
He is right friend "heater", the specific earth symbol but there are many forms, and that will depend on the designer, a very short example is a switched source, it has 2 sections, hot and cold part, in both they have very different lands, so the put another earth symbol, another example is the diode symbol, there is the rectifier, Zener, tunnel, etc. They are diodes but they represent a unique feature, I don't know if you understand me. Greetings and thanks for your comment, I am pleased that a moderator rectifies me.