UPB is for single phase 120/240 VAC, 60 Hz systems. The HLC Phase Coupler mounts by the circuit breaker box and is used to connect the signal from L1 to L2 within the circuit breaker box.
A Phase Coupler is a strongly recommended component of an HLC System. Its use increases the reliability of the UPB signal.
The LED on the Phase Coupler shows that it is working.