How to Make a Homemade Float Switch

Written by bianca bumpres
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How to Make a Homemade Float Switch
Levels of liquid in fish tanks can be managed using a float switch. (bubbles in tank image by OMKAR A.V from

Float switches are used as kill switches to avoid the overflow of water in a tank. When the water level is too high, the float activates a switch that controls a pump, an indicator or an alarm. Float switches can cost anywhere from £22 to £32. This could be a considerable amount of money to invest every year and a half or so. A homemade float switch can cut these prices in half and produce a sturdy switch at the same time.

Skill level:

Things you need

  • Snap-action switch
  • 354ml. plastic bottle
  • 1-inch or 3/4-inch Tee Slip-Slip-Slip
  • 1/2-inch Sched 40 PVC, 12 inches long
  • 3/4-inch Sched 26 (thin wall) PVC, 7 inches long
  • 3 wire nuts
  • 2 3/4-inch wood screws
  • 1 2-inch pan head wood screw
  • Hacksaw
  • Utility knife
  • Drill

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  1. 1

    Prepare the switch slot. Use the hacksaw to cut the Sched 40 PVC about 5 inches in length. Drill 4 holes right next to each other to create a rough slot to hold the switch.

  2. 2

    Insert the snap-action switch; clean up the slot with a utility knife as necessary to enable a tight fit and avoid having to use adhesive.

  3. 3

    Create the switch hinge. Drill 2 3/16 holes next to each other on both sides of the slotted pipe, which will become the switch arm. Connect the pairs of holes to make oval shapes so that the 2-inch screw can slide back and forth with ease.

  4. 4

    Drill two 3/16 holes on each side of the Tee; these will hold the wood screws for mounting the float switch.

  5. 5

    Drill two 3/8 holes opposite the screw holes for access to the mounting screws. The holes should be big enough to get a screwdriver through.

  1. 1

    Insert the remaining Sched 40 PVC pipe into the top of the plastic bottle; the fit should be quite snug.

  2. 2

    Insert the Sched 26 (3/4-inch) PVC into the bottom of the tee and the other end of the Sched 40 (1/2-inch) PVC pipe into the Sched 26 PVC. The 3/4-inch pipe acts as a sleeve so that the 1/2-inch pipe can slip up and down easily.

  3. 3

    Mount the float switch in your overflow cabinet of choice. Place screws directly over the spot in the water where the switch will be and screw the tee to roof of the cabinet.

  4. 4

    Slide the 5-inch switch arm into the tee until the switch roller is centred lengthwise within the tee. Mount the switch arm into the cabinet roof using the 2-inch screw. Do not overtighten the screw; leave about 3/8 inch of space so that the arm can swing and let the switch close.

  5. 5

    Hook up the hot line from the electrical socket to the switch. See Resources for wiring information and options.

Tips and warnings

  • Use a 7/32 bit round to drill the 4 holes.
  • The snap-action switch wires are coded as follows: black --- common, blue --- normally open, red --- normally closed.

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