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Old 30-05-2015, 03:35   #31
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Re: Duplex fuses in circuits?

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Originally Posted by funjohnson View Post
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
I haven't tried it with marine breakers either.
But I have seen many house breakers that were either cotter(split) pinned,or equipped with a clip-on metal joiner.Both sides trip.
So I was "assuming" marines would do same & we all know what can happen when we assume
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Old 30-05-2015, 03:38   #32
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Re: Duplex fuses in circuits?

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Originally Posted by Nicholson58 View Post
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.
Yes. Not guaranteed protection but can't hurt. My opinion-no experience to back it.
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Old 30-05-2015, 04:03   #33
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Re: Duplex fuses in circuits?

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Originally Posted by smac999 View Post




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.
I agree-I have seen it. But it was always due to poor maintenance,or someone added an item that didn't have a breaker/fuse in neg return(incompetent "electrician ,mechanic,etc" )
IMHO breaking the neg return path MAY be good practice on a vessel that is maintained only by electricians,mechanics,etc who are aware & familiar with a dual breaker system.
I don't see the necessity or benefit (outside of Possible increased lightening surge protection).
Personal opinion is that it complicates things on vessel that are worked on by average techs/mechs & the owner. KISS
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Old 30-05-2015, 04:40   #34
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Re: Duplex fuses in circuits?

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Originally Posted by smac999 View Post
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.
I think what you are trying to convey is "not fusing and switching the positive" will cause a lot of issues. Please correct me if I am misunderstanding.

This is not what a dual pole system does. It isolates and fuses the positive wire in the normal way. The extra feature is that the negative, which is normally live all the time, is also switched. So it not live on a device that is off. This will reduce, not increase, the chance of "stuff still working by finding other paths".
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Old 30-05-2015, 04:45   #35
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Re: Duplex fuses in circuits?

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Originally Posted by funjohnson View Post
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
If it were my aluminum boat,that is exactly what I would do also. KISS

Suggestion : Assuming your rudderstock is SS, get a SS bolt welded head down to the top of it,if possible. Welding one to the side would work also,but would be a frig if you ever remove stock.My point in welding,rather than mechanically fastening,is that welded stuff stays connected.
Run a short length of Battery cable from this bolt to a solid hull connection.
This will connect your "electrically floating" rudder & steering gear to bat. neg.,assuming you connect bat neg to hull also.
This keeps rudder at same potential as hull & prop/shaft,& will eliminate electrolysis from stray currents.
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Old 30-05-2015, 04:58   #36
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Re: Duplex fuses in circuits?

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Originally Posted by noelex 77 View Post
I think what you are trying to convey is "not fusing and switching the positive" will cause a lot of issues. Please correct me if I am misunderstanding.

This is not what a dual pole system does. It isolates and fuses the positive wire in the normal way. The extra feature is that the negative, which is normally live all the time, is also switched. So it not live on a device that is off. This will reduce, not increase, the chance of "stuff still working by finding other paths".
Apologies for butting in on your reply to smac999

Who suggested "not fusing and switching the positive" ? or was it a typo?

What smac999 & I are saying is that in a switched neg system,the strong possibility exists that someone will inadvertantly "over ride" the isolation,by installing something that is always neg connected. I have encountered this fairly often. / Len
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Old 30-05-2015, 05:42   #37
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Re: Duplex fuses in circuits?

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Originally Posted by deblen View Post
If it were my aluminum boat,that is exactly what I would do also. KISS

Suggestion : Assuming your rudderstock is SS, get a SS bolt welded head down to the top of it,if possible. Welding one to the side would work also,but would be a frig if you ever remove stock.My point in welding,rather than mechanically fastening,is that welded stuff stays connected.
Run a short length of Battery cable from this bolt to a solid hull connection.
This will connect your "electrically floating" rudder & steering gear to bat. neg.,assuming you connect bat neg to hull also.
This keeps rudder at same potential as hull & prop/shaft,& will eliminate electrolysis from stray currents.

