Bilge pump wiring

Discussion in 'Electrical Systems' started by dereksireci, Aug 9, 2007.

  1. dereksireci
    Joined: Jun 2004
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    dereksireci Senior Member

    In your opinion, what's the best way to wire an automatic bilge pump with an override switch at the helm panel? You must making sure it has overcurrent protection and the float switch will activate the pump even when power to the panel is switched off.
     
  2. USCGRET/E8
    Joined: Jul 2007
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    USCGRET/E8 Senior Chief

    If you have a bilge pump switch with Off /On /Auto
    Wire the auto position to a constant battery power source.
     
  3. dereksireci
    Joined: Jun 2004
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    dereksireci Senior Member

    Thank you for your reply, I had that part figured out already.

    The problem I am describing seems to have worsened lately with the introduction of the high capacity 2000 gph (7570 lph) model bilge pumps which draw higher amperage. The Rule RM 2000 for example is fused at 15 amps. I understand that fuse size is not the amperage the device will draw at locked rotor. Another source of confusion for many is the allowable voltage drop for bilge pumps as dictated by ABYC. Many assume the voltage drop for bilge pumps must be 3%. But per ABYC it can be 10%. No where in E-11 does it specify 3% for bilge pumps. Using 3% is strictly the choice of the builder. One rule of thumb design principle that is often followed is to place the batteries as close as possible to the engines. This allows for smaller gauge engine starting cables. With the high amperage of the bilge pumps however, it may be better to locate the batteries as close as possible to the DC panel.

    Method 1
    Supply power to the float switch with a wire connected directly to the battery or the hot side of the battery selector switch with overcurrent protection provided by an inline fuse within 8” of the battery ring terminal.
    Supply power directly to the pump from the DC panel with overcurrent protection by a breaker on the panel. In this case a diode must be installed to prevent the entire DC panel from being energized when the float switch is closed.

    Scenario: Bilge pump is activated by the float switch. The operator notices abundance of water and activates the bilge pumps manually from the panel. A twig gets stuck in the rotor and causes locked rotor condition. The switch on the DC panel is continuously supplying the pump with power up to the limit of the breaker. Since the float switch is connected to the battery it is continuously supplying the pump with power up to the limit of the in line fuse. Basically the pump is getting twice as much current as it was designed for and may go poof! Hopefully the water in the bilge will put out the fire.

    Method 2
    Supply power to the float switch from the load side of the breaker on the panel. Supply power directly to the pump from a switch on a DC panel connected to the same breaker as the float switch. In the scenario above the pump is overcurrent protected by a single breaker. In this case the bilge circuit on the panel must be isolated from the rest of the DC panel for the float switch to activate the pump when the main switch for the panel is off. The diode is not necessary. The issue here is the length of run to energize the bilge circuit if the batteries are in the stern near the engines.
     
  4. USCGRET/E8
    Joined: Jul 2007
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    USCGRET/E8 Senior Chief

    The wire to the float has to come from the switch. That way the switch will only direct power to one or the other. Guess I should have said "Connect the switch to a constant battery source." I prefer directly to the battery, so there's no way it can be accidently turned off.
     

  5. USCGRET/E8
    Joined: Jul 2007
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    USCGRET/E8 Senior Chief

    The pumps themselves should come with directions dictating wire size and length for min. voltage drop. If you don't have this, you can probably contact the Co. and get it.
     
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