More questions on electric

[NYSail]

With all this talk of electric wiring, I have been looking closely at my systems....I had an electrician to the boat and he did check my wiring and grounds etc...and indicated all was fine. Also, I have Nigel Calder's Second Edition "Boatowner's Mechanical and Electrical Manual" which is a great resourse for me (love the pictures and diagrams!!).

But when looking at my bilge pump, one wire is connected to the power source with the other wire connected at the ground point on the engine. Shouldn't this wire go back to the dc ground buss in the panel? Seems that is what Calder says or am I misunderstanding something.

Thanks!!

 

[Don S/V ILLusion]

Having multiple ground paths is the single biggest cause of stray current corrosion. Although there are a few examples which make it sometimes difficult, generally, there should be only one common ground ( as Calder describes in more detail in this books).

 

[Ed Schenck]

My main bilge pump is wired the same way. And I would never change that. It is the most fail safe way, solid ground and solid positive. The red goes directly to the house bank. It is a simple standalone system that should always work. Assuming, of course, that the batteries stay up and the float switch and pump are good.

Oh, then there was the time that the hose had failed at the thru-hull behind a panel where I could not see.

 

[NYSail]

In other words, it should be brought back to the common ground bus in the panel, then the panel should come back to the engine ground point.

One thing that also confuses me (with electrical systems that is) is that my bonding system is run with green wires so when people talk of AC ground green wire on the boat, which it is on my ac ground buss in panel, I have to do a double take as my bonding system's green wires are attached to my engine at the dc ground point.

 

[Mike B]

They wire the bilge pump in a fail safe manner. No switches to flip, etc. The Pos is run directly off the battery with only a fuse in the line. The Neg is run directly to a nearby ground. They do that so there's less risk of a failure in the wiring. The more connections you make the more risk you have of one corroding and failing. You certainly do not want a switch in line either as you may forget to turn it on. As I said, as Fail Safe as possible.

As for the AC wiring. Not sure how your boat is wired but some manufacturers seperate the DC from the AC panel to prevent confusion. Either way it's something you'll need to remember, along with disconnecting shore power, before working on or near the AC panel or systems.

 

[Witzend]

Ground loops are a problem, but in this case would only come into effect when the pump is running. Since it should run very infrequently it would have an insignificant effect on corrosion. The biggest culprit for ion depletion is A/C, especially at the slip when your neighbor allows his A/C cable to contact the water.

 

[Don S/V ILLusion]

Ground loops are a problem, but in this case would only come into effect when the pump is running. Since it should run very infrequently it would have an insignificant effect on corrosion. The biggest culprit for ion depletion is A/C, especially at the slip when your neighbor allows his A/C cable to contact the water.

This is the common misconception which causes some to rationalize having multiple ground paths. There will always be difference in potential when multiple ground paths exist regardless of whether any specific circuit is energized. It is that difference which is one of the, if not the single, biggest cause of stray current.
Wiring the positive side of a bilge pump switch direct to the batteries is fine although most people have some auto/manual switch in the line anyway so direct is not always "direct". If you ever notice the effect of stray current corrosion, the most common cause is the bilge switch ground loop.

 

[Stu Jackson]

Multiple ground paths

They could be a problem and they couldn't be a problem.

"It all depends on how it's wired" is a phrase you've heard me use before. An example is NY Sail's green bonding wire: in that case, NYS, LABEL the wire where you can see it and at the ends so you and everyone else will know what it is and not confuse it with the AC green ground.

As far a DC grounds, the originally installed OEM wire sizing in many cases was very poor because when the older boats (and in many cases new boats too!) were built, they were simply NOT designed for the higher electrical loads that people have installed in their boats.

As you all pretty well much know now, the wire sizing includes the length both to and FROM the load, which includes the length of the ground wiring.

IF, I say IF, the ground wiring is of adequate size, the entire grounding "system" should and will be at the same potential. Think of it like the wiring system is a BIG ground bus. Unfortunately, there's usually sections of the (-) system, and it's usually part of the OEM wiring, that is just too small, which sets up an imbalance and "weak point" for lack of a better phrase. This makes sections of the grounding system different than other parts.

So, either rewire and gather your grounds together, or physically trace each of your ground wires and analyze the "system." Simply suggesting that connecting a ground for any device to an electric panel DC ground bus is only part of the equation, since it's quite possible that the ground from the panel to the rest of the boat's DC ground system is too small because it's, remember this ?, OEM wiring!

