The bus coupler panel joins the two halves of a split busbar. The arrangement consists of two disconnectors with a circuit breaker between them: the upper disconnector faces the first busbar and the lower one the second.
In normal operation the sections are fed separately and the coupler is kept open; when one supply fails the coupler is closed so that the healthy supply carries both sections. This arrangement prevents the whole installation from being lost through a single supply failure.
The disconnectors on either side of the circuit breaker make it possible to isolate the breaker from both busbar voltages at once for maintenance. In a single-disconnector arrangement one side of the breaker would remain live.
Typical use: double busbar distribution substations, industrial facilities requiring uninterrupted supply, and switchyards with two transformers.
