Correct wiring to prevent Bilge Pump corrosion

[Peter McNamara]

About every 5 years or so I am faced with replacing my 12v bilge pump on my 40ft fiberglass yacht because the seals around the SS pump shaft have apparently failed allowing bilge water ingress and resultant internal corrosion. I am wondering if the recommended method of wiring the float switch as positive supply to the pump is to blame or just the cheap chinese 2000 gph pumps I buy from eBay.

In brief I am wondering, since electrons actually flow from negative to positive side of a circuit, if the float switch circuit can be the negative supply to the pump meaning the circuit through the pump would not be energised unless the float switch was activated, thereby reducing the likelihood of electrically enhanced corrosion as the pump sits soaking in briney bilge water.

I would be grateful for any thoughts particularly from any fellow sailors who have had similar experience or an electrical background.

Thank you

[GILow]

What you describe doesn’t tally with galvanic corrosion to me. There should be no electrical potential between the pump and the bilge water, regardless of polarity of the switched circuit.

I think the cheap pumps are more likely to blame, though I find the Rule pumps aren’t good for much more than five or so years either, and they are not the cheapest on the market.

[RaymondR]

It was a problem with DC submersible pumps even before cheap Chinese pumps became available.

If you suspect it is stray currents switch with a double pole relay so that both positive and negative are both disconnected when the pump is not running.