Surge protectors are not intended to safeguard against over voltages below the surge protector's maximum continuous operating voltage (MCOV). For a 120V-based surge protector, the MCOV is 150V line to neutral and line to ground. For 480/277Y, the MCOV is 320V line to neutral and line to ground. For 600/347Y, the MCOV is 420V line to neutral and line to ground.