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Hot or Common? Know Before You Wire

Controller Know before you wire
Understanding whether your controller switches the hot leg or the common can save you hours of troubleshooting in the field—and help avoid costly wiring mistakes.

Digital outputs that switch the wrong leg can lead to blown fuses, unresponsive actuators, or confusing diagnostics. Knowing how your controller handles switching helps ensure clean installs and smooth startups.

A few best practices:

  • IO-R switches hot: IO-R modules (e.g., IO-R-16, IO-R-34) use relay outputs labeled HOT and SW—24?VAC goes in on HOT, and the switched power flows out to the load.
  • CIPer switches hot: Honeywell’s CIPer 10/30/50 and Spyder lines typically use triacs that source voltage—expect 24?VAC out when active.
  • Facility Explorer switches common: Johnson Controls’ FX-PCG, PCA, and PCV controllers “switch low”—triac outputs complete the circuit to neutral (COM).
  • Distech does both: Depending on how you wire the COM terminal, Distech ECB, ECL, and ECY controllers can switch either hot or common—just be consistent.

Make it easier on yourself, before landing a wire, check:

  • The datasheet or install guide for DO wiring details
  • Whether the DO is tied to 24 VAC or transformer common
  • The actuator or load voltage expectations
Bottom-line: “Johnson = Joins the Commons, Honeywell = Hits the Hot.”

Everything else either follows one of those two camps or lets you pick via a jumper.

Go deeper: Need quick-reference wiring diagrams or side-by-side controller guides? Reach out to us—we’ve got your back in the field.

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