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Old 12-03-2012, 08:25   #1
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Fuse

fuse requirements leading to switch panel, bilge pumps and instruments/guages?
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Old 12-03-2012, 08:28   #2
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Re: fuse

Yes?
depends on the size of the wire?!
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Old 12-03-2012, 08:42   #3
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Re: fuse

Recreational boater? There are no requirements.

One might suggest that every line be fused with a fuse that will blow before the wire itself can start to overload and melt. You need to know the wire gauges. Or, if you know the wires have a higher capacity than the loads they are feeding, you select a fuse that can supply the load--but blow at a slightly higher level.

Numbers begat numbers.
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Old 12-03-2012, 08:46   #4
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Re: fuse

Welcome aboard nekto.eric.
Perhaps some more detail would help us help you in regard to your fuse questions.
For instance, are you asking about fusing the wiring TO the switch panel or say the wiring to the various items (pumps etc).

General rule of fusing is that the fuse protects the wiring, not the equipment so is therefore sized in accordance to the safe current carrying capacity of the WIRE (as Sailmonkey correctly noted).
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Old 12-03-2012, 16:01   #5
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Re: fuse

Quote:
Recreational boater? There are no requirements.
That's a bit cavalier!

In the US, the voluntary standards against which your vessel will be surveyed are produced by the American Boat and Yacht Council. In Europe, they have very similar standards codified in their ISO documents.

As Sailmonkey stated, generally, fuses and circuit breakers are sized to protect the conductors. To expand on this a bit, each conductor has a rated capacity for carrying current. This attribute is known as ampacity. As the conductor size is increased, its ampacity increases. It should be intuitive that an AWG 16 wire can carry far less current than an AWG 1/0 conductor. Fuses and circuit breakers are generally sized to open below the ampacity of the conductor they are protecting.

We really need more info to better answer your question.

Charlie
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Old 12-03-2012, 19:55   #6
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Fusing to protect a wire gauge is only a code of practice. If you want to you can of course fuse lower then that to ensure it blows. Earlier. In my boat most important circuits are on a dedicated breaker sized for the load. The wire is capable f much more.


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Old 12-03-2012, 20:13   #7
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Re: fuse

Fuses can protect the wire or the load. Generally, to protect the wire, the fuse is placed near the power supply and is sized to open when the current exceeds the ampacity of the cable. To protect the load (instrument, or other device) the fuse can be located anywhere along the cable, including inside the device housing and it is sized to prevent serious damage to the device. If one cable is used to supply power to several devices, it should be protected by a fuse, and each device should also be protected by its own fuse.
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Old 14-03-2012, 03:18   #8
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Re: Fuse

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Originally Posted by cantspellwell View Post
hi new here
just read this and there are a few points that i think have been missed
first as has been already said the fuse is to protect the wire only
second the wire feeding your fuse-box from the house battory should be specked for volt drop not maxuim load capacity
in my little 29 footer my fuse box if feed with 16 mm2 that is capable of around 80A and i doubt i could draw 20A with my simple electrial system
i have used the oversized cable so there is minamal volt drop from the battory to the fuse box
and this way the fuse feeding the fuse-box can be at 40, twice the maxium load and 1/2 what the cable can handle
i should never be able to blow this fuse no matter what happens
this means i can't end up with "dead ship" unless i have a good fault in the cable

when the chips are down i still want to be able to use the vhf
Welcome aboard Cantspellwell,
I don't think anyone would disagree with you in saying that the fuse can be spec'd lower that the safe current rating for the wire. This still protects the wiring, jus in a more conservative way.

