The ENW21811 is a closing voltage release for the EasyPact NW range of air circuit breakers — the XF variant, fixed-mount version. It sits in the control circuit of the breaker, not the main power path: when its coil sees 100-130 V AC/DC at 50/60 Hz, it allows the breaker to close; drop the control voltage below the 0.85 Un threshold and the release blocks closing. That 4.5 W holding power is what the control transformer or UPS needs to budget per unit.
The 55 ms response time governs how fast the release reacts to a close command — fast enough for standard breaker sequencing, but not a high-speed transfer scheme. The 0.85 to 1.1 Un operating threshold means the release is guaranteed to pick up at 85 % of nominal and must not drop out below 110 %; if your control bus sags below 85 V on a 100 V nominal system, this release won't hold the breaker closed. Fixed-mount only — no drawer-style chassis swap; the release bolts directly into the breaker cradle.