March 24, 2026 • 7 min read
Mercury EP series controllers are powerful, but they have a finite number of inputs and outputs. When you run out of I/O — and on larger installations, you will — the MR16IN and MR16OUT are how you expand.
The MR16IN adds 16 monitored inputs. The MR16OUT adds 16 relay outputs. Both connect to your existing Mercury controller over RS-485 and show up in your access control platform as additional points. No additional licensing. No new controller. Just more I/O.
Use cases: alarm zone monitoring, elevator floor tracking, HVAC status, interlock monitoring for mantraps, auxiliary sensor monitoring.
The MR16OUT-S3 gives you 16 Form C relay outputs, each rated at 5A @ 28 VDC. Every relay is independently programmable for fail-safe or fail-secure. Use cases: elevator floor control, parking gate control, lighting automation, HVAC zone control, lockdown control for multiple doors.
Both modules connect to any Mercury EP series controller (EP1502, LP1502, MP1502, EP2500) via RS-485 shielded twisted pair, up to 4,000 feet from the controller. Up to 32 SIO modules can be multi-dropped on a single RS-485 port. See our Mercury MP1502 guide for more on the head-end controller.