When I installed our high output alternator we beefed up the charging ground system. I ran my bilge pump (-) to the new beefed up ground NDP, NOT back to the DC panel main negative bus - it was much further away. The size of the electrical loads from our DC panel main (-) bus had also to be analyzed to assure that the loads on the panel did not exceed the voltage drop in the negative bus wiring from the panel to the NDP.

Calder also uses the phrase "Balanced Electrical System." He uses that for sizing the battery system to the loads. It also applies to the wiring.

It all depends on how it's wired.

 

[Mike B]

Don, What don't I understand about your comment? How do you figure the Gnd side of the bilge is going to cause an issue w/corrosion? If the pump is off that means the switch is open and there will be zero, zilch, nada current flow thru the Gnd wire.

 

[Don S/V ILLusion]

Don, What don't I understand about your comment? How do you figure the Gnd side of the bilge is going to cause an issue w/corrosion? If the pump is off that means the switch is open and there will be zero, zilch, nada current flow thru the Gnd wire.

Mike
The pump being not energized is irrelevant - it's on the pos side. The ground circuit is in contact with the engine; the engine with the prop shaft zinc; the battery grnd on the engine block, etc... Each ground is at a different potential. No switches need be operated. The difference in potential between any or all of these grnd paths effectively creates a battery.

Think of it as creating a battery which we all do the minute we put the zinc on the shaft when the anode will sacrifice itself as intended. There is no switch to energize this circuit.

 

[Mike B]

Don, not sure what you mean when you say the pump being not energized is irrelevant - it's on the Pos side. Yes the 12V is on the Pos side but in your previous post you referred to the Gnd side and implied it was part of a ground plane. While the return side is part of the Gnd plane it's nothing more than a bare wire until the pump energizes. Neither the Pos nor Gnd side can impact a thing as long as they're properly wired and the pump is de-energized. Also if the return is on the Gnd side and all of your Gnds are properly tied into the engine then they should all be at the same potential. IMO any differences would be miniscule. I think I understand where you're coming from but not sure I can buy into your theory on this one.
Mike

 

[Ron20324]

Don, I'm with Mike on this one, but we digress from the original question.....

NYS, where do you think the neg buss is grounded? Maybe/probably the engine, but we don't know how your boat is configured. I wonder which "power source" you're connected to. If your power is from the breaker panel, take the ground from there. But if your "power source" is right off the battery (like it should be), then run the grd to the battery neg. Fewer connections mean reliable power, and that's what you want when it comes time for the pump to keep your boat afloat.

 

[Mike B]

Ron, his return (Gnd) for the bilge pump runs back to the Gnd lug on his engine so he's wired as he should be.

NYS as I mentioned in a previous post when it comes to wiring the bilge pump you want the most direct connections to both the DC Pos and Gnd as possible. If they had run the DC Gnd back through the DC panel it would work just fine but there would be added risk of a failure since there would be more connections in the system. Every connection becomes a possible failure point, not something you want in a circuit for such an important piece of equipment as the bilge pump. Additionally bilge pumps circuits always bypass the DC panel to ensure the pump can never be turned off. This goes for both the Pos and Gnd sides, although Gnds are generally not switched.
Mike

 

[Mike B]

NYS one other thing that may confuse you is that many boats have a switch on the panel for the bilge pump. This is simply a parrallel circuit that enables you to run the pump when you choose or need to. This switch and circuit will not prevent the bilge pump from running if the water rises high enough to trip the float switch. It's there for you convenience.
Mike

 

[Ron20324]

Ron, his return (Gnd) for the bilge pump runs back to the Gnd lug on his engine so he's wired as he should be.

I guess that is where opinions come in to play. I, myself, would not ground any fused device to the engine block. Engines are not usualy the cleanest things. I'll use either the battery or the neg buss block. As we agree, fewer connections make a better/dependable circuit, so that's why I'd take both pos and neg wires to the battery on this all-important circuit.

 

[NYSail]

Once again Thanks to all!! My pump is wired directly to the batteries with the exception of the negative ground which is attached to the engine. Also, I am tracing all my green bonding wires and will tag them all at the engine ground connection just so that I know what is what.

Thanks!