Need to know when a 1/10^th of an inch of rain has fallen?
                         The Jensen Rain Switch will let you know.

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Designed for sewer/storm drain diversion control, the #JIC-RS100-B Rain Switch will detect 1/10^th on an inch of rainfall, which assures the initial run-off will flow to the sewer system. This first run-off is typically high in contaminants and bacteria, therefore needs to flow to the sewer system for proper treatment. Once the first 1/10^th of an inch has fallen, the #JIC-RS100-B will trip a relay. 
The Rain Switch is connected to a diversion system, directing the subsequent run off to the storm drain system. The diversion system typically consists of a butterfly/ball valve adjacent to a clarifier, or sometimes a sump pump is used which controls the flow to the sewer or storm drain. The system design depends on the plumbing arrangement of your drainage system.
Other uses include irrigation control and  retractable roof control.