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Old 15-04-2012, 09:28   #16
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Re: Fuse

My belief is a fuse is meant for protection, mostly against fire or other unnecessary damage an unprotected circuit could cause. If your circuits use heavy gage wires, wires much heavier/larger than actually needed for a normal load you should be aware of what your load requires for protection and not concern yourself with wire protection.

There are many types of load faults that can cause a fire rather than just a circuit interrupt while the wires powering the load remain comfortable with the increased load currents.
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Old 15-04-2012, 11:31   #17
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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
What gauge is the wire. Wire id not labeled by amp capacity but by gauge. Going by ABYC's ampacity cables of 18 awg can handle 20 amps - voltage drop is another issue.

Sounds like very small wire.

Fusing is there to protect the wire. The fuse should be less than the wore's ampacity.
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Old 15-04-2012, 11:51   #18
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Re: Fuse

By the way: Per ABYC E-11; no wire to be used smaller than AWG 16 except for pigtails.

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Old 15-04-2012, 11:57   #19
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Re: Fuse

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Originally Posted by CharlieJ View Post
By the way: Per ABYC E-11; no wire to be used smaller than AWG 16 except for pigtails.

Charlie
Correct. The smallest I use is 14awg.

I am a bit puzzled by the description "15 amp wire."
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Old 15-04-2012, 12:13   #20
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Re: Fuse

Quote:
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
There is no danger using a wire that is too large. It will always be better, other than the slight weight penalty.
However their are 2 considerations with wiring correctly
1. The maximum current capasity of the wire
2. Voltage drop
Both conditions must be met.

Generally for boat wiring 2. Is the limiting factor.
15A wire will often be inadequate for a 5A load because of the voltage drop.
You need to calculate the voltage drop and size the wiring accordingly. It is not unusual to have to use a wire that will ultimately carry 30-40A just to ensure a 5A load does not have excessive voltage drop.
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Old 15-04-2012, 12:20   #21
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Re: Fuse

Ted, you nav lights are probably 10 watt or 20 watt bulbs. If that's a 12 volt system, that would mean a circuit with two bulbs on it (port/starboard) might draw 40 watts, requiring a 5 amp fuse, probably better a 7.5A fuse to allow a little more margin, and still being small enough to protect the wiring. Obvisouly, check your own numbers and wiring before making that choice.

When you switch to LED lighting, you can probably go to one size lower fuse but there's no great reason to, you are still protecting the wiring.
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Old 15-04-2012, 12:36   #22
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Re: Fuse

Standard breaker size in a Blue Seas DC panel is 15 amp. That is an appropriate fuse for any wire used on a boat, which should be 16 awg or larger.

Electronics often has an inline fuse of a smaller size in its pigtail.

I still haven't a clue what gauge 15 amp wire might be.
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Old 15-04-2012, 12:48   #23
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Re: Fuse

"That is an appropriate fuse for any wire used on a boat,"
That's a judgement call. If you know a certain circuit will only be carrying four amps in any normal use, and you fuse it for 15 amps, you are going to allow an 11-amp overload to exist and perhaps to do damage for some time before that 15-amp fuse blows. "Normal" ATC, etc. fuses, after all, do not blow instantly, they are designed to carry an overload for a set time before they blow.

OTOH, if your circuit should never be carrying more than 4 amps, and you fuse it for 5 or 7.5, that fuse will blow faster, and provide a higher degree of protection against melted wires or arced contacts, than a 15-amp fuse will.

15A may be appropriate, but one can often do better than simply meeting a minimum spec.

BS probably ships with 15A since they have to ship with something, and with no telepahtic 8-ball around...sizing for the minimum wire size probably is a reasonable compromise.

The extra inline fuse in the pigtail...I understand why it is there. And sometimes agree with why it is there. And I also remember squeezing halfway into a void on a boat en route to a race to find out why the new fuel gauge wasn't reading...only to find an undocumented pigtail fuse right there, about four feet away from daylight. I hate fuses that are racked up in series that way, even when there's an arguable reason for them.

