The Siemens 5SP3863-3 is a 3-pole miniature circuit breaker from the SENTRON 5SP3 series, rated at 63 A with an E tripping characteristic and a 25 kA breaking capacity at 400 V AC.
The E tripping characteristic is a less common curve — between C and D in terms of magnetic trip threshold — designed for circuits with moderate inrush, such as certain motor or transformer loads where a C-curve might nuisance-trip but a D-curve would be too slow for cable protection.
The 4.5 width units mean it occupies 4.5 modules of 18 mm each — 81 mm of rail space. The integrated locking slide accepts a padlock, wire seal, or cable ties for lockout/tagout compliance.