Wiring diagram for Train Reversing Loop, The rails on the looped section are isolated from the lead out rails at the heel end of the point, the polarity of the rails on the loop is controlled by a DPDT (double pole double throw) switch. This switch can be operated manually or can be controlled automatically using the auxiliary switch on a point motor, most solenoid types have one SPDT (Single Pole Double Throw) auxiliary switch to operate a relay. The relay is then used to switch the polarity of the loop to match the position of the point. Some point motors are equipped with two SPDT auxiliary switches (EG: Tortoise slow motion switch machines) which can be used to directly control the polarity of the loop rails to match the route the point is set to without the need for a relay. By using a multipole relay electrical signalling and interlocking can also be incorporated as required.