13.3.2.1-2 Physical and Functional Interchangeability

If modules are physically interchangeable, they should also be functionally interchangeable to avoid errors in installing the wrong module.

Additional Information:
Functionally interchangeable units of equipment perform the same function. Physically interchangeable units of equipment can fit into the same mounting position or fixture. If two units of equipment are interchangeable functionally, they should also be interchangeable physically. However, if they are not interchangeable functionally, they should not be interchangeable physically. Units of equipment having the same form and function should be interchangeable throughout a system and related systems.