Learn how to install a fiber optic termination box step-by-step for FTTH projects. Covers mounting, splicing, routing, labeling, and testing for indoor/outdoor use. What is an FTTH Indoor Fiber Optic Wall Box? An indoor FTTH wall box is a compact, durable enclosure (ABS plastic or. A fiber cable (drop) is run from a nearby terminal that could be either a pole or an underground box) to your home. A small box on the outside of your home called a NID is installed and the fiber is coiled in there and connected to a fiber that runs into the home. If you do not have relevant experience and skills, it is recommended to ask a professional to install it.