Answer: The ellipse represents a coaxial multi-core cable wire!

Note: It means that the same cable wire, which has multiple strands of mutually exclusive cores.

In this picture: the first picture inside the representation is that the same wire inside the three phase wires, two of which are the main current line of the load to do work, generally black (zero) and red (fire) two colors. The other one is the green and yellow ground wire!

The second picture inside the representation of the coaxial two-wire wire, there is no ground wire! It is also known as the "two-phase wire"!

This should make sense! Please adopt the support! Thank you.