Surge protection for 486V rails
The 1.5SMC540CA: With a 486V reverse standoff voltage and a minimum breakdown voltage of 513V, it protects 480V-class DC buses or AC rectified rails from transient overvoltage events. The clamping voltage at 2A peak pulse current is 740V maximum, meaning the protected rail sees no more than 740V during a surge event before the TVS conducts and shunts the energy. This is the figure that matters for downstream component voltage ratings.
Power line protection is not provided — this is a signal or DC bus protector, not an AC mains suppressor.