The Allen-Bradley MSR100 is a single-function safety monitoring relay in the Bulletin 440R family, designed for straightforward safety applications where a dedicated, uncomplicated monitoring device is preferred over a configurable safety controller. It monitors emergency stop push-buttons, safety gate interlocks, and four-wire safety mats, providing galvanically isolated safety outputs to interrupt power to the machine's hazardous motion actuators.

Which output configuration suits my application?

The MSR100 is available in three fixed output configurations: 2 N.O., 3 N.O., and 5 N.O. safety outputs. The 3 N.O. variant provides three independent normally-open safety contacts, sufficient for isolating a three-phase motor's control circuit through two contactors (dual-channel architecture) while retaining a third contact for status feedback to a PLC or external indicator. All safety outputs are volt-free, allowing switching of AC or DC load voltages up to the rated contact specifications.

How does reset mode selection affect the safety architecture?

A selector determines whether the MSR100 auto-resets on fault clearance or requires a manual reset pulse. Automatic reset is appropriate for guarded installations where the safety device itself (e.g., a gate interlock) prevents re-access during hazardous motion — the machine restarts without operator intervention once the guard closes. Manual reset is mandatory for perimeter safeguarding applications such as safety mats and light curtains, where a deliberate operator action verifies that the hazardous zone is clear before re-energisation. Wiring the reset circuit incorrectly for the chosen architecture can defeat the safety function; the MSR100 monitors the reset input for plausibility.

What is the migration path for new designs?

A small number of legacy relays in the MSR portfolio are discontinued. Rockwell Automation recommends the Guardmaster GSR (Global Safety Relay) family — particularly the GSR DI, GSR DIS, and GSR SI models — or the Minotaur MSR127/MSR138 series as functional replacements. GSR relays offer the same DIN rail form factor with added benefits: narrower width, plug-in terminal blocks, and built-in diagnostics. Existing MSR100 installations with adequate spare stock can continue to be maintained, but new machine builds should specify the GSR platform to ensure long-term availability and access to current safety certifications.