BLT3-400 Class T Fuse Block for High-Current DC Protection
High-current battery systems need more than a properly rated fuse. The fuse block must make a secure connection to large conductors while keeping energized hardware covered.
The OptiFuse BLT3-400 is a Class T fuse block designed for F3T fuses from 225A to 400A. With a 160VDC rating, it is built for demanding battery-powered systems where compact, high-fault-current protection matters.
Key Specs at a Glance
- Compatible fuse: OptiFuse F3T UL Class T, 225A to 400A
- Voltage rating: 160VDC
- Terminals: Tin-plated copper, 5/16″-18 studs accepting M8 ring terminals
- Maximum terminal torque: 107 in-lbs (12.9 N-m)
- Mounting hardware: 1/4″ or M6
- Insulating cover meets ABYC requirements
- Ignition protected to SAE J1171 when an F3T fuse is installed
Why Use Class T Protection?
Large batteries can supply extremely high short-circuit current. When paired with an OptiFuse F3T fuse, the BLT3-400 provides a compact mounting solution for fast-acting, current-limiting protection. The F3T carries a 50kA interrupting rating at 160VDC, helping it safely clear severe DC faults.
The fuse must still be selected according to conductor ampacity and normal load. Inrush and available fault current also affect the final choice. A larger fuse should never be used to compensate for undersized wiring.
Built for High-Current Cable Connections
The BLT3-400 uses a four-stud layout that gives large cable lugs room to connect without crowding the fuse. Breakaway sections in the cover let conductors exit in different directions, making cable routing easier inside battery compartments and electrical enclosures.
This design makes the BLT3-400 a strong fit for marine battery banks and RV inverter feeds. It also suits high-output charging systems or main DC distribution in heavy-duty vehicles.
The open stud layout leaves room for tools during installation. Once the connections are complete, the cover keeps the finished assembly protected without making the fuse difficult to service.
Download the BLT3-400 datasheet or review the BLT3-400 Installation Guide. For help selecting the fuse rating, see our Fuse Selection Guide.
Sebastian Castañeda is a circuit protection specialist and technical writer with application-focused experience in technical support and custom protection design. He contributes practical, application-driven insights to the OptiFuse Blog.