Blue Sea Systems Class T Fuse Block 225-400A

The Blue Sea Systems Class T Fuse Block is the mount most inverter manufacturers reference for high-speed, high-current circuit protection. Rated to 400A and 160V DC, it's built around large heat-dissipating tin-plated copper mounting blocks and a clear insulating cover that meets ABYC/USCG requirements.

Key features

• 400A maximum, 160V DC maximum
• 3/8"-16 (M10) stud terminals accept ring terminals up to 4/0 AWG
• Clear insulating cover with breakouts for wire access in any direction
• Not ignition protected — see PN 5502100 for the ignition-protected version

This block accepts Blue Sea's 225A, 250A, 300A, 350A, and 400A Class T fuses (PN 5117-5121). It's typically mounted as close as practical to a large battery bank's positive terminal, ahead of an inverter or DC-DC charger, where a fast, high-interrupt-capacity fuse matters most.

Torque the terminal studs to 190 in-lb when landing cable lugs, and always reinstall the insulating cover before energizing the circuit — the exposed terminals on a Class T block carry enough fault current that accidental contact is a genuine hazard.

Most inverter installation manuals call out a specific Class T fuse rating for the main DC feed, so check that recommendation before sizing the fuse for this block rather than relying on wire-ampacity math alone. Mount the block as close to the battery bank as the installation allows, and in a spot that stays accessible for periodic inspection of the terminal connections, since a loose high-current connection is one of the more common causes of nuisance heating in a DC distribution system.