Q: What LEDs are Illuminated when the R-3W is Installed on a 240V Split-Phase System?

A: When the R-3W or other Voltage Indicating PESD is wired into a 240VAC Single / Split-Phase 3W + GND System, only the L1 and L2 LEDs illuminate when wiring per the below diagram.  This is because the two hot phases are 180° out of phase so they "balance" due to the design of the Voltage Indicator.    

If a fuse or breaker was blown on L1 or L2, then the L3 (connected to Neutral) and GND LEDs would illuminate.