Few aluminium boats have a stainless steel rudder stock. It is much more sensible to have an aluminium rudder stock in an aluminium boat.

If you do have a stainless steel rudder stock you need to be very careful following this advice. Connecting stainless steel to aluminium when they are both sitting in an electrolyte (seawater) with a thick, low resistance cable you have just created a very nice battery.

That does not mean it always wrong. Some Aluminium boats are built organising all the grounds to single point with zinc protection. The subject is complex, but please do not add, or remove wires from an aluminium boat unless you know exactly what you are doing.

The marine aluminium used in boat construction is, on its own, (almost) totally impervious to corrosion by normal seawater. However if you stuff up the electrics corrosion can be very rapid.
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Old 30-05-2015, 05:45   #38
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Re: Duplex fuses in circuits?

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Originally Posted by deblen View Post
Apologies for butting in on your reply to smac999
No problems. It is a forum .

If you have a dual pole battery system installing a device connected with conventional single pole system will not cause any problems, other than that it is one circuit not receiving the protection of the double pole system.

You do need to careful that whoever works on your electrical system is qualified. Removing the isolation from a system directly connected to seawater like the engine could result in a very much reduced level of protection.

Problems can occur in boat wired with a single pole battery system when someone has installed a device that it switched and fused only on the negative side. This is quite different to dual pole battery system. In fact a dual pole battery system provides some protection because a negatively switched and fused circuit can better coexist with dual pole battery system.
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Old 30-05-2015, 06:20   #39
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Re: Duplex fuses in circuits?

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Originally Posted by noelex 77 View Post
Few aluminium boats have a stainless steel rudder stock. It is much more sensible to have an aluminium rudder stock in an aluminium boat.

If you do have a stainless steel rudder stock you need to be very careful following this advice. Connecting stainless steel to aluminium when they are both sitting in an electrolyte (seawater) with a thick, low resistance cable you have just created a very nice battery.

That does not mean it always wrong. Some Aluminium boats are built organising all the grounds to single point with zinc protection. The subject is complex, but please do not add, or remove wires from an aluminium boat unless you know exactly what you are doing.

The marine aluminium used in boat construction is, on its own, (almost) totally impervious to corrosion by normal seawater. However if you stuff up the electrics corrosion can be very rapid.
The purpose of connecting rudderstock to hull with heavy cable is to ensure the rudder never rises above 0 V with respect to the hull,neg bat.,bronze/SS prop & shaft. No voltage difference-no current thru water-no corrosion. / Len
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Old 30-05-2015, 06:35   #40
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Re: Duplex fuses in circuits?

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Originally Posted by coastalexplorer View Post

It would be good if you ran an 8 gauge wire from your neg bat term to a keel bolt. This will connect the negative wiring in your boat to earth,& help eliminate potential corrosion & other problems.
This is a bad advice in my opinion. I am a professional engineer and ABYC-certified marine electrician.

Typically there is a decent electrical connection (at least for DC and 50/60Hz AC) betwen engine and water through the shaft and water intake.

If you add another connection between battery negative and water via the keel or some other point then you will have awful corrosion from two sources: current in the water from leaks in other boats and electrolysis from the two different metals that are underwater and you have now connected.

The green wire between rig and keel is another story. It is likely to help with lightning and will not cause corrosion if the rig is isolated from battery negative despite nav lights and VHF antenna. I have checked a few Beneteaus on this and the rig is perfectly isolated from negative; this explains why there is not much of a corrosion problem in them.






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Old 30-05-2015, 07:09   #41
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Re: Duplex fuses in circuits?

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Originally Posted by noelex 77 View Post
[...] The main gain of a dual pole system is in the reduction of stray current corrosion. Unlike other forms of corrosion, stray current corrosion can be very rapid. This is a much greater risk for a metal boat, although something like a saildrive on a fibreglass boat can be destroyed in a very short time from this type of problem.

[...]

