Form factor and what it actually is
Omron's Z-15HQ21-B sits in the Z series of general-purpose basic switches — the classic snap-action limit switch used as a position-trip element on machine gates, conveyor end-stops, and door interlocks where a mechanical cam pushes the actuator and the contact snaps over. The body is a basic-switch form factor: a single-pole/double-throw (SPDT) contact set with screw terminals brought out the side for hard-wiring into a control panel or junction box, and a 4.2 mm mounting hole pattern for panel or bracket fastening.
Headline ratings and what they decide
The 15 A at 250 VAC rating on the SPDT contact set is the figure that decides fit for a 240 V single-phase motor starter aux circuit or a solenoid/valve coil driver — anything drawing more than 15 A continuous belongs on a contactor, not a limit switch. Inrush tolerance is asymmetric: the NC leg handles up to 30 A inrush, while the NO leg is rated for up to 15 A inrush, which matters when switching inductive loads like solenoid valves or motor starter coils where the closing surge runs well above the steady-state current. Mechanical switching is rated at 240 operations per minute maximum, with an electrical endurance floor of 500,000 operations — the mechanical figure is the duty ceiling a cam-driven application must respect, and the electrical figure is the wear budget over service life.
Wiring it in
Screw terminals accept standard stripped conductors and are the wiring side of the switch — the actuator side (lever, plunger, roller) is the part that sees the machine motion, so the panel-side wiring is straightforward but the actuator selection drives the actual trip behaviour. The 4.2 mm mounting holes fix the body to a bracket or panel face; correct mounting orientation keeps the actuator aligned with the cam or striker and avoids side-load that would wear the plunger early.