How to Install a Rain Sensor in 7 Steps

lawn in the sun getting heavily watered
  • 2 hours
  • Beginner
  • 100
What You'll Need
Power drill and bits
Masonry fasteners (optional)
Wire cutters/strippers (optional)

If you've ever seen sprinklers on while it's raining, you know how ridiculous it is. (Yes, sometimes we can be judgmental like that.) Not only is it a waste of water, it's also wasting your hard earned dollars.

While it seems easy enough to look out a window to see if it's raining, your automatic sprinkler system can't make that distinction. Enter the sensible and affordable rain sensor. Add one of these to your sprinkler system to save precious resources while mother nature waters the lawn for you.

Step 1 - Choose Your Rain Sensor

Rain sensor technology has changed over the years. Previously, models sported a simple catch basin that triggered a switch once it collected a specific amount of rainfall. This type isn't foolproof unfortunately since debris could also collect in the basin, closing the circuit and prematurely shutting off the system.

Browse rain sensors on Amazon.

The next generation of sensors used electrodes in the bottom of the basin that would close the circuit when enough water filled it, but again it could not deter debris from displacing enough water before triggering the switch to shut it off.

These days sensors have greatly improved, utilizing hygroscopic disks which reduce inaccuracies due to debris being caught in the catch basin. The disks absorb water and swell to shut off the switch to the sprinkler system.

electronic rain drop sensor

Step 2 - Evaluate Placement

An open space where the sensor can take an accurate measurement of rainfall without obstruction from overhanging tree limbs or buildings is ideal. Prune trees that may impede accurate measurements.

Placement must be with respect to location relevant to the sprinkler controls for any connecting wires or wireless transmission. Keep the sensor away from water spouts or sprinklers that could spray water on it and activate its shut-off feature.

Step 3 - Assemble Components

Assemble the sensor according to manufacturer instructions. Depending on the type of sensor purchased, you may need to attach wires to the body of the rain sensor or directly to the sensor pads. There should be a narrow strip between the two sensing components that connects when enough rain fills the sensor.

One of the wires will lead to the indicator to operate the sensor and the other will need to lead to the battery. Another wire must be attached to the other side of the indicator. Use waterproof connectors, referring to instructions to determine if it should be wired in the "normally open" or "normally closed" position.

Step 4 - Wiring Your Sensor

Once the components are assembled, connect it to the power source. If your model has a closed wiring system, most of it is completed at the factory. All you have to do is plug in the wire assembly to the controller to make the sensor work.

If your sensor has an open wiring system, you will need to cut and hard wire your system into your home’s electrical system by hand. If you select this option, make sure that you follow your local building codes for electrical systems.

small circular lawn sprinkler

Step 5 - Set the Rain Sensor

The amount of rain that engages the sensor may require some fine tuning during the season to discover the ideal settings. Generally you can choose between 1/8 and ¾-inch. Select a setting between 1/8 and ¼-inch if you live in an area that is very dry, gets a lot of direct sun or has clay-based soils. On the other hand, if you live in an area that has high humidity, is normally very shady or has a sand-based soil, set your sensor at between ½ and ¾-inch.

Step 6 - Set the Rain Sensor’s Vent Ring

Control how fast disks or basin dries before the system resumes regular operations by making adjustments to the vent ring. If you live in an area of high humidity, open the vent ring up a lot to ensure it dries quicker. An area with low humidity, can keep the vent ring lower.

Step 7 - Mount Sensor

Use the provided brackets to attach the sensor in the desired location.You may need mounting fasteners if you're attaching it to concrete or brick. Ensure the entire unit is upright and level. It's not necessary to angle it to the prevailing winds since the design is meant to catch rain from all directions, as long as it's placed properly. Position the bracket within 25 feet of your control unit, and use the fasteners that come with your sensor to attach the unit to the mounting bracket.

Now you won't be the one watering the lawn when it rains!

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