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Old 13-04-2010, 16:58   #1
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Bilge Pump Switch 'Hot' or 'Ground' ?

I put in a float switch the other day. I would have wired the hot lead to the float and then to the pump. But the directions showed it the other way; hot lead to pump with the switch on the ground lead. My thinking was that with the hot going to the switch the pump wasn't always "hot". Either way the switch is still hot on one side all the time. I've since seen a wiring diagram with thr hot going to the switch first the way I was going to do it before I looked at the directions.

So do you think it matters? How did you wire yours?
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Old 13-04-2010, 17:12   #2
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I had no idea how my pumps were wired so I've just checked. The switch is on the hot side. That's how PAE did it and they use American standards.
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Old 13-04-2010, 17:29   #3
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it does matter - you want to avoid accidentally energizing the water in the bilge (leading to stray current corrosion). put the switch on the hot side so that the pump is grounded at all times.
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Old 13-04-2010, 17:42   #4
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Don,

If you REALLY want to be confused, google "conventional versus electron flow"
Hint-- blame it on Ben Franklin.:
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Old 13-04-2010, 18:26   #5
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Don,

If you REALLY want to be confused, google "conventional versus electron flow"
Hint-- blame it on Ben Franklin.:

I'm ex-navy so I know this one.
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Old 13-04-2010, 18:28   #6
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it does matter - you want to avoid accidentally energizing the water in the bilge (leading to stray current corrosion). put the switch on the hot side so that the pump is grounded at all times.

You're going to have to explain who you can "energize" water
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Old 13-04-2010, 18:33   #7
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Quote:
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If you REALLY want to be confused, google "conventional versus electron flow"
Hint-- blame it on Ben Franklin.:
If I remember correctly, electrons barely 'flow'. It can take all day for a typical electron to go the length of the typical wire. Plus, it's the 'holes' that flow conventionally, anyway, but you knew that, right?
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Old 13-04-2010, 18:39   #8
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water's a conductor (at least dirty water is). if a hot source is put in the bilge water, current will flow from that source to ground (or maybe the other way around hey, you learn something new everyday). doesn't really matter which "direction" it's flowing - the point is you don't want the water exposed to +12V since everything else is theoretically grounded (engine block, perhaps the sea cocks, etc.) and the "energized" water will complete that circuit with some pretty nasty results.

nigel calder covers this for a paragraph or two in his book. to be honest, i can't recollect exactly why it's more important for the switch to be on the hot side than the pump since theoretically they're both submerged anyhow... but i do know that's the recommendation.
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Old 13-04-2010, 18:43   #9
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just going to complete the circuit and the pump will come on, unless the motor casing is shorted which wouldn't make difference regardless
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Old 13-04-2010, 18:55   #10
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"completing the circuit" in this case refers to small amounts of current flowing from the bilge pump through water to the seacocks, gas tank, engine block, SSB grounding plate or any other source that's a direct path to ground.

there's not enough current to actually activate the pump and the current isn't traveling across the brushes and the armature (where you'd need it to actually have the pump spin). there could be enough stray current to corrode the ground receptacle though. i'll look through the calder book and see if i can explain it more concisely...
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Old 13-04-2010, 19:01   #11
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from the link below:

"While less common than galvanic corrosion, stray current corrosion is typically swift and deadly. There have been boats that were sunk when someone carelessly left a battery cable dangling in bilge water. All of the underwater fittings (bronze) were pink and nearly crumbling in only a few days. In other cases, crimped wires in the bilge were "leaking" 12-volt current into the bilge water."

basically, the worry is that your pump becomes the battery cable if it's tied directly to the +12V side.

The current scoop on galvanic corrosion - page 3 | Boat/US Magazine
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Old 13-04-2010, 20:01   #12
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First I use an automotive relay to operate the pump, the float switch will last longer. I wire the positive to the relay the negative to the float switch. Now I use recycled washing machine level switches (free) for my tree bilge pumps. Now if the switches where to fail, the sea water will raise to the exposed terminals short circuit the terminals, operate the relays and run the pumps. And bingo double security.
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Old 26-04-2010, 05:39   #13
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Well I got another switch (a Water Witch) to replace the 1 I put in couple weeks ago (a Rule). The Water Witch directions were the oppose of the Rule and said to wire the switch in between the battery and pump. In the end I wired both switches at different levels with the Witch being the first. Wired both switched via fuse directly to battery and wired the main panel breaker as a manual on/off.
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Old 26-04-2010, 08:25   #14
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It doesn’t really make any difference, and the wiring / pump motor / switch should all be sealed and the electrics insulated from water anyway. (Make sure you don’t have any splices or uninsulated electrical connections where the bilge water can get to them.)
However, if you really want to be picky, I would suggest running the +ve to the float switch, because there’s no point having 12 VDC ‘potential’ sitting in both the switch and the pump, as that doubles the chances of the insulation breaking down in one of the components, and subsequently causing some ‘stray current’ leakage into the bilge water.
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Old 26-04-2010, 22:10   #15
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This is a wiring diagram for a Rule float switch...maybe this will help.


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