The PE665WGMP0 SurgeArrest surge protector has a 540 joules rating and maximum amperage of 15. The ON/ OFF switch controls the provided power to the surge protector, it also acts like a circuit protector. When an output overload condition occurs the ON/ OFF switch moves to the OFF position. Disconnect all equipment from the SurgeArrest before moving the switch to the ON position. The LED is normally illuminated indicating that the surge protector is on and ready to protect connected equipment. If the LED is not illuminated the surge suppression circuitry has been compromised.