We commonly think of the negative wires sitting at the same potential as each other, but in practice there are voltage differences. Even before any fault has developed wires in a well installed system are sized for 0.2 V drop on each pole. Higher differences are commonly seen.[...]
Got it. Thank you for a clear and thorough explanation.
So it is double _breaker_ that brings the most advantage, not the double fuse.
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Old 30-05-2015, 07:22   #42
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Re: Duplex fuses in circuits?

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Originally Posted by svlamorocha View Post
This is a bad advice in my opinion. I am a professional engineer and ABYC-certified marine electrician.

Typically there is a decent electrical connection (at least for DC and 50/60Hz AC) betwen engine and water through the shaft and water intake.

If you add another connection between battery negative and water via the keel or some other point then you will have awful corrosion from two sources: current in the water from leaks in other boats and electrolysis from the two different metals that are underwater and you have now connected.

The green wire between rig and keel is another story. It is likely to help with lightning and will not cause corrosion if the rig is isolated from battery negative despite nav lights and VHF antenna. I have checked a few Beneteaus on this and the rig is perfectly isolated from negative; this explains why there is not much of a corrosion problem in them.






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Wondered where you have been. Welcome

I have a diploma in Marine Electronic Engineering Technology from what Americans call a college,as opposed to a University,which are the only institutions in Canada that can grant a degree.
I am not an ABYC- certified Marine Electrician,but I have spent over 30yrs as a Marine Electronic & Electrical Tech.,among other electrical & electronic engineering jobs I've held.
I'm also fairly versed in mechanical & hydraulic work-mostly learned the hard way. And I can run a table saw,etc. quite well.

Would you please go back & read all the posts in this thread first.
Please don't say something has to be done a certain way because ABYC says so.That is no help to "skeptics or other less knowledgable" folk.
We want the technical reasons,& with your training & experience,you should be able to explain the logic to us.
The OP asked about dual breakers/fuses in DC.
Though this thread has touched on lightening,isolated vs.un-isolated neg battery & earthing, I think we should(with apologies to OP) limit this thread to DC battery. There are several followers who are admitted non-electrical.

Thanks/ Len
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Old 30-05-2015, 07:23   #43
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Re: Duplex fuses in circuits?

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Originally Posted by deblen View Post
The purpose of connecting rudderstock to hull with heavy cable is to ensure the rudder never rises above 0 V with respect to the hull,neg bat.,bronze/SS prop & shaft.
It does not work like that.

You have two dissimilar metals (stainless steel and aluminium) immersed in an electrolyte (seawater). The stainless steel and aluminium have a different potential and the large heavy gauge wire you are installing will ensure a low resistance connection. The aluminium will corrode.

This is like attaching a zinc to your stainless prop shaft. The physical attachment ensures a low resistance connection (like the large gauge wire) and the zinc corrodes. This happens even if the prop shaft and zinc are connected to the negative battery terminal, as is often the case in fibreglass boats (via the engine). Connecting the negative battery terminal to the propshaft does not stop the zinc working (ie corroding). The only difference with your proposal is that you are substituting the aluminium hull for the zinc.

This sort of attachment is sometimes done if there is carefully thought out zinc protection but this requires expert advice. Simply connecting a stainless steel rudder stock to an aluminium hull is not good advice.
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Old 30-05-2015, 07:29   #44
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Re: Duplex fuses in circuits?

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Originally Posted by noelex 77 View Post

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.


No!!!!!!!!!! :banghead :

Perhaps the "COMBINE" or "DEAD SHORT" position of that switch was missed for switching positive & negative...........


This is the Blue Sea switch you would use to break negative and positive if you desired to. The 5510e has no COMBINE position:





EDIT: Sorry I just re-read this thread and see that this was already addressed. Never hurts to emphasize I guess....
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Old 30-05-2015, 09:13   #45
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Re: Duplex fuses in circuits?

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Originally Posted by Maine Sail View Post
EDIT: Sorry I just re-read this thread and see that this was already addressed. Never hurts to emphasize I guess....
Well, it is nice to see the forum does not allow a mistake to slip through .

Of course it would be nicer if it was not my mistake .
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