For triac couplers, how should a VDRM (400V, 600V, 800V) be selected?

Considering AC power supply peak values and voltage fluctuations, generally, Toshiba recommends triac couplers with a VDRM of 400V for 100 to 120VAC load applications, and triac couplers with a VDRM of 600V or 800V for 200 to 240VAC load applications. For triac couplers, an AC power supply voltage is directly applied between output terminals T1 and T2. Although a distance between the output terminals needs to be secured depending on the AC power supply voltage or usage environment, according to the requirement for that distance between the output terminals, a package can also be selected between general-purpose DIP6 and small SO6.