The TX3-8EC NSL 8 Relay Expander Cabinet/TX3-16EC NSL 16 Relay Expander Cabinet provide expansion for the TX3-NSL-8M Master NSL Relay Cabinet. The expander cabinets are interconnected to the TX3-NSL-8M via two cables and provide capacity for an additional 8 or 16 Telephone Line Relay Cards. A total of 16 backplanes may be installed for a total of 1,536 Residents.