Lighting controls like the system at the school usually operate using 12-24v while the lights themselves use 277v(US) or 347v(canada). It's safe to work on the low voltage controls without shutting anything off. If the electrician bothers shutting off the controls at all, it's to prevent damaging components while making connections.
PurveyorOfUselesFact t1_j5aeh0p wrote
Reply to comment by IWankToTits in The Lights Have Been On At a Massachusetts School For Over a Year Because No One Can Turn Them Off by AStartIsBorn
Lighting controls like the system at the school usually operate using 12-24v while the lights themselves use 277v(US) or 347v(canada). It's safe to work on the low voltage controls without shutting anything off. If the electrician bothers shutting off the controls at all, it's to prevent damaging components while making connections.