What it is — an ABB contactor / starter accessory
The ABB 1SAM451000R1018 is filed on the Contactor & Starter Accessories & Parts line under Contactors and Starters, which itself sits inside the broader Circuit Breakers, Fuses & Protection family — so it is a companion or module for an ABB motor-starting / contactor assembly rather than a standalone breaker or contactor body. The order code is 1SAM451000R1018 and the brand is ABB.
Where the class is used — what this kind of accessory does in a panel
Contactor & starter accessories in this ABB family typically provide the auxiliary, signalling, or interface functions that hang off a motor starter — busbar links, connection sets, terminal extensions, and similar mounting or wiring aids that complete a starter assembly inside a control panel. Sourcing-side, that means the buyer is usually specifying this code to mate with a particular ABB starter or contactor frame; the accessory's role is mechanical or electrical integration rather than switching a load itself.