How Do I Add External Limit Switches to a PA Controller?
External limit switches let you stop actuator travel at a custom position in your application — independent of the actuator's internal end-stops. Useful for custom-stroke applications, over-travel protection, or dual-direction stops at user-defined positions.
Internal vs External Limit Switches
| Type | Location | Stops At | Adjustable? |
|---|---|---|---|
| Internal (built-in) | Inside actuator body | Physical end of stroke | No (fixed at factory) or Yes (PA-17) |
| External (application) | Mounted on structure | Custom position you define | Yes — reposition as needed |
Wiring External Limit Switches
External limit switches are wired in series with the actuator's motor circuit — one switch in the extend direction circuit, one in the retract direction circuit.
1. Select NC-type micro-switches
Use Normally Closed (NC) switches. In this configuration, the circuit is complete (motor runs) until the switch is triggered. This is the fail-safe approach — a broken switch wire will stop the motor rather than cause runaway travel.
2. Insert extend limit in positive extend output
Cut the positive wire going from the controller's extend output to the actuator's motor + terminal. Insert the extend limit switch in series: controller extend + → switch NC terminals → actuator motor +.
3. Insert retract limit in positive retract output
Similarly, insert the retract limit switch in series with the retract direction power path.
4. Mount switches at desired stop positions
Mount each switch on your application structure so the actuator mechanism physically contacts and trips the switch lever at the exact position you want motion to stop.
5. Test stop and restart behaviour
Drive to the limit position — the actuator should stop. Verify that driving in the opposite direction works normally (the other direction's circuit is unaffected by a tripped extend switch).
💡 Directional isolation Wiring one switch only in the extend circuit means the extend limit switch cannot block retract motion — the actuator can always retreat to safety even when the extend limit is tripped. This bidirectional independence is a safety feature.