Transfer switches can be electromechanical or solid state or “static” transfer switches. Here we are focused on electromechanical units.
Transfer switches come in multiple types and configurations. The simplest type is a safety switch, often referred to as a double-throw (DT) safety switch. It is a three-position switch with a center OFF position and two ON positions, each side receiving power from a different supply source. This is a manually opened and manually switched device. There is no separate control scheme. Usually there is no protection involved, although a DT switch can be fusible. This DT switch is one of those we refer to as a manual transfer switch or MTS. Other types of MTS include arrangements with two manually operated circuit breakers or non-automatic switches operated by two concurrent breaker operators and interlocked with a rocking beam interlock. This same arrangement can be electrically operated so that opening and closing can be performed with pushbuttons.