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Old 02-02-2018, 05:00 PM   #1
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Minimum wire size

If I am not mistaken minimum wire size aboard should be awg18.
Why to have this limitation and not something more flexible relying on common sense?
I want to install a led tube above my galley countertop. The light draw 0.2A and if I follow the rule I will need to use wire that can support up to 20amps, what's the reasoning behind this?

L
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Old 02-02-2018, 05:11 PM   #2
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Not sure exactly what you are saying. 18 gauge will not support 20 amps. If the LED light is 12 volts, it is a case of measuring the total length of the circuit and using a chart that will show what size wire need to be used based on circuit lenght and amp draw and desired voltage drop. Personally I really donít use anything smaller tham 16 gauge. The places I can use a smaller conductor are few so I donít stock smaller wire. It isnít a problem to use larger wire than necessary.
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Old 02-02-2018, 05:18 PM   #3
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Lou, check out the Blue Sea ampacity chart, it will tell you what you require. Free (although Blue Sea gets a good buck for its products).
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Old 02-02-2018, 05:23 PM   #4
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The minimum for electric power (not data) is usually #16, not #18. The reason is not current carrying capacity, it's physical strength.

That said, as the boat's owner, you can use whatever you want to. There are no boat wiring police. Just be sure you have overcurrent protection based on the wire size installed at the source of power.
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Old 02-02-2018, 05:25 PM   #5
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What I mean is what is the need for such size when you draw less than 1 amp? I know that going bigger is not a problem but when you try to do an aesthetic install and to hide the wire, I would prefer to use 22 awg that would be enough on the 3 feet length I need and easier to hide.
I do not understand the reasoning behind a minimal size v.s. simply using a wire that is big enough to support the load?
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Old 02-02-2018, 05:29 PM   #6
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Quote:
Originally Posted by Lou_tribal View Post
What I mean is what is the need for such size when you draw less than 1 amp? I know that going bigger is not a problem but when you try to do an aesthetic install and to hide the wire, I would prefer to use 22 awg that would be enough on the 3 feet length I need and easier to hide.
I do not understand the reasoning behind a minimal size v.s. simply using a wire that is big enough to support the load?
Maybe you missed my post above. Or maybe you ignored it.
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Old 02-02-2018, 05:33 PM   #7
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Quote:
Originally Posted by aboatman View Post
Maybe you missed my post above. Or maybe you ignored it.
I was typing when you posted
If I am right the e-11 state the minimum recommendation.

L
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Old 02-02-2018, 05:36 PM   #8
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Your LED and its 18 gauge wire (more on this below) are protected by a 15 amp breaker more than likely. The wire needs to be big enough or the breaker/fuse small enough so that the breaker/fuse trips if the wire shorts to ground due to chafe or whatever. If the breaker is too big or the wire is too small, the breaker will not trip and the shorted wire could cause a fire.

18 gauge is nominally good for 20 amps so it will trip a 15 amp breaker if it shorts. I say nominally because the current carrying capacity also called ampacity is also dependent on its environment. A hot engine room environment results in lower safe current carrying capability.

If you want to use smaller than 18 gauge wire you can; just put a smaller fuse, say 5 amps where the small wire connects to the bigger supply wire or breaker.

Marinco and others have ampacity tables giving safe current carrying capability at different environment temps.

And finally ampacity is the minimum size wire to use in a circuit supplied by a certain fuse or breaker size. The other issue in sizing wire is the voltage drop. But your LED light probably draws less than an amp and that will result in minimal voltage drop.

And finally, finally- what are you tying this 18 gauge wire into on the supply side?

David
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Old 02-02-2018, 06:16 PM   #9
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Originally Posted by djmarchand View Post
Your LED and its 18 gauge wire (more on this below) are protected by a 15 amp breaker more than likely. The wire needs to be big enough or the breaker/fuse small enough so that the breaker/fuse trips if the wire shorts to ground due to chafe or whatever. If the breaker is too big or the wire is too small, the breaker will not trip and the shorted wire could cause a fire.

18 gauge is nominally good for 20 amps so it will trip a 15 amp breaker if it shorts. I say nominally because the current carrying capacity also called ampacity is also dependent on its environment. A hot engine room environment results in lower safe current carrying capability.

If you want to use smaller than 18 gauge wire you can; just put a smaller fuse, say 5 amps where the small wire connects to the bigger supply wire or breaker.

