<a href="//commons.wikimedia.org/wiki/Motor_control_centre" title="Motor control centre">Motor control centre</a> base, showing room for expansion in the opening below, that must be <a href="//commons.wikimedia.org/wiki/Firestop" title="Firestop">firestopped</a>. Typically, the hole below the cabinet is the size of the footprint of the cabinet.
<a href="//commons.wikimedia.org/wiki/User:Achim_Hering" title="User:Achim Hering">Achim Hering</a>
CC BY 3.0
<span class="int-own-work" lang="en">Own work</span>