If it is Self-Regulating Cable, do you need to have a controller?

This depends on the temperature control requirements of the application. If tight, temperature control is required within a few degrees, a line sensing device is recommended.

For freeze protection applications , ambient sensing is commonly used with self-regulating heating cables. The self-regulating effect reduces the resulting equilibrium pipe temperature during operation.

Where the ambient change during the year is small, it may be possible to do a design using a self-regulating heating cable without any controller.