Look forward to hearing more from you

FWIW, a hand held VHF (or a EPIRB) is a good back up "when the chips are down"
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Old 14-03-2012, 11:51   #9
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Re: Fuse

Charlie-
"In the US, the voluntary standards against which your vessel will be surveyed "
And, who or what requires a recreational vessel to be surveyed in the first place? Answer is, no one, unless you're dealing with an insurer or some other VOLUNTARY contract. I can go buy a boat, any boat, and sail it or drive it for the next 20 years, and there is NO REQUIREMENT as to how I fuse my electrics. ABYC does not apply to me as the owner, although it may apply to the builder. Insurance? I don't have to carry it. There are no state or federal regulations requiring a fuse anyplace on my boat, that's all VOLUNTARY on me, not any kind of requirement. Insurance is voluntary as well, so far. Marinas may require it--but that's another private party contract that doesn't apply to all boaters.

Cavalier? Hell no, simple fact. There are no REQUIREMENTS, which would be statutory and mandatory. Common sense and not wanting to spend time in the burn ward (not a good place to be) dictate the use of fuse, but he asked about requirements.

And you'll note, I did suggest fusing. But as a matter of regulatory compliance? He doesn't need any.
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Old 14-03-2012, 12:01   #10
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Re: Fuse

hellosailor-
Okey dokey!

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Old 15-04-2012, 04:45   #11
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Re: Fuse

Hi all,

Hopefully someone will see this request, seeing it's such an old thread. Can someone tell me. I'm rewiring my boat. I purchased a role of 15 amp twin core marine wire. My question is this. Is there any harm in using too big a wire, if for example something only requires a 5 amp fuse?

Ted
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Old 15-04-2012, 04:58   #12
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Re: Fuse

There's never any harm in over-sizing a wire.
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Old 15-04-2012, 04:59   #13
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Re: Fuse

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Originally Posted by tedsherrin View Post
Hi all,

Hopefully someone will see this request, seeing it's such an old thread. Can someone tell me. I'm rewiring my boat. I purchased a role of 15 amp twin core marine wire. My question is this. Is there any harm in using too big a wire, if for example something only requires a 5 amp fuse?

Ted
No harm at all! In fact it is a good idea. The wire will have lower resistance so there will be less voltage drop in the wire meaning you will be using less amps from your battery bank to power the device. Also means less chance of overloading the wire and causing a fire. Just make sure the fuse you use is rated for the device you are powering. In short when it comes to wiring bigger is better.
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Old 15-04-2012, 06:48   #14
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Re: Fuse

Thanks Capt M, much appreciated. It was only $40 dearer than a 10am, so if that's the case I'll do the whole lot with it. Except of course where I need heavier wire.

Can you also recommend a suitable fuse amp for my navigation lights. The wiring I had on the boat was partially house house wire and other rubbish. Even car trailer wire was used, and a couple of domestic extention cable was used for the bilge and a pump. So, I've just ripped it all out and am replacing it all. For most things I'll just go on what the item (e.g pump, or chartplotter) specs tell me. But i don't know what to use for the nav lights. I'm hoping to replace them with LED's but they are not LED's at the moment.
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Old 15-04-2012, 09:16   #15
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Re: Fuse

Quote:
Originally Posted by tedsherrin View Post
Thanks Capt M, much appreciated. It was only $40 dearer than a 10am, so if that's the case I'll do the whole lot with it. Except of course where I need heavier wire.

Can you also recommend a suitable fuse amp for my navigation lights. The wiring I had on the boat was partially house house wire and other rubbish. Even car trailer wire was used, and a couple of domestic extention cable was used for the bilge and a pump. So, I've just ripped it all out and am replacing it all. For most things I'll just go on what the item (e.g pump, or chartplotter) specs tell me. But i don't know what to use for the nav lights. I'm hoping to replace them with LED's but they are not LED's at the moment.
Very wise to remove that wiring. Sounds like a very YIKES installation by the previous owner. Without knowing the type, number of your lights and how they are wired I really don't feel comfortable with giving a value for the fuse. Best bet is to remove the bulbs and get the number and look up to see how much current they nominally draw. Should be easy enough to find the info on the internet or an auto parts store. Led lights will draw a lot less current and it's a good move to go in that direction when you can you will save a lot of amps.
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