Q:

What symbol to use for a solid state relay in a schematic?

What symbol should I use to indicate a solid state relay in a schematic?
The internal schematic of the solid state relay is shown in the data sheet, but showing all of the internal components in the schematic is not necessary and would be more confusing than a single symbol.

A:

Use what is in the datasheet. Why? because it matters on what is inside the SSR. Is it optically isolated? Is it simply a mosfet, a triac or back to back mosfets?
With a single block it is impossible to tell. With a diagram inside the component you can tell what it's functionality is, saving some time. 

If you draw what is on the inside and put it in a library its easier for you to tell what it is and use it later on. This of course is all up to you, and it's every person for themselves on this one. If your using it in a group library, then consult your group. 

