Potential (Magnetic) Relay
Potential relays (relays are used, as a rule, high-torque capacitor-start the engines. They slightly resemble the current relay. However, these relay is based on the increase in voltage. The increase comes as a device approaches and reaches its rated speed. Fig. 8-61 is a potential magnetic switches.
Contact points remain closed during the off part of the cycle. This function is its biggest advantage. If the points are closed because the thermostat closes the electric circuit arc relay points. Arc is quite common with current relay.
Fig. 8-62-connection diagram block with potential relay. As the engine increases the speed, high voltage of primary windings energizes the relay coil, 2 and 5. It opens normally closed contacts, 1 and 2. Starting winding, therefore, threw the chain. Relay coil is connected through the starting winding. Relay coil is made from a wire of small and very small current is passed through it. This minimizes heating winding and core.
The resistance of the relay coil must be high enough to prevent contact points from the opening until the engine reaches 80% to 90% of full speed.
However, this resistance must be low enough to positively open items and remove from circuit winding at the right time. If not, the motor becomes overheated. The relay itself is shown in Figure 8-63. Wiring diagram for its installation is shown in Fig. 8-64.