In household mains wiring, 14AWG wire is often referred to as having a 15A ampacity, as it can carry 15 amps safely day in and day out. Does AWG get used much outside of the US market?
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Old 15-04-2012, 12:58   #24
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Re: Fuse

Awg outside the US? The equivalent would be square mm I think. Or possibly diameter.

Looking at an ampacity chart 18 awg can handle 20 amps - from that I would call "15 amp wire" probably 20 awg, and way too small.

Regarding fuses/breakers, they are there for the wire. the smallest that should be used on a boat is 16 awg which has an ampacity of 25 amps outside engine spaces. 14 awg has an ampacity of 35 amps. 15 amp fuses or breakers would be fine for either as the fuse/breaker should blow or trip long before the wire gets hot.
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Old 15-04-2012, 17:09   #25
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Re: Fuse

Thanks muchly. I think I might change them to LED's then, if I have to climb the mask anyway. Might as well do it now and then I'll know. Cheers. (Hope they havn't used something stupid to run the lights down the mask, like more extention leads or something. grrr)
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Old 15-04-2012, 23:46   #26
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Re: Fuse

The most common way of specifying wire size worldwide is mm squared. AWG is not often quoted outside the USA. You need to be careful that it is mm squared, the size in mm sometimes refers to the diameter, not the cross sectional area.
It's also important to know the current carrying capacity of the wire, this can, occasionally, be the limiting factor for short runs. The specified current carrying capacity generally needs to be de-rated as it assumes a single wire, where in practice is likely to be bundled with other wires and in conduit. High temperatures such as in the engine room also reduce the current carrying capacity.
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Old 16-04-2012, 07:00   #27
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Re: Fuse

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Originally Posted by hellosailor View Post
There are no REQUIREMENTS, which would be statutory and mandatory.
How about Title 33 part 183 (Boats and associated equipment) of the U.S. Code of Federal Regulations? "Each ungrounded current-carrying conductor must be protected by a manually reset, tripfree circuit breaker or fuse."

While the CFR are administrative laws, they are treated by the courts as legally binding statutory laws.

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Old 16-04-2012, 08:15   #28
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Re: Fuse

The guvmint thinks only boats with gas engines are dangerous.

Your quote comes from 183.455. 183.4XX is subpart I. 183.401 is the beginning of subpart I and is concerned with applicability:

183.401 Purpose, applicability, and effective dates.

(a) This subpart applies to all boats that have gasoline engines, except outboard engines, for electrical generation, mechanical power, or propulsion.

From:
Electronic Code of Federal Regulations:



Quote:
Originally Posted by fairbank56 View Post
How about Title 33 part 183 (Boats and associated equipment) of the U.S. Code of Federal Regulations? "Each ungrounded current-carrying conductor must be protected by a manually reset, tripfree circuit breaker or fuse."

While the CFR are administrative laws, they are treated by the courts as legally binding statutory laws.

Eric
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Old 16-04-2012, 09:36   #29
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Re: Fuse

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The guvmint thinks only boats with gas engines are dangerous.
Ah, yes, and I already knew that but had forgotten. I brought this up during an argument about fuel filter heat shield requirements for diesel engines. They brought up the part 183 fuel systems rules and I told them they only applied to gasoline engines. They didn't buy my argument.

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Old 16-04-2012, 10:32   #30
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Re: Fuse

Yes, Eric. But binding on who? Boatbuilders, commercially licensed vessels, or recreational/pleasure boat owners themselves?

Speaking as a recreational boat owner/operator, as most forum members are, and not as a boatbuilder or operator of a commercially licensed vessel....the context is, no requirements. I can wire it up with tinsel and chewing gum, and the CFR doesn't have any say in the matter, does it?

33 CFR 183 refers back to 33 CFR 181, which clearly states it is applicable to MANUFACTURERS. Ain't no one but us chickens in here. We're not governed by 33 CFR 18x, any more than we're governed by the Supreme Soviet.
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