What common polarity means
Direct-coil switches often share one side of several actuator coils at a common terminal. Common polarity identifies whether that shared node is connected to the positive supply or to the negative/return side of the DC supply.
Positive common
With positive (+) common, the positive supply is applied to the common actuator connection and a position is typically selected by switching the appropriate coil lead toward the DC return.
Negative or return common
With negative (-) or return VDC common, the return side is shared and a position is typically selected by applying positive actuator voltage to the desired position lead.
Why the choice matters
The correct polarity depends on the external driver architecture. Low-side transistor drivers naturally complement a positive-common load, while high-side sourcing drivers can complement a return-common load. The exact interface must follow the switch schematic.
When polarity is not required
A separate common-polarity choice is not required when TTL logic is used because internal driver circuitry handles the actuator interface. In addition, some failsafe CEI series do not require a common-polarity selection. The configurator or approved drawing should be treated as authoritative for the selected series and actuator.
Avoiding wiring errors
Never infer common polarity from wire color, connector position or another model. Confirm the part number, schematic, actuator voltage and connector pinout before applying power.
Key takeaway
Common polarity must match the external driver architecture; it is not a separate selection for TTL-controlled configurations.