Internal lock and external lock for point machines

[asrisaku]

Thanks Peter

My work needs to test function of point machines but I could not understand clearly for internal lock and external lock. However, I found out that internal lock is usually required in Depot area and external lock is often required in mainline..please correct me if I am wrong. Most of the time mainline requires non-trailable points and depot is allowed for trailable points. Am I right?

Below I have a picture for external lock. Please help confirm my thought.

Thanks
Arnut