Obsolete 4 A fast-blow for 32 VDC rails
The Littelfuse 1206SFF400F/32-2 is a 4 A fast-blow surface-mount fuse from the SFF series, rated for 32 VDC continuous. It clears a 45 A fault at rated voltage — the interrupting capacity is well above a typical 24 VDC control rail short-circuit current, so it safely opens before the board trace vaporises. With a 0.38 melting I²t, this fuse coordinates downstream of a 5 A or higher upstream breaker without nuisance opening during capacitive inrush — the I²t budget is tight enough for 4 A-rated traces.
Sourcing an EOL part
Littelfuse lists the 1206SFF400F/32-2 as obsolete. No official successor order code is recorded — the SFF series itself is the family, and a parametric replacement would need to match the 1206 footprint, 4 A rating, 32 VDC minimum, and fast-blow characteristic.
Approvals and compliance
UL recognized — the approval agency listing means the fuse design has passed UL 248-14 testing for branch-circuit overcurrent protection at the rated 4 A and 32 VDC.