on large powerboats, commercial vessels, and high-capacity electrical systems where no other fuse format is rated for the job. Class T fuses are recognized for their extremely fast-blow characteristics and high interrupt capacity, making them the gold standard for protecting large battery banks and main feed cables.
At 400A, this fuse is purpose-built for the primary connection between your battery bank and your vessel's main distribution system.
Specifications
- Amperage Rating: 400A
- Type: Class T fuse (fast-blow, high interrupt capacity)
- Application: Marine main battery feed and high-current DC protection
- Part Number: BSS-5121
- SKU: BSS-5121
Best Use Cases
- Main battery cable protection on large powerboats and commercial vessels
- Primary overcurrent protection for high-capacity battery banks and inverter systems
- Protecting main feed cables on vessels with large DC loads such as electric drives, thrusters, and windlasses
- Replacement fuse for existing Class T fuse block installations rated at 400A
Parts Desk Insights
The 400A Class T is the highest-rated fuse in this family and is reserved for the largest DC systems — think large inverter banks, electric propulsion feeds, or multi-battery commercial installations. Class T fuses have a much higher interrupt capacity than ANL fuses, making them the preferred choice when fault currents could be extremely high. If your system draws less, see the 250A Class T (BSS-5118) or 150A Class T (BSS-5114). For mid-range main feed protection, the 300A ANL Fuse Block with Cover – BSS-5005 is a cost-effective alternative for systems that don’t require Class T interrupt ratings. Always size your fuse to the wire gauge — not just the load — and consult your system design specs before selecting a Class T fuse.
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 3–4 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.