As a general rule, if the current flowing through a circuit exceeds 10 amps, it's a good idea to consider using a relay. However, this threshold can vary depending on the specific application and the components involved. In overcurrent, the four most used common types of protection relays are 50, 50N, 51, and 51N. Is a protection relay required in all the electrical panels? If we think that overcurrent can occur any time and damage the electrical. Relay ratings include the coil ratings and contact current ratings. The three main device ratings addressed here are: voltage rating, ampere rating and interrupting rating.