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Old 01-08-2014, 11:32   #16
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Re: LED wire size

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Originally Posted by Terra Nova View Post
I'm no expert on ants and elephants, but I think it's easy to guess which one will make the biggest mess.

On one end of the spectrum would be a wire so fine that it cannot carry its own weight. While on the other end is a wire so stout that it supports itself.
If hung from only it's own weight a large enough wire cannot even support it's own weight, but a very small one can support many times it's own weight.
I'm not an Engineer and don't know how to prove this, but in scaling up, you don't increase the strength of something proportional to it's size, there is a limit as to how big a fiberglass boat can be built for example, eventually the hull would get so thick that it wouldn't float.
Back to the ant thing, one can lift many times it's own weight, but scale it up to the size of a cow and it couldn't even support itself, same principles apply to wires or cables for that matter.
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Old 01-08-2014, 11:32   #17
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Re: LED wire size

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Isn't that just the opposite? That is smaller wire in proportion to it's size is stronger.
I believe this called the square cube ratio and explains things for example why an ant can fall from any height, but an elephant cannot jump
When you step on an ant...you scape ant bits off your foot.
If you step on an elephant...and it annoys him, he scrapes bits of you off his foot.

In a static theoretical world with an unsheathed wire, you would be correct but in the real world where it's being jerked and vibrated around with other much heavier objects, the small weight savings doesn't help much.

Also, for small wires, the plastic sheath makes up a large percentage of the weight and downsizing the copper conductor doesn't reduce the weight as much as you might think but it does reduce the tensile strength significantly.
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Old 01-08-2014, 11:48   #18
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Re: LED wire size

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Originally Posted by a64pilot View Post
If hung from only it's own weight a large enough wire cannot even support it's own weight, but a very small one can support many times it's own weight.
I'm not an Engineer and don't know how to prove this, but in scaling up, you don't increase the strength of something proportional to it's size, there is a limit as to how big a fiberglass boat can be built for example, eventually the hull would get so thick that it wouldn't float.
Back to the ant thing, one can lift many times it's own weight, but scale it up to the size of a cow and it couldn't even support itself, same principles apply to wires or cables for that matter.
Actually, that's false.

Using scale is more complicated. The problem with scaling an ant up to the size of a cow is if you double the length, you also double the width and the height. The result is the ants weight increases by a factor of 8.

Assuming an ant is 1/4inch and a cow is 100 inches long, you are increasing the length by a factor of 400 but the weight increases by a factor of 64 million.

In the example with replacing a wire, you are only scaling the diameter but not the length. The strength of a wire is a function of it's cross sectional area, so if you double the diameter, the cross sectional area (and strength) increases by a factor of 4. Since the length is the same, the weight also increases proportional to the cross sectional area, ie: a factor of 4.

The end result is for the same run, if a small diameter wire is strong enough to support itself, any larger diameter can support itself.

The fiberglass boat example follows the full 3 dimensional example so it's not really comparable.
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Old 01-08-2014, 12:03   #19
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Re: LED Wire Size

OK, this is for wire rope, but the principle is the same
Wire Rope Chart

If I do the math right, please check me as my strong point is not math, but a .25" wire rope weighs .12 lb per ft. and has a strength of 6,800 lbs. If you hung a length of 56,666 ft of it, it will just barely support it's own weight.

A 1.0 steel cable however weighs 1.85 lbs per ft. and if you hung a length of 25,405 ft of it, then it can barely support it's own weight.
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Old 01-08-2014, 13:32   #20
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Re: LED Wire Size

I've had absolutely no luck training ants to pull wire thru a mast.

I wouldn't personally use anything smaller than marine-grade #16 duplex in the mast because of the potential force on the wire when pulling it through the mast, and from the stresses of being connected/disconnected at the base of the mast.

If you had a nice conduit, and some sort of mast-mounted connector at the mast base, you could theoretically get away with thinner wire. But a well-installed #16 run will outlast the mast (barring damage or corrosion of the connections).
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Old 01-08-2014, 13:42   #21
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Re: LED Wire Size

64--interesting.
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Old 01-08-2014, 14:04   #22
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Re: LED Wire Size

Yes, definitely interesting. But I don't know who to believe (its the internet, after all).

On the other hand, I am reliably informed that no more than 10 angels can stand on the head of a pin.
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Old 01-08-2014, 14:09   #23
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Re: LED Wire Size

Sounds like, if he sticks with 1/4" steel wire, he'll be OK.
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Old 01-08-2014, 14:51   #24
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Re: LED Wire Size

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Originally Posted by a64pilot View Post
OK, this is for wire rope, but the principle is the same
Wire Rope Chart

If I do the math right, please check me as my strong point is not math, but a .25" wire rope weighs .12 lb per ft. and has a strength of 6,800 lbs. If you hung a length of 56,666 ft of it, it will just barely support it's own weight.

A 1.0 steel cable however weighs 1.85 lbs per ft. and if you hung a length of 25,405 ft of it, then it can barely support it's own weight.
1/4" cable: 6800# divided by 0.12 #/ft = 56,667ft
1" cable: 103,400# divided by 1.85#/ft = 55,892ft

In the engineering world, we call that a rounding error.
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Old 01-08-2014, 18:17   #25
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Re: LED Wire Size

This place is hilarious -

http://www.amazon.com/Ancor-121510-E...ds=marine+wire

~200 foot run = 14ga. assuming around 2a max.

Ants in your mast may influence that. Elephants in your mast may make wire sizing irrelevant.
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Old 01-08-2014, 23:53   #26
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Re: LED Wire Size

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I am replacing my tricolor bulbs with LED's can I use a smaller wire? The run to the mast head is about 65 feet from the panel.
Rich
It's a very simple answer.

Size the wire for the run, assuming it's an incandescent.

If you size it for the VA of an LED, then you will likely burn all the wires in the mast.

When you can't find and LED replacement, and then opt for the incandescent.

What about future owners, that don't know the wire is limited to LED x VA.

You will SHIRLEY be cursed as to what the PO did.

Don't be an IDIOT.

It's all good fun to post up a topic such as this, and then let, all the goofballs come out of the closet, talking about various of reasons, to do or not to do.

Do it by design, one time, and forggeta about it.

You would only save a couple of penny's, at a future costs of the "cube law" x "multiplied inverse law".


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