Duplex fuses in circuits?

[Matt Johnson]

Originally Posted by deblen

Yes.
If you want to fool proof it,drill a small hole in the handles & install a cotter (split)pin thru the pos. & corresponding neg. breaker mounted one over the other.Both will flip at same time. / Len

The handles are already pre-drilled. I'll see if Bluesea sells just the connecting bushing or make one.

Matt

[Nicholson58]

Not claiming this is a solution - but. We have been struck by lighting every two years or so. The only electronic items not wrecked by the last hit were wired with air-break dual pole switches near the device. Breaking the + & - both at least partly removes the wires to the device as a souce of field generated power spikes. Just an observation.

[Wotname]

Originally Posted by Great Knots

Hi all. My John Pugh design 26ft steel yacht has 2 fuses in each electric circuit. A typical circuit is as follows:
Battery positive, battery positive selector switch, positive buss, amp meter, fuse, switch, device circuit is for, fuse, negative buss, negative battery selector switch, negative battery terminal.
As you can see, there are 2 battery selector switches (positive and negative HV cables) as well as 2 fuses in each circuit. Is this related to the fact that she is a steel hull boat?

Disregarding the rights and wrongs on whether the negative side of the battery should be connected to the hull, the fact remains that some (many?) recreational steel boats do have the negative side of the battery connected to the hull.

In this case, it is just like your car and if optional equipment is fitted, there are benefits in having both sides of the circuit protected with overload protection (fuses ).

The reason for the fuse, is that if the hull connection from the battery to the hull/engine should fail, either partially or completely, the (say radio's) negative lead , in some cases, could become the new "return path" to the battery from the hull, potentially overloading the wire.

Do many worry about this - No.
Is it best practice - Yes.

[smac999]

Originally Posted by noelex 77

Welcome to the forum.

Dual pole (both positive and negative) switches and circuit breakers are the better way to wire a metal boat. In fact, it is also better for a non metal boat, but is not generally worth the cost/trouble.

Some commercial boats are required to fit duel pole main battery switches even if they are built from fibreglass.

Generally this is done seamlessly with battery switches and circuit breakers that have a single switch, but break both the positive and negative circuit.

This battery switch for example looks, and operates like an ordinary single pole battery switch, but it switches both the positive and negative wires at the same time. It sounds like the person that built the boat could not source this type of switch and has used two single pole units instead. Other than the nuisance I don't see any problem.

so what happens when you select combine?....




fused and switched negs cause a lot of issues. often when a neg is off or blown stuff still works and finds other paths. but works incorrectly.

[Wotname]

Originally Posted by smac999

so what happens when you select combine?....

……...

Pretty obvious really - deep discharge test

Yep, Noelex77 is rarely in error but when he is, it's exciting to be around

[mitiempo]

Originally Posted by funjohnson

The handles are already pre-drilled. I'll see if Bluesea sells just the connecting bushing or make one.

Matt

The double pole breakers are not 2 separate breakers side by side, but a unique double breaker in design. If one side is turned off the other will also turn off even without the connecting piece.

I wouldn't bother on a fiberglass boat. It will be a lot of work and your panel will be twice as large for the same number of circuits.

On a metal boat it is a different story and if I was building I would isolate every circuit's positive and negative including the drive system from the hull.

ABYC doesn't agree with total isolation though.

[mitiempo]

Originally Posted by Albro359

I don't see the need for having fuses/breakers in the negative supply circuits.

I wouldn't install fuses in the negative on any boat. But if you are using a panel with breakers that are also switches and have a metal boat proper double pole breakers make sense. This way when a circuit is off it is truly off and there is no way current can reach the hull in any spot.

[mitiempo]

There are 2 Blue Seas Dual Circuit switches that can be used for positive/negative switching - part # 6010 and 5510E. They do not have the combine position.

[Wotname]

Yep, big difference between the BS 5510e & the 5511e that Noelex 77 unfortunately posted; only one little number different

There but for the grace of God etc.

[Matt Johnson]

Originally Posted by mitiempo

The double pole breakers are not 2 separate breakers side by side, but a unique double breaker in design. If one side is turned off the other will also turn off even without the connecting piece.

OK, say there is a short on the positive side... both pos and neg would flip with a true dual pole. If I just connect two single poles together, the positive would try to flip, but the connection to the second breaker may keep it held on. Am I getting this right?



Matt

[mitiempo]

Originally Posted by funjohnson

OK, say there is a short on the positive side... both pos and neg would flip with a true dual pole. If I just connect two single poles together, the positive would try to flip, but the connection to the second breaker may keep it held on. Am I getting this right?

Matt

Yes, although I have not tried it I think one breaker may keep the other from tripping.

Just noticed you have an aluminum boat - only saw the Sabre before. As aluminum is more likely to have issues with stray current in a short time period my choice would be proper double pole breakers. Dashew recommends this in his Cruising Encyclopedia and he has a great deal of experience with aluminum construction and maintenance.

On the other hand though Alubat (Ovni) and Boreal use single pole breakers and install a corrosion meter instead and they are aluminum.

[Matt Johnson]

We are rewiring the aluminum boat and I guess I'll just stick to single pole and keep a good eye on the corrosion tester.

Matt

[noelex 77]

Originally Posted by Chuck Hawley

It has an "All" position, in yellow, which would directly connect the positive and negative terminals of the battery bank(s) with catastrophic results.

Originally Posted by smac999

so what happens when you select combine?....

Originally Posted by Wotname

Yep, Noelex77 is rarely in error but when he is, it's exciting to be around

One little short circuit by joining the positive and negative battery cables and everyone is on your back .

Yes, sorry, everyone is correct, I should have posed a picture of the Blue Seas 5510E, which is suitable for a dual pole system, not the 5511E .

[noelex 77]

Originally Posted by deblen

There are all kinds of self appointed experts who have read a particular book or three,but nothing beats real world experience.
Once you have had things professionally checked,I believe you can learn how to run wires safely,make good connections,etc if you are so inclined & are willing to study the many good references on how to do the physical part.
Leave the theory to those that have actually been there/done that.

Your choice / Len

The system I have described is not a backyard solution, it is how most of the high end metal boats are professionally wired. It is more expensive and as it is somewhat overkill for a fibreglass boat, it is not commonly used for this hull material. I can understand that this system might sound strange to anyone not commonly dealing with metal boats.

Some fibreglass boats do incorporate parts of system. As Alan has mentioned, Amel and some other up market boats electrically isolate the engine after start. Charter boats in Australia are are required to fit dual pole main battery switches.

[Albro359]

Originally Posted by deblen

OK-Your pos wire to your mast mounted Steaming(Masthead) light chafes & connects to mast.Your mast is now +12V,as is every other piece of metal,including the rudder zincs,since they are all connected to that copper strap on keel bolt.
Will the Masthead light breaker pop? Why? What path does the current take to get from these +12V components,to the battery negative,because that is where the current has to go to make a circuit & blow the breaker/fuse?

Next-What happens if the same short to mast is high resistance,due to passing thru some corrosion or whatever? The resultant voltage on mast,etc. is small,but still a voltage applied to surrounding water.

Maybe I'm missing something? / Cheers/ Len

Good comment Len,
The masts are not connected to the ground on Amel boats.
And modern Amel boats are 24VDC not 12...not that that makes any difference to the discussion at hand, but just for information.
Cheers
Alan