On rare occasions, the UPB signal strength is not enough to allow for solid transmission throughout the home. In those rare occasions, the installation of this device couples a strong signal from the phase where the UPB transceiver is located onto the weaker phase, thereby improving transmission performance. This device is typically only needed in larger homes. However, due to its low price, it's a low cost factor of safety for increasing the already high reliability of UPB devices. This device wires into the circuit breaker panel (using two circuit breakers), typically being mounted in its own plastic box next to the breaker panel.  This is the more commonly used, standard non-inverting phase coupler.