Centralized motor thermal memory management

The overload relay units within a motor control group have the timing function for their motor thermal memories under the control of a central controller in communication with the overload relays. Thus expensive timing components and control of timestamps can be removed from individual overload relays. Further reduction of individual overload relay components can be accomplished by removing the nonvolatile memory function from the individual overload relays and allowing the central controller to perform the nonvolatile memory functions for the overload relays. The motor thermal model function for the overload relays can remain in the overload relays or might be moved to the central controller if communication bandwidth permits.