FAQ: Normally Open (NO) or Normally Closed (NC) operation
How can I tell if my float switch is set for Normally Open (NO) or Normally Closed (NC) operation? How can I change it from NO to NC (or vice versa)?
The "Normal" position refers to a float switch in an empty tank, before liquid has affected the float. Each style switch is equipped with a means to identify which type of operation to which the float switch is set.
- Vertical: the float's witness mark (stainless steel models) or magnets (plastic models) indicate the NO/NC operation
- NO is indicated by circle up (stainless steel) or magnets down (plastic)
- NC is indicated by circle down (stainless steel) or magnets up (plastic)
- Horizontal: the direction of the arrow on the hex indicates the NO/NC operation
- NO is indicated by arrow up
- NC is indicated by arrow down
Use an ohmmeter or continuity meter to verify the switch setting and operation. For vertical switches, simply connect the meter to the leads and, with the float hanging down away from the fitting, measure the switch. If the meter reads a short, then the switch is normally closed and will open on rise.
Most stock Madison float switches ship in the Normally Closed (NC) position, unless otherwise specified. To change the contact operation for vertical switches, remove the retaining clip and float, and reverse the float on the stem. The only exception to this is the operation of the subminiature switch (M3326/M3326-NO), which must be specified when ordered, since the float is not reversible on this model. For horizontal switches, simply rotate the switch 180° in the tank installation.