Wiring
Bilge Pump Wiring
A float switch runs the bilge pump on its own when water rises, and a 3-way panel switch lets you run it by hand. Here is how both are wired, using the float switch maker's own instructions.
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Disconnect the battery
Turn off every load and remove the battery's negative cable before you touch the wiring. The automatic pump is off too until you reconnect, so do this with the boat out of the water or with someone aboard.
Match the switch to the pump
A float switch carries the pump's full current. Rule rates its Rule-a-Matic at 14 amps and its Super Switch at 20 amps at 12 volts, half that at 24 volts, and says not to use them on a pump that draws more. Read the current off the pump's own label.
Mount the float switch
Rule's instructions put the switch on a flat surface in the bilge, parallel to the waterline, with the wire leaving toward the stern, and 1/4 inch above the bottom of the pump's strainer so the pump shuts off cleanly. Leave the float free to move.
Wire the automatic circuit
Run the battery's positive side to the fuse, the fuse to the float switch, and the switch to the pump. The pump's negative wire goes to the negative bus or the battery's negative. Rule connects the fuse directly to the battery's positive side, so the automatic circuit does not depend on the boat's main battery switch.
Add manual control
A 3-way panel switch with manual, off and auto positions lets you run the pump by hand, which Rule notes will pump the water lower than the float switch turns off at. In Rule's drawing the fuse feeds the panel switch. AUTO powers the float switch, MANUAL powers the pump directly, and a red light on the pump's feed shows when it runs. OFF cuts power to the float switch too, so leave the panel on AUTO.
Size the wire
Use the pump's current draw and the round-trip length in the 3% table of the marine wire gauge chart, and go a size up in an engine space or a bundle of more than three wires. Rule says wire added to the pump's leads should be at least the same gauge up to 20 feet, and one size larger beyond that.
Seal the connections
Keep every connection above the highest water level in the bilge and seal it with marine sealant, as Rule's instructions say. Heat-shrink butt connectors seal the joint itself.
Test it
Reconnect the battery. Lift the float (or press the test lever on switches that have one) and check that the pump runs and stops. Then check the panel's manual position.
Rule float switch ratings
Maximum pump current each switch can carry, from Rule's instruction sheet. All of them switch the pump on at 2 inches of water and off at 3/4 inch.
| Switch | 12 V | 24 V | 32 V |
|---|---|---|---|
| Rule-a-Matic (35A, 35FA) | 14 A | 7 A | Not rated |
| Super Switch (37A, 37FA) and Rule-a-Matic Plus (40A, 40FA) | 20 A | 10 A | 6.5 A |
Wire color
ABYC E-11's color code uses brown for the wire from the fuse or switch to a pump. Matching it makes the circuit easy to trace later.
Common questions
The automatic circuit in Rule's instructions runs from the battery's positive side through a fuse, so it does not depend on the main battery switch. Check your boat builder's wiring diagram for how your boat is set up.
The size the pump maker recommends for that pump. Rule says its float switches must be fused at the pump's recommended size.
Size it from the pump's current and the round-trip length using the 3% table. Rule adds that wire added to the pump's leads should be the same gauge or larger, and one size larger past 20 feet.
Check that the fuse matches the pump maker's rating, clear any debris jamming the pump or the float, and look for corroded or wet connections. Rule says to keep connections above the high-water level and seal them.
A pump with three wires usually has a built-in automatic switch, with separate wires for automatic and manual operation. Follow the pump maker's diagram for which is which.
Sources
Rule's float switch instructions (Xylem form 950-0290); ABYC E-11, AC and DC Electrical Systems on Boats, as excerpted by Paneltronics.