In this paper, through the case of the misoperation of the sum current circuit and digging out the cause of the misoperation, it is found that all the malfunctions occur on the terminals, and the traditional terminals have no anti error prevention measures, thus the concept of a new type of anti error terminal is proposed and a new type of terminal, such as current, bus differential protection and joint jump, is developed and applied. In this paper, taking the hidden trouble of sum current circuit as an example, the uniqueness of terminal operation sequence is realized by improving the structure of test terminals used for sum current loop. The lock is realized through the inherent mechanical structure of terminals, and the misoperation accidents in the current loop are completely eliminated. The new anti misoperation terminal prevents the jumping operation, skillfully conceals the places where may be touched by mistake, and subverts the concept of the traditional terminal. It changes the situation that the accident occurred repeatedly by the secondary measures as a single technical management means, which greatly promotes the development of the relay protection secondary technology. The new idea of using the new anti malfunction terminal to solve the malfunction of the loop is created. At the same time, the new terminal can be applied to the circuits of metering, automation, etc., and has wide application scope. This work is supported by Science and Technology Project of China Southern Power Grid (No. GDKJQQ20161128).