Bilge Pump Wiring; 2 Positive Paths OK?

hriehl1 · Post by **hriehl1** » Mon Jun 20, 2011 10:30 am

Below is a proposed wiring diagram for a bilge pump... in essence I want two separate positive paths to the pump:
1. Fused always-on path through a float switch (automatic mode); and
2. Fused SPST panel switch (manual mode).

I know a bilge pump panel switch would be more typical for a similar result, but I have available switch capacity on my main electrical panel I'd rather use (save money and cabin clutter).

The basic question is whether this is unsafe? Both paths would be properly fused. Even if both paths were "hot", the pump will only draw what it is going to draw... right?

Thanks

s/v Faith · Post by **s/v Faith** » Mon Jun 20, 2011 10:55 am

Correct, no problem what so ever.

Your approach is good in that no one can accidentally turn off the 'automatic' operation of the pump.

ILikeRust · Post by **ILikeRust** » Mon Jun 20, 2011 3:43 pm

Good idea, and one I think I will use!

And yes, no problem - if both switches are closed, you've basically got two wires going the same way - it's the same as if you completed the circuit using one wire that is twice the diameter of either of those wires alone. The wire will carry only the voltage that is pushing the current (i.e., you're not going to get more voltage just by using two wires), and the pump will draw only whatever it's going to draw (so you won't get more amperage either). Two wires will offer less resistance than either one alone, but at that level, it won't matter.

mitiempo · Post by **mitiempo** » Tue Jun 21, 2011 12:38 am

Looks fine to me but make sure the manual SPST switch is momentary so it can't be left on.

hriehl1 · Post by **hriehl1** » Tue Jun 21, 2011 8:49 am

Thanks all... In my case, I don't think the manual switch needs to be momentary as the pump makes enough noise in my small cabin that one always knows if the pump is on. I'm also putting a counter in the always-on path to monitor pump activity during the week when the boat is unattended.

The manual switch is simply for convenience to occasionally check that the pump actually works.

mitiempo · Post by **mitiempo** » Tue Jun 21, 2011 11:21 am

Non-momentary bilge pump switches have on many occasions been forgotten and burned pumps out, leading to possible fires. Say if you turn it on and leave the boat for some reason. The price is the same. Best to do it the right way.

I would never wire a customer's pump in such a way that it could be left on as it could lead to burned wires.

Chris Campbell · Post by **Chris Campbell** » Sun Jul 03, 2011 7:55 pm

All the bilge pump manufacturers make switches that work this way - middle is off, pushed one way is automatic, pushed the other way is manual. This way you don't need to wire two separate circuits. The other thing to consider when having two live paths to your pump is that the live one will make the non-live one live, which means that the rest of your electrical system may in fact be on when you want it to be off...

mitiempo · Post by **mitiempo** » Sun Jul 03, 2011 8:14 pm

Actually it won't make the other live except when the pump is activated by the float switch. And it will only be live to the switch which stops the current flow in the manual direction as the manual side is off.

The Rule and Blue Seas bilge pump switches are really SPDT switches like the one below - momentary on one side - but combined with a fuse and sell for $30 to $40 - about 5 times the price of the one shown.

Chris Campbell · Post by **Chris Campbell** » Sun Jul 03, 2011 8:46 pm

The Rule and Blue Seas bilge pump switches are really SPDT switches like the one below - momentary on one side - but combined with a fuse and sell for $30 to $40 - about 5 times the price of the one shown.

Absolutely. And as long as it's wired so that it's switched on the positive on both sides, it should work fine. I was just mentioning that multiple paths for current to flow are sometimes the beginning of rather bewildering electrical surprises. And the "ready made" bilge pump switches have a light to tell you when the automatic switch has turned the pump on, which may be pointless if it's always audible (likely won't be under power), and is easy to imitate with a light on a parallel circuit with a resistor if you want to do it yourself. Oh, and a fuse. And the panel that makes it obvious what the switch is for.

Ultimately, though, it all depends on what the boat wants, though, right?

mitiempo · Post by **mitiempo** » Mon Jul 04, 2011 12:55 am

My main point is that the manual switch for a bilge pump should be momentary so the pump cannot be left on. Whether it is a Rule switch or a switch like I showed there should not be a way to leave a pump on indefinitely in manual mode. Has a lot more to do with safety than what the boat wants.

Chris Campbell · Post by **Chris Campbell** » Mon Jul 04, 2011 8:44 am

Isn't safety the very first thing the boat wants? Followed, in some order according to the boat, by beauty, style, comfort, and speed? I'm referring, of course, to Tim's tag line of "What the boat wants, the boat gets", which I think is a great way to look at boat ownership. There are always going to be tradeoffs of one sort or another, but it's still a wonderful thought.

And I absolutely don't disagree with using the switch you pointed out, I was just pointing out another option which also has merit.

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Bilge Pump Wiring; 2 Positive Paths OK?

Bilge Pump Wiring; 2 Positive Paths OK?

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