Marinco and others have ampacity tables giving safe current carrying capability at different environment temps.

And finally ampacity is the minimum size wire to use in a circuit supplied by a certain fuse or breaker size. The other issue in sizing wire is the voltage drop. But your LED light probably draws less than an amp and that will result in minimal voltage drop.

And finally, finally- what are you tying this 18 gauge wire into on the supply side?

David
To clarify, I want to install two led lights in a mahogany frame over my countertop. The wire will run from each light on 2 to 3 feet to the main light commands where it will connect to a 1 amp fuse and the switch ( each light is 2w so 0.16A in 12V ). I want to hide the wire in a nice mahogany rail so it does not show, so smaller is easier on the wire size. I know I can use the size I want but if I want to be compliant, if I am right, I need to use 18awg wire, which in my sense is overkill for the very small draw. The main light switches panel is powered by a 12awg (14 would be enough but 12 gives me more flexibility if one day I want become crazy about lightning lol) wire connected to a 10amp breaker on the distribution panel.
Ok I may be too anal on compliance but I want to do it right

L
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Old 02-02-2018, 06:16 PM   #10
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Originally Posted by Xsbank View Post
Lou, check out the Blue Sea ampacity chart, it will tell you what you require. Free (although Blue Sea gets a good buck for its products).
Thank you, their poster wit wire and fuse size is very useful.

L
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Old 02-02-2018, 06:28 PM   #11
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16 gauge is the minimum like ab said
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Old 02-02-2018, 06:35 PM   #12
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16 gauge is the minimum like ab said
What reinforces even more my point .
Or I am just becoming too old and grumpy lol

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Old 02-02-2018, 07:11 PM   #13
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Never too old but definitely grumpy.

Stick whatever wire you want in there, you are the only one who will know.
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Old 02-02-2018, 07:13 PM   #14
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Originally Posted by Xsbank View Post
Never too old but definitely grumpy.

Stick whatever wire you want in there, you are the only one who will know.
Thank you very much I always like when you comfort me lol

L
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Old 02-02-2018, 08:49 PM   #15
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Well, in this case I agree. With a 1 amp fuse protecting the wire, you can use just about anything you want to use, even 22 gauge.

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Old 02-02-2018, 08:55 PM   #16
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Always glad to be a comfort Lou!
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Old 02-03-2018, 09:22 AM   #17
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I think maybe the confusion is the distinction between distribution wiring size (which is 16 AWG minimum) and device wiring size (no minimum?).
Once you have landed the boat distribution wire to a terminal strip, etc, then it turns into a device wire. Lots of device wiring is less than 16. But, that is why it is usually protected by these flying fuse assemblies. VHF, chartplotter, etc.
So, if you have that lower Amp fuse close to the #16, you should be fine. If you are wiring a lamp, for instance that does not come with a flying fuse, then one should be added. I've made this a bit oversimplified, breakers can be used, and fuses don't need to be "flying", etc.
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Old 02-03-2018, 09:29 AM   #18
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Originally Posted by diver dave View Post
I think maybe the confusion is the distinction between distribution wiring size (which is 16 AWG minimum) and device wiring size (no minimum?).
Once you have landed the boat distribution wire to a terminal strip, etc, then it turns into a device wire. Lots of device wiring is less than 16. But, that is why it is usually protected by these flying fuse assemblies. VHF, chartplotter, etc.
So, if you have that lower Amp fuse close to the #16, you should be fine. If you are wiring a lamp, for instance that does not come with a flying fuse, then one should be added. I've made this a bit oversimplified, breakers can be used, and fuses don't need to be "flying", etc.
Ok I may have misunderstood what I read. I thought the min wire size only exception was electronic devices (radio etc) and internal appliance wiring.

Thank you for the clarification!

L
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Old 02-03-2018, 09:51 AM   #19
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I should use the terminology used by ABYC:

k. Pigtails - External conductors that originate within an electrical component or appliance installed
by their manufacturer.

and:

h. Pigtails - Pigtails less than 7 inches in length are exempt from overcurrent protection requirements.

SO, if over 7", then that's where the flying fuse comes in.
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Old 02-03-2018, 01:35 PM   #20
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Yep, if you run skinny leads, protect it with a low amp breaker like 1amp or 3amp. That meets the intent of the rules while maybe not the literal reading. If you are feeding the circuit from a higher amp breaker, then put an in line 1amp fuse in the line to your LED's.
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