Almost all of the equipment in almost all of the studios is powered by pairs of Furman power conditioners: one of the power conditioners delivers power to the loudspeakers (usually labelled "Loudspeakers"), and the other delivers power to the rest of the equipment (usually labelled as "Main"). These are powered on and off with large switches on the front of the units. A green LED on the front of the unit will light up to indicate that they are receiving and delivering power.
IMPORTANT: Always switch "Main" on first, and then switch on "Loudspeakers." Switch off in the reverse order ("Loudspeakers" first, then "Main"). This is to avoid risking damage to the loudspeakers, which are essential pieces of equipment and which are very expensive to repair